Thursday, April 30, 2009

300 Power System New Arthrex 300 Power System


Arthrex is launching a new small bone powered instrument system. The Arthrex 300 has a unique ergonomic design that delivers the highest precision due to the optimum balance. It is modular, which allows one system for all small bone applications. With a PEEK housing and Lithium Ion battery technology, it is the only battery powered small bone system of this type on the market. The Arthrex 300 also utilizes brushless motor technology which allows for maximum torque throughout the entire speed range as well as providing a higher level of reliability than other devices.

Battery-powered precision for small bone surgery

For more information, call (800) 934-4404.

Stereo Microscope and Mount for the Sherline Lathe



A stereo microscope is shown mounted to a Model 4000 Sherline lathe. The stereo microscope allows very close inspection of the part while it is being cut with variable magnification from 5x to 100x. It can be purchased separately for use on any existing Sherline lathe or it can be ordered along with the purchase of a new lathe. (Click on photo for larger image.)

The purpose of the microscope and mount

There are a number of circumstances that might make extremely close inspection of the cutting of a part on the lathe important. First of all, this mount can be of use to those whose failing eyesight makes it difficult for them to work on parts. It is also useful for those with normal eyesight who work on extremely small parts. In addition, those who are tasked with working on very high value parts where a mistake can be costly will want to have the best possible view of what they are doing to assure a perfect cut the first time and every time. Added to the value of the purchase of this accessory is the fact that the microscope itself comes as a complete unit with its own base in addition to the lathe mount base, so it can be used apart from the lathe for other inspection purposes in the shop or lab.

The high quality Russian-made optics of this scope rival that of much more expensive European-built scopes, and it's sturdy yet precise construction is a perfect compliment to the precision of your Sherline machine. The image through the stereo eyepieces is bright and sharp from edge to edge. In addition, Sherline has enhanced some of the features of the scope by redesigning the universal joint of the light and adding a filter kit to protect the lens from chips and coolant. As is always the case, clear, illustrated instructions for assembly and use are provided in addition to those that come with the scope itself.
The microscope is shown here with the stand and armrests that come with it. When used as a stand-alone inspection scope, the light source can be mounted in the base with a glass slide under the stage and a reflecting mirror for lighting an object from below as shown here or the metal stage can be used and the light relocated to the pivoting mount on the head to light the subject from the top. Two pairs of eyepieces (8x and 14x magnification) are provided along with a bulb and two spares. The third 8x eyepiece contains a measuring scale. An alternate measuring grid lens is provided in the small white case. An instruction book comes with the scope and Sherline provides a supplement with additional setup information along with the lathe base. A vinyl dust cover (not shown) is also included. (Click on photo to view a larger image.)
Description of the Mount

The base of the mount is easily attached to the lathe crosslide table with two T-nuts and screws. No drilling is necessary. The microscope head is slid down the steel post on the mount and adjusted for height using the locking ring and thumbscrew that come with the microscope. It is then focused on the tip of the cutting tool. An eyepiece adjustment is provided to accommodate the distance between your eyes. The power of magnification can be adjusted from about 5x to over 100x, but we recommend you start with the lowest power first in order to maintain a larger field of view. You can increase the power at any time with the turn of a knob if you need an extra-close look.

Because the mount moves with the table, the microscope remains focused on the tool as the cut is made. The light source is attached to the microscope head, so it remains with it when it is transferred to the lathe. It is mounted on a universal type joint that allows it to be focused right on the part and tool tip, enhancing your vision even further. We have also developed a lens filter kit that is included with the lathe to help protect the microscope lens from chips and coolant.

The mount can be purchased separately if you already own the microscope, having purchased it for your mill. (A mount is also available for the mill as P/N 2127.) Normally the microscope and mount will be purchased together. If you are also purchasing a new Sherline lathe at the same time as the microscope and mount, there is a $25.00 discount available on the lathe. Simply add the letter "M" to the model lathe you choose. For example; if you are purchasing a Model 4400 lathe along with a 2125 microscope and lathe mount, you would designate a model 4400M lathe when ordering.

OPD-Station Comprehensive Vision Analysis Software


The NIDEK OPD-Station software makes a variety of corneal, total eye and internal eye analysis possible using advanced, unique and intelligent functions including the Holladay Summary and Corneal Navigator (optional). The OPD-Station provides various maps such as the OPD HO Map, PSF, MTF, MTF Graph and Visual Acuity Chart in addition to OPD-Scan II maps. For wavefront maps such as the PSF and MTF, clinicians can slelect the target (OPD, Cornea, Internal) and also the type (Total, HO, Group) according to their needs.

Features

* Holladay Summary
The "Holladay Summary" shows the patient where the aberrations are located and how they affect the quality of vision using the Wavefront, MTF, PSF and VA-chart simulations.

Simulation
PSF


Simulation
MTF


Simulation
VA-chart

"Holaday Summary" is developed in cooperation with Jack T. Holladay, MD.
o PSF Simulation
Calculates the Point Spread Function (PSF) based on the OPD-Scan measured data and corneal topography data, and displays in simulation the distribution of the point spread. The Strehl Ratio serving as a metric of the visual quality of the eye is also displayed.

o Retinal Image Simulation
Calculates the distortion of incoming light based on the result of PSF analysis, and displays the simulated retinal image of the projected chart. This simulation can be used in explanations to patients for informed consent.

o OPD HO Map
Displays in diopters the high order aberrations and shows the refractive errors which cannot be corrected with glasses.

o Averaging Multiple Exams
The OPD-Station creates an exam data average from multiple exams. Noise components such as tear film and fixation disparity are excluded, providing more stable and reliable data.

* Corneal NavigatorCorneal Navigator*
Utilizing various corneal parameters from topography, the Corneal Navigator automatically determines corneal features and shows by percentage the possibility of having a condition of normal (NRM), astigmatic (AST), keratoconus suspects (KCS), keratoconus (KC), pellucid marginal degeneration (PMD), myopic refractive surgery (MRS), hyperopic refractive surgery (HRS), and penetrating keratoplasty (PKP).
Instant analysis by the Corneal Navigator helps improve the quality of examination / diagnosis.

Auto Ref / Kerato / Tonometer TONOREFTM I


The TRIumph of Excellence

Three essential measurements combined in one UNIQUE instrument:
The world's first
Auto Refractometer
Auto Keratometer
Non-Contact Tonometer
combination unit.


Compact and User Functional
Compact and User FunctionalThe newer compact, more user friendly design allows for enhanced patient flow by providing Auto Refractometer / Auto Keratometer / Non-Contact Tonometer measurement in one setting.

The user can easily select patient measurement modes and allow easy access to patients eyelids.


NEW TECHNICAL ADVANCEMENTS incorporated in TONOREF® II allow:

- Smooth, Easy transition patient measurement modes
- New Design facilitates quick access to eyelid


Features

* Accuracy of the Refraction
Building on NIDEK's tradition of high quality and accuracy, the TONOREF® II adopts the state of the art measurement principle found in the NIDEK ARK-500 and AR-300 series.

Pupil Zone Imaging Method
SLD (Super Luminescent Diode)

o Improved image quality
o Measurement of densely cataractous eyes and pseudophakic eyes
o Sharper Clearer images than LED

Comparison of image on CCD*
LED (Normal eye) LED (Cataract eye) SLD (Normal eye) SLD (Cataract eye)
LED (Normal eye) LED (Cataract eye SLD (Normal eye) SLD (Cataract eye)
*In-house trial data (Model eye)
* Attractive 5.7-inch VGA Tiltable Color LCD
Tilting color DisplayClear image and data display with user-friendly colored graphical icons help operators easily recognize the data.

New Mire Ring for Screening and Detecting
Display Display
* Comfortable Tonometry Measurement
Recent enhancements such as the advanced APC (Auto Puff Control) and noise reduction provide for a more comfortable patient experience.

* Quick and Accurate keratometer Measurement

* Printer with Easy Loading & Auto Detachment
Newly adopted printer provides fast and auto paper loading capabilities. The built-in auto detachment cuts the data-printed paper automatically.

Tuesday, April 21, 2009

Wavefront Aberrometer Code: OPD-Scan II


The unique OPD-Scan II is an advanced vision-assessment system that combines topography, wavefront, autorefraction, keratometry, and pupillometry — allowing accurate and reliable analysis of corneal aberration.

Download Brochure
Features

* Many more data points than other aberrometers — allowing precise mapping of irregular astigmatism
* OPD Map shows point-by-point eye aberration
* Single-step measurement of corneal topography and refractive error data for reduced alignment errors
* Selectable measurement data for improved reliability
* Fully automated alignment of the XYZ axis
* Fast processing speed
* Improved accessibility to the eye
* Wide measurement range (Sphere -20.0D to +22.0D and Cylinder 0.0D to ±12.0D)
* High-resolution display (10.4 TFT-Color-LCD) with touch-screen operation
* Easy data maintenance with a detachable hard drive
* Networkable

Surgical CO2 Laser Code: COL-1040


The cutting-edge UniPulse™ COL-1040 is engineered for precise beam coincidence and optimal results in a wide range of surgical applications. Plus, UniPulse™ technology provides uniform and rapid CO2 laser energy distribution.

Download Brochure
Features

* Applications: general surgery, aesthetic surgery, ENT, gynecologic surgery
* Flat-beam profile provides uniform energy distribution to tissue – no tissue hot spots
* Optimized variable-pulse width allows effective ablation and tightening with minimal thermal diffusion
* Optimized pulse shape for preferred energy distribution to tissue
* Long, articulated arm for maximum flexibility in numerous surgical applications
* 300 Hz high-speed scanner
* 1.0 mm spot size with adjustable overlap, allowing hyper-fine resolution and uniform coverage
* Ergonomic hand piece for maximum control and comfort
* Integrated purge/suction ports maintain clear surgical field for continuous laser application
* Detachable nosepiece — reusable and autoclavable

Ultrasound Code: US-4000


Nidek’s Ultrasound US-4000 ultrasonic unit offers A/B scan, biometry, and pachymetry — all in a compact, lightweight device. The unique Ultrasound allows high-resolution images from 400 lines of sampling over 60°, displayed on the 1024 × 768 XGA touch-screen monitor.

Download Brochure
Features

* Accurate axial-length and corneal-thickness measurements in either automatic or manual modes
* Available in a single configuration or in combination with the A scan, for maximum cost efficiency
* Extremely fast biometry measurement
* Accurate pacymetry measurement
* No PC required
* Tiltable color LCD touch-screen monitor

Green Laser Code: The GYC-1000


The compact and reliable GYC-1000, solid-state laser photocoagulator, offers the highest level of performance and versatility available. The unique GYC-1000 offers multiple delivery options including slit lamps, Binocular Indirect Ophthalmoscope (BIO), and endophotocoagulation.

Download Brochure
Features

* Diode pumped solid-state laser for extended life and efficiency at low-heat emission
* Digitally controlled instant-duty cycle allows fast speed and high power over prolonged periods
* 1.7 W of laser energy
* User-friendly, detachable control panel for greater ease of use and convenience
* Plugs into any standard power outlet
* Easy connectivity to Nidek’s YAG laser system (YC-1800)

Tuesday, April 14, 2009

A Patient's Guide to Heart Surgery Heart Valve Surgery


See also: Heart Valve Surgery and Minimally Invasive Heart Valve Surgery

Heart Valve Disease

Heart valve disease occurs when a valve doesn't work right. A valve may not open all the way. Or, a valve may have problems closing. If this happens, blood doesn't move through the heart's chambers the way it should.

Heart valves and how they function.

Problems with Your Heart Valves

If a valve doesn't open all the way, less blood moves through to the next chamber. If a valve doesn't close tightly, blood may leak backward. These problems may mean that the heart must work harder to pump the same amount of blood. Or, blood may back up in the lungs or body because it's not moving through the heart as it should.

Problems Opening

Stenosis occurs when a valve doesn't open fully. The valve may have become hardened or stiff with calcium deposits or scarring. So, it's hard to push open. Blood has to flow through a smaller opening, so less blood gets through the valve into the next chamber.

Problems Closing

Insufficiency (also called regurgitation) results when the valve doesn't close tightly. The valve's supportive structures may be loose or torn. Or, the valve itself may have stretched or thinned. Blood may then leak back the wrong way through the valve.

Heart Valve Surgery

During heart valve surgery, one or more valves are repaired or replaced. Repair means that the valve is mended to help it work better. Replacement means your diseased valve is removed and a new valve is inserted in its place. Whether a valve will be repaired or replaced can only be decided once surgery has begun. Your surgeon will talk with you about his or her plans for surgery and any other procedures you may need.

Repairing a Valve

During valve repair, a ring may be sewn around the opening of the valve to tighten it. Other parts of the valve may be cut, shortened, separated, or made stronger to help the valve open and close right.

A Patient's Guide to Heart Surgery Heart Valve Surgery



See also: Heart Valve Surgery and Minimally Invasive Heart Valve Surgery
Heart Valve Disease
Heart valve disease occurs when a valve doesn't work right. A valve may not open all the way. Or, a valve may have problems closing. If this happens, blood doesn't move through the heart's chambers the way it should.
Problems with Your Heart Valves

If a valve doesn't open all the way, less blood moves through to the next chamber. If a valve doesn't close tightly, blood may leak backward. These problems may mean that the heart must work harder to pump the same amount of blood. Or, blood may back up in the lungs or body because it's not moving through the heart as it should.

Problems Opening

Stenosis occurs when a valve doesn't open fully. The valve may have become hardened or stiff with calcium deposits or scarring. So, it's hard to push open. Blood has to flow through a smaller opening, so less blood gets through the valve into the next chamber.

Problems Closing

Insufficiency (also called regurgitation) results when the valve doesn't close tightly. The valve's supportive structures may be loose or torn. Or, the valve itself may have stretched or thinned. Blood may then leak back the wrong way through the valve.

Heart Valve Surgery

During heart valve surgery, one or more valves are repaired or replaced. Repair means that the valve is mended to help it work better. Replacement means your diseased valve is removed and a new valve is inserted in its place. Whether a valve will be repaired or replaced can only be decided once surgery has begun. Your surgeon will talk with you about his or her plans for surgery and any other procedures you may need.

Repairing a Valve

During valve repair, a ring may be sewn around the opening of the valve to tighten it. Other parts of the valve may be cut, shortened, separated, or made stronger to help the valve open and close right.
Replacing a Valve

If a valve can't be repaired, it may be replaced with a prosthetic valve. Two kinds of prosthetic heart valves are available:

Mechanical and biological heart valvesMechanical valves are created from man-made materials. Lifetime therapy with an anticoagulant (sometimes called a "blood thinner") is needed when these types of valves are used. This medication prevents blood clots from forming on or around the valve.

Biological (tissue) valves are taken from pig, cow, or human donors. These valves don't last as long as mechanical valves. But when tissue valves are used, long-term use of an anticoagulant often isn't needed.

Your doctor will talk with you about choosing the best valve for you. Factors weighed include your age, your occupation, the size of your valve, how well your heart is working, your heart's rhythm, your ability to take an anticoagulant, and how many new valves you need.

Reaching Your Heart

To get to your heart, one or more incisions must be made in your chest. For minimally invasive valve surgery, these incisions are most often much smaller than those made for traditional valve surgery. One of two types of incisions may be used. Which type your surgeon chooses depends on the location of the valve and the method of surgery used. Your surgeon will talk with you about which incision you will receive.

Stopping Your Heart

During valve surgery, your heart must not beat. To keep your blood flowing, it is passed through a heart-lung machine. This machine gives oxygen to your blood and pumps the blood back through your body. Your surgeon may choose to connect your body to the machine through the vessels in your heart or through vessels in your groin. Once the valve surgery is done, your heart and lungs take over again.

Repairing or Replacing the Valve

To reach the valve, an incision is made in your heart or aorta. If the valve can be mended, the needed repairs are done. If the valve must be replaced, part or all of the damaged valve and its supportive structures may be removed. The right-sized replacement valve is selected, positioned in the valve opening, and sewn firmly into place. The incision in your heart or aorta is closed. Your heart is then started so it beats on its own again.

Related links:

* A Patient's Guide: Valves of the Heart
* Heart Valve Surgery
* Minimally Invasive Heart Valve Surgery
* Aortic Valve Replacement
* Mitral Valve Repair

What Is Heart Surgery?

Heart surgery is done to correct problems with the heart. More than half a million heart surgeries are done each year in the United States for a variety of heart problems.

Heart surgery is used to correct heart problems in children and adults. This article discusses heart surgeries for adults. For more information about heart surgeries for children, see the Diseases and Conditions Index articles on congenital heart defects, holes in the heart, and tetralogy of Fallot.
Overview

The most common type of heart surgery for adults is coronary artery bypass grafting (CABG). During CABG, surgeons use healthy arteries or veins taken from another part of the body to bypass (that is, go around) blocked arteries. CABG relieves chest pain and reduces the risk of heart attack.

Heart surgery also is done to:

* Repair or replace valves that control blood flow through the heart
* Repair abnormal or damaged structures in the heart
* Implant medical devices that regulate heart rhythms or blood flow
* Replace a damaged heart with a healthy heart from a donor (heart transplant)

Traditional heart surgery, often called "open heart surgery," is done by opening the chest wall to operate on the heart. Almost always, the chest is opened by cutting through a patient's breastbone. Once the heart is exposed, the patient is connected to a heart-lung bypass machine. The machine takes over the pumping action of the heart. This allows surgeons to operate on a still heart.

In recent years, new ways of doing heart surgery have been developed. One new way is called off-pump, or beating heart, surgery. It's like traditional open-heart surgery, but it doesn't use a heart-lung bypass machine.

Minimally invasive heart surgery uses smaller incisions (cuts) than traditional open-heart surgery. Some types of minimally invasive heart surgery use a heart-lung bypass machine and others don't.

These new methods may reduce risks and speed up recovery time. Studies are under way to compare these new types of heart surgery to traditional open-heart surgery. The results of these studies will help doctors decide the best procedure to use for each patient.
Outlook

The results of heart surgery in adults are often excellent. For very ill people with severe heart problems, heart surgery can reduce symptoms, improve quality of life, and increase lifespan.

To understand heart surgery, it's helpful to know how a normal heart works. See the Diseases and Conditions Index article on How the Heart Works for more information.

Saturday, April 4, 2009

Products information>OT8C Fiber Otoscope



The Otoscope is used to view the tympanic membrane and external ear canal to diagnose outer and middle ear pathologies. It is the mostly used device in ENT.

Features:
1. Fiber optics transmit light system, the fiber optics extend to the tip of the instrument for more light output, less glare.
2. 2.5 x magnification
3. Disposable Specula: 2.5mm and 4.0mm
4. Insufflation Port: view tympanic membrane using an insufflator bulb.
5. Smart design, convenient for mobile diagnosis.
6. OT8C is available with AA alkaline or Ni-MH batteries. The model of the bulb is T4954, 2.5V, 1.6W.

Technical Specifications:
Illumination Form: Fiber optics transmit light
Illumination of light spot: The brightness of the tip is =1000 LX
Magnification of lens: 2.5 x
Diameter of ear-specula: 2.5mm, 4.0mm
Insufflation Port: Yes
Type of bulb: T4954 (2.5V, 1.6W)
Rated voltage: 2 AA alkaline or 2 Ni-MH batteries
Electrical Safety Standard: GB9706.1 internal power source

Slit Lamp Digital Adapter


( Manufacturer )
Price per Unit (piece): $595.00


Convert your Slit Lamp to DIGITAl with Optimetrics new Digital Adapter System:

Digital Adapter includes:

- Digital Eyepiece Adapter

- Camera Ring Adapter

DIGITAL CAMERA IS OPTIONAL - NOT INCLUDED.

Note: Diameter of eyepieces should be 23,45 mm for adapter to fit correctly.


Will also adapt to:

- Marco IIB
- Marco III
- Marco V
- Topcon SL-3D
- Burton 825
- Woodlyn H/S Style
- Haag-Streit 900 BM

Digital Cameras that fit our system:

* Sony DSC-W5
* Sony DSC-W7
* Canon Powershot A530
* Canon Powershot A540
* Canon Powershot A560

Products information>HL8000 Medical Headlight


HL8000 series are used for examination and surgical operation in multifarious microsurgery.

Features:
1. Light Source: Our LED lamp without the heat of traditional Halogen headlight. With a color temperature of 6000 Kelvin, this light supplies bright, white, shadow-free light allowing the doctor to see tissue characteristics without distortion.
2. Enjoy the flexibility of operating the headlight using the rechargeable Lithium battery, can use without the direct power source. It is one of the most comfortable lightweight headlights and suitable for all kinds of surgery.
3. The headlight could be used when it is charging.
4. Has low-battery indicator light.
5. Adapts to any Binocular Loupes of Zumax
6. Smart design, convenient for mobile diagnosis.

Specifications:
Diameter of the light spot at a distance of 420mm: 20-80mm
Illumination in 200mm working distance:>32000 LX
Fluctuation distance:12.5mm
Direction of Illumination:Vertical ±25°adjustable
Weight:69g
Illumination Source:Extremely bright light, 5W LED, life 20000 hours continuous burn.
Battery:7.2 V Lithium battery
Battery Run-time:>2.5 hours
Input Voltage:110 VAC / 220 VAC
Maximum Power Input:10W
Electrical Safety Standard:IEC60601.1,class II equipment

Ocular Sussman Four Mirror Goniscope


( Manufacturer )
Price per Unit (piece): $310.00

Ocular Susman Four Mirror Handheld Gonioscope

Four 64° mirrors for complete anterior chamber angle viewing with minimal lens rotation. Directly hand held for easy handling and stability. Choice of large or small holding ring. Small diameter contact surface allows static or dynamic gonioscopy without methylcellulose. Advanced tehnology, multi-layer polymer coating protects mirrors and is compatible with most disinfecting methods.
Product Code

Image Mag.

Contact Diam.

Lens Height

Ring Diam.

Static Gonio FOV
OS4M

.94x

9mm

24.5mm

24.3mm

80°

Products information>Dental Microscope


OMS2300 Surgical Microscope (for Dental)


SPECIFICATIONS:

Microscope
Binocular Tube: 45°or 180°inclinable (optional)
Objective Lens:F250mm with integrated fine focus
Eyepieces :10x/12.5x Wide-field eyepieces for spectacle wearers
Dioptric adjustment range +/-7
Magnification Changer:5-steps, manual magnification changer
Magnification factors:0.4/0.6/1.0/1.6/2.5
Magnification:3.4x/5.4x/8.5x/13.5x/21.2x
(with F250mm objective lens and 12.5x eyepiece)
Pupil Distance:48~78mm
Field of View:65.0/42.0/26.0/16.0/10.4mm
(with F250mm objective lens and 12.5x eyepiece)
Fine Focus Range:12mm, manual

Illumination
Light Source:2 Halogen lamps,150W/15V with fiber-optic cable
Field of View:50mm (with F250mm objective lens)
Filter:Green and Orange integrated, switchable
Power supply:100V/120V/127V/220V/230V/240V 50Hz..60Hz

Stands
Types: Floorstand, Wall mount, Ceiling mount, Floor mount
Balancing: Adjustable spring in the swing arm
Max Cantilever:1100mm (excluding 350mm extension arm)
Lift of swing arm:+/-300mm

Prism Set Gulden 22


( Manufacturer )
Price per Unit (piece): $198.00


Prism Set Gulden 22

Sizes - 1/2-1-2-3-4-5-6-7-8-9-10-12-14-16-18-20-25-30-35-40-45-50.

Gulden’s plastic ophthalmic prism bars have been re-engineered to solve the problem of birefringence which can hinder their use in certain clinical applications. Our exclusive manufacturing process greatly reduces optical strain, producing prisms that virtually eliminate clinical birefringent effects.

Prism birefringence can adversely affect your vectographic testing by degrading target contrast ("image washout”), or in extreme cases, by reversing the eye that sees the target (“vectographic reversal”). Birefringence occurs in ordinary prisms because of optical strain which is due to minute molecular misalignments that occur in plastic manufacturing.

Our prisms are calibrated in the frontal plane position (i.e., posterior surface parallel to spectacle plane) which produces superior diopter accuracy. Prisms are available in our standard square shape (37 X 37 mm), or in our internationally popular “universal” shape which has two rounded corners for ease of use at various angles.

Either shape can be ordered as single prisms, in custom sets or in a choice of seven standard sets of square or universal prisms.

Products information>SR24D Rechargeable Streak Retinoscope


The SR24D rechargeable retinoscope is designed exclusively to determination of the refraction of the eye. The streak retinoscope is found by most practitioners to be easy to use,fast,accurate and especially valuable in determining the axis of astigmatism.

Features:
1. It has a separate control fro steak width and streak rotation. Streak width never changes while rotating.
2. Dependable,constant automatic safe charging for Li-ion rechargeable handles.
3. The powerful,bright bulb ensures easy recognition of neutralisation.
4. 100% Dustproof Housing Maintenance-free operation.
5. The lowest position gives a divergent beam.
6. The highest position focuses the streak at a distance of about 25cm in front of the retinoscope.
7. Battery Run: 3.5 hours continuous
8. Battery Life: approximately 1 year
9. Bulb:3V,2W.
10. Electrical safety: complying with IEC601-1.

Prism Bar Gulden B-16


( Manufacturer )
Price per Unit (piece): $90.00


B-16 Prism Bar

Product Id # 11116

Gulden’s plastic ophthalmic prism bars have been re-engineered to solve the problem of birefringence which can hinder their use in certain clinical applications. Our exclusive manufacturing process greatly reduces optical strain, producing prisms that virtually eliminate clinical birefringent effects.
Prism birefringence can adversely affect your vectographic testing by degrading target contrast ("image washout”), or in extreme cases, by reversing the eye that sees the target (“vectographic reversal”). Birefringence occurs in ordinary prisms because of optical strain which is due to minute molecular misalignments that occur in plastic manufacturing.

Our prism bars are made of extremely high quality plastic, which are optically clear with an index of refraction of 1.49 and a light transmission value of 92%.

The prism bars are available in various horizontal or vertical configurations, in diopter or degree ranges and sizes.

Horizontal - Calibrated in Frontal Postion

History of the Microscope


During that historic period known as the Renaissance, after the "dark" Middle Ages, there occurred the inventions of printing, gunpowder and the mariner's compass, followed by the discovery of America. Equally remarkable was the invention of the light microscope: an instrument that enables the human eye, by means of a lens or combinations of lenses, to observe enlarged images of tiny objects. It made visible the fascinating details of worlds within worlds.

Invention of Glass Lenses
Long before, in the hazy unrecorded past, someone picked up a piece of transparent crystal thicker in the middle than at the edges, looked through it, and discovered that it made things look larger. Someone also found that such a crystal would focus the sun's rays and set fire to a piece of parchment or cloth. Magnifiers and "burning glasses" or "magnifying glasses" are mentioned in the writings of Seneca and Pliny the Elder, Roman philosophers during the first century A. D., but apparently they were not used much until the invention of spectacles, toward the end of the 13th century. They were named lenses because they are shaped like the seeds of a lentil.

The earliest simple microscope was merely a tube with a plate for the object at one end and, at the other, a lens which gave a magnification less than ten diameters -- ten times the actual size. These excited general wonder when used to view fleas or tiny creeping things and so were dubbed "flea glasses."

Birth of the Light Microscope
About 1590, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, while experimenting with several lenses in a tube, discovered that nearby objects appeared greatly enlarged. That was the forerunner of the compound microscope and of the telescope. In 1609, Galileo, father of modern physics and astronomy, heard of these early experiments, worked out the principles of lenses, and made a much better instrument with a focusing device.

Anton van Leeuwenhoek (1632-1723)
The father of microscopy, Anton van Leeuwenhoek of Holland, started as an apprentice in a dry goods store where magnifying glasses were used to count the threads in cloth. He taught himself new methods for grinding and polishing tiny lenses of great curvature which gave magnifications up to 270 diameters, the finest known at that time. These led to the building of his microscopes and the biological discoveries for which he is famous. He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries. During a long life he used his lenses to make pioneer studies on an extraordinary variety of things, both living and non living, and reported his findings in over a hundred letters to the Royal Society of England and the French Academy.

Robert Hooke
Robert Hooke, the English father of microscopy, re-confirmed Anton van Leeuwenhoek's discoveries of the existence of tiny living organisms in a drop of water. Hooke made a copy of Leeuwenhoek's light microscope and then improved upon his design.

Charles A. Spencer
Later, few major improvements were made until the middle of the 19th century. Then several European countries began to manufacture fine optical equipment but none finer than the marvelous instruments built by the American, Charles A. Spencer, and the industry he founded. Present day instruments, changed but little, give magnifications up to 1250 diameters with ordinary light and up to 5000 with blue light.

Beyond the Light Microscope
A light microscope, even one with perfect lenses and perfect illumination, simply cannot be used to distinguish objects that are smaller than half the wavelength of light. White light has an average wavelength of 0.55 micrometers, half of which is 0.275 micrometers. (One micrometer is a thousandth of a millimeter, and there are about 25,000 micrometers to an inch. Micrometers are also called microns.) Any two lines that are closer together than 0.275 micrometers will be seen as a single line, and any object with a diameter smaller than 0.275 micrometers will be invisible or, at best, show up as a blur. To see tiny particles under a microscope, scientists must bypass light altogether and use a different sort of "illumination," one with a shorter wavelength.

Continue > The Electron Microscope
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History of Microscopes

TimelineAnton van Leeuwenhoek - Father of MicroscopyRobert Hooke
Electron Microscope

Scanning Tunneling Microscope - STMThe Scanning Electron Microscope James Hillier
Suggested Reading

Eye Glasses and Glass History History of the Telescope
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* Timeline - History of Microscopes
* Binoculars Under $150.00
* Before You Buy a Microscope
* Anton Van Leeuwenhoek - Biography of Anton Van Leeuwenhoek

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Thursday, April 2, 2009

What Is Cardiac Catheterization?

Cardiac catheterization (KATH-e-ter-i-ZA-shun) is a medical procedure used to diagnose and treat certain heart conditions. A long, thin, flexible tube called a catheter is put into a blood vessel in your arm, groin (upper thigh), or neck and threaded to your heart. Through the catheter, doctors can perform diagnostic tests and treatments on your heart.

Sometimes a special dye is put into the catheter to make the insides of your heart and blood vessels show up on x rays. The dye can show whether a material called plaque (plak) has narrowed or blocked any of your heart’s arteries (called coronary arteries).

Plaque is made up of fat, cholesterol, calcium, and other substances found in your blood. The buildup of plaque narrows the inside of the arteries and, in time, may restrict blood flow to your heart. When this happens, it’s called coronary artery disease (CAD).

Blockages in the arteries also can be seen using ultrasound during cardiac catheterization. Ultrasound uses sound waves to create detailed pictures of the heart’s blood vessels.

Doctors may take samples of blood and heart muscle during cardiac catheterization, as well as do minor heart surgery.

Cardiologists (doctors who specialize in treating people who have heart problems) usually perform cardiac catheterization in a hospital. You’re awake during the procedure, and it causes little to no pain, although you may feel some soreness in the blood vessel where your doctor put the catheter. Cardiac catheterization rarely causes serious complications.

What Is Cardiac MRI?

Magnetic resonance imaging (MRI) is a safe, noninvasive test that creates detailed images of your organs and tissues. “Noninvasive” means that no surgery is done and no instruments are inserted into your body.

MRI uses radio waves and magnets to create images of your organs and tissues. Unlike computed tomography (to-MOG-ra-fee) scans (also called CT scans) or conventional x rays, MRI imaging doesn’t use ionizing radiation or carry any risk of causing cancer.

Cardiac MRI uses a computer to create images of your heart as it’s beating, producing both still and moving pictures of your heart and major blood vessels. Doctors use cardiac MRI to get images of the beating heart and to look at the structure and function of the heart. These images can help them decide how best to treat patients with heart problems.

Cardiac MRI is a common test for diagnosing and evaluating a number of diseases and conditions, including:

* Coronary artery disease
* Damage caused by a heart attack
* Heart failure
* Heart valve problems
* Congenital heart defects
* Pericardial disease (a disease that affects the tissues around the heart)
* Cardiac tumors

Cardiac MRI images can help explain results from other tests, such as x ray and CT scans. Cardiac MRI is sometimes used to avoid the need for other tests that use radiation (such as x rays), invasive procedures, and dyes containing iodine (these dyes may be harmful to people who have kidney problems).

Sometimes during cardiac MRI, a special dye is injected into a vein to help highlight the heart or blood vessels on the images. Unlike the case with x rays, the special dyes used for MRI don’t contain iodine, so they don’t present a risk to people who are allergic to iodine or have kidney problems.

What Is Angina?


Angina (an-JI-nuh or AN-juh-nuh) is chest pain or discomfort that occurs when an area of your heart muscle doesn't get enough oxygen-rich blood. Angina may feel like pressure or squeezing in your chest. The pain also may occur in your shoulders, arms, neck, jaw, or back. It can feel like indigestion.

Angina itself isn't a disease. Rather, it's a symptom of an underlying heart problem. Angina is usually a symptom of coronary artery disease (CAD), the most common type of heart disease.

CAD occurs when a fatty material called plaque (plak) builds up on the inner walls of the coronary arteries. These arteries carry oxygen-rich blood to your heart. When plaque builds up in the arteries, the condition is called atherosclerosis (ATH-er-o-skler-O-sis).
Figure A shows a normal artery with normal blood flow. Figure B shows an artery containing plaque buildup.

Plaque causes the coronary arteries to become narrow and stiff. The flow of oxygen-rich blood to the heart muscle is reduced. This causes pain and can lead to a heart attack.
Types of Angina

The three types of angina are stable, unstable, and variant (Prinzmetal's). Knowing how the types are different is important. This is because they have different symptoms and require different treatment.
Stable Angina

Stable angina is the most common type. It occurs when the heart is working harder than usual. Stable angina has a regular pattern. If you know you have stable angina, you can learn to recognize the pattern and predict when the pain will occur.

The pain usually goes away in a few minutes after you rest or take your angina medicine.

Stable angina isn't a heart attack, but it makes a heart attack more likely in the future.
Unstable Angina

Unstable angina doesn't follow a pattern. It can occur with or without physical exertion and isn't relieved by rest or medicine.

Unstable angina is very dangerous and needs emergency treatment. It's a sign that a heart attack may happen soon.
Variant (Prinzmetal's) Angina

Variant angina is rare. It usually occurs while you're at rest. The pain can be severe. It usually happens between midnight and early morning. This type of angina is relieved by medicine.
Overview

It's thought that nearly 7 million people in the United States suffer from angina. About 400,000 patients go to their doctors with new cases of angina every year.

Angina occurs equally in men and women. It can be a sign of heart disease, even when initial tests don't show evidence of CAD.

Not all chest pain or discomfort is angina. A heart attack, lung problems (such as an infection or a blood clot), heartburn, or a panic attack also can cause chest pain or discomfort. All chest pain should be checked by a doctor.

What Is High Blood Pressure?

High blood pressure (HBP) is a serious condition that can lead to coronary heart disease, heart failure, stroke, kidney failure, and other health problems.

"Blood pressure" is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If this pressure rises and stays high over time, it can damage the body in many ways.
Overview

About 1 in 3 adults in the United States has HBP. HBP itself usually has no symptoms. You can have it for years without knowing it. During this time, though, it can damage the heart, blood vessels, kidneys, and other parts of your body.

This is why knowing your blood pressure numbers is important, even when you're feeling fine. If your blood pressure is normal, you can work with your health care team to keep it that way. If your blood pressure is too high, you need treatment to prevent damage to your body's organs.
Blood Pressure Numbers

Blood pressure numbers include systolic (sis-TOL-ik) and diastolic (di-a-STOL-ik) pressures. Systolic blood pressure is the pressure when the heart beats while pumping blood. Diastolic blood pressure is the pressure when the heart is at rest between beats.

You will most often see blood pressure numbers written with the systolic number above or before the diastolic, such as 120/80 mmHg. (The mmHg is millimeters of mercury—the units used to measure blood pressure.)

The table below shows normal numbers for adults. It also shows which numbers put you at greater risk for health problems. Blood pressure tends to goes up and down, even in people who have normal blood pressure. If your numbers stay above normal most of the time, you're at risk.
Categories for Blood Pressure Levels in Adults (in mmHg, or millimeters of mercury)
Category Systolic
(top number) Diastolic
(bottom number)
Normal Less than 120 And Less than 80
Prehypertension 120–139 Or 80–89
High blood pressure
Stage 1 140–159 Or 90–99
Stage 2 160 or higher Or 100 or higher

The ranges in the table apply to most adults (aged 18 and older) who don't have short-term serious illnesses.

All levels above 120/80 mmHg raise your risk, and the risk grows as blood pressure levels rise. "Prehypertension" means you're likely to end up with HBP, unless you take steps to prevent it.

If you're being treated for HBP and have repeat readings in the normal range, your blood pressure is under control. However, you still have the condition. You should see your doctor and stay on treatment to keep you blood pressure under control.

Your systolic and diastolic numbers may not be in the same blood pressure category. In this case, the more severe category is the one you're in. For example, if your systolic number is 160 and your diastolic number is 80, you have stage 2 HBP. If your systolic number is 120 and your diastolic number is 95, you have stage 1 HBP.

If you have diabetes or chronic kidney disease, HBP is defined as 130/80 mmHg or higher. HBP numbers also differ for children and teens. (For more information, see "How Is High Blood Pressure Diagnosed?")
Outlook

Blood pressure tends to rise with age. Following a healthy lifestyle helps some people delay or prevent this rise in blood pressure.

People who have HBP can take steps to control it and reduce their risks for related health problems. Key steps include following a healthy lifestyle, having ongoing medical care, and following the treatment plan that your doctor prescribes.

Neurology Articles

ehavioral Neurology and Dementia

* Alzheimer Disease
* Alzheimer Disease in Individuals With Down Syndrome
* Aphasia
* Apraxia and Related Syndromes
* Confusional States and Acute Memory Disorders
* Dementia With Lewy Bodies
* Dementia in Motor Neuron Disease
* Dementia: Overview of Pharmacotherapy
* Frontal Lobe Syndromes
* Frontotemporal Lobe Dementia
* Hydrocephalus
* Mild Cognitive Impairment
* Pick Disease
* Spatial Neglect
* Uremic Encephalopathy
* Vascular Dementia


Computer Applications in Neurology

* Medical Informatics in Neurology
* Virtual Reality Biofeedback in Chronic Pain and Psychiatry*
* Virtual Reality to Evaluate Motor Response During Seizure Activity*
* Virtual Reality: Overview of its Application to Neurology*
* Visual-Haptic Interfaces: Modification of Motor and Cognitive Performance*


Critical Care Neurology

* Epidural Hematoma
* Neurologic Complications of Organ Transplantation
* Subdural Hematoma


Electroencephalography and Evoked Potentials

* Abnormal Neonatal EEG
* Ambulatory EEG
* Clinical Utility of Evoked Potentials
* EEG Seizure Monitoring
* EEG Triphasic Waves
* EEG in Brain Tumors
* EEG in Common Epilepsy Syndromes
* EEG in Dementia and Encephalopathy
* EEG in Status Epilepticus
* Epileptiform Discharges
* Focal EEG Waveform Abnormalities
* Focal Status Epilepticus
* Generalized EEG Waveform Abnormalities
* Intraoperative Neurophysiological Monitoring
* Motor Evoked Potentials
* Normal EEG Variants
* Normal EEG Waveforms
* Somatosensory Evoked Potentials: Clinical Applications
* Somatosensory Evoked Potentials: General Principles
* Visual Analysis of Neonatal EEG


Electroencephalography Atlas

* EEG Artifacts
* Encephalopathic EEG Patterns
* Epileptiform Normal Variants on EEG
* Focal (Nonepileptic) Abnormalities on EEG
* Generalized Epilepsies on EEG
* Localization-related Epilepsies on EEG
* Normal Awake EEG
* Normal Sleep EEG


Electromyography and Nerve Conduction Studies

* Assessment of Neuromuscular Transmission
* EMG Evaluation of the Motor Unit: The Electrophysiologic Biopsy
* Femoral Mononeuropathy
* Median Neuropathy
* Meralgia Paresthetica
* Motor Unit Recruitment in EMG
* Myokymia
* Peroneal Mononeuropathy
* Radial Mononeuropathy
* Single-Fiber EMG
* Ulnar Neuropathy


Headache and Pain

* Cervical Spondylosis: Diagnosis and Management
* Chronic Paroxysmal Hemicrania
* Cluster Headache
* Discography*
* Intradiscal Electrothermal Therapy*
* Laser Discectomy*
* Migraine Headache
* Migraine Variants
* Muscle Contraction Tension Headache
* Pathophysiology and Treatment of Migraine and Related Headache
* Pathophysiology of Chronic Back Pain
* Percutaneous Vertebroplasty*
* Persistent Idiopathic Facial Pain
* Postherpetic Neuralgia
* Pseudotumor Cerebri
* Raeder Paratrigeminal Syndrome
* Reflex Sympathetic Dystrophy
* Temporomandibular Disorders
* Therapeutic Injections for Pain Management*
* Thoracic Outlet Syndrome
* Trigeminal Neuralgia


Inflammatory and Demyelinating Diseases

* Acute Disseminated Encephalomyelitis
* Ankylosing Spondylitis
* Bell Palsy
* Diffuse Sclerosis
* Marchiafava-Bignami Disease
* Multiple Sclerosis
* Neurosarcoidosis
* Polyarteritis Nodosa
* Systemic Lupus Erythematosus
* Takayasu Arteritis
* Temporal/Giant Cell Arteritis
* Tolosa-Hunt Syndrome
* Wegener Granulomatosis


Introductory Topics

* Cauda Equina and Conus Medullaris Syndromes
* Clinical Safety in Neurology
* Diseases of Tetrapyrrole Metabolism: Refsum Disease and the Hepatic Porphyrias
* Driving and Neurological Disease
* Medicolegal Neurology: Overview
* Medicolegal Neurology: Special Issues
* Neurologic Disease and Pregnancy
* Neurological History and Physical Examination
* Spasticity
* Spinal Cord Trauma and Related Diseases
* Spinal Cord, Topographical and Functional Anatomy


Movement and Neurodegenerative Diseases

* Ataxia with Identified Genetic and Biochemical Defects
* Botulinum Toxin (BOTOX®): Dystonia Treatment
* Catatonia
* Chorea Gravidarum
* Chorea in Adults
* Cortical Basal Ganglionic Degeneration
* Essential Tremor
* Friedreich Ataxia
* Hallervorden-Spatz Disease
* Huntington Disease
* Idiopathic Orthostatic Hypotension and other Autonomic Failure Syndromes
* Movement Disorders in Individuals with Developmental Disabilities
* Multiple System Atrophy
* Neuroacanthocytosis
* Neuroacanthocytosis Syndromes
* Normal Pressure Hydrocephalus
* Olivopontocerebellar Atrophy
* Parkinson Disease
* Parkinson Disease in Young Adults
* Parkinson-Plus Syndromes
* Pelizaeus-Merzbacher Disease
* Primary Torsion Dystonia
* Progressive Supranuclear Palsy
* Striatonigral Degeneration
* Surgical Treatment of Parkinson Disease
* Surgical Treatment of Tremor
* Syringomyelia
* Tardive Dyskinesia
* Torticollis
* Vitamin B-12 Associated Neurological Diseases
* Wilson Disease
* Writer's Cramp


Neuro-imaging

* Carotid Ultrasound*
* Magnetic Resonance Imaging in Acute Stroke
* Neuroimaging in Epilepsy Surgery
* PET Scanning in Autism Spectrum Disorders


Neuro-oncology

* Benign Skull Tumors
* Brain Metastasis
* Brainstem Gliomas
* CNS Melanoma
* Craniopharyngioma
* Ependymoma
* Glioblastoma Multiforme
* Leptomeningeal Carcinomatosis
* Low-Grade Astrocytoma
* Meningioma
* Metastatic Disease to the Spine and Related Structures
* Oligodendroglioma
* Paraneoplastic Autonomic Neuropathy
* Paraneoplastic Cerebellar Degeneration
* Paraneoplastic Encephalomyelitis
* Pituitary Tumors
* Primary CNS Lymphoma
* Primary Malignant Skull Tumors
* Primitive Neuroectodermal Tumors of the Central Nervous System
* Radiation Necrosis


Neuro-ophthalmology

* Anisocoria
* Migraine Headache: Neuro-Ophthalmic Perspective
* Sudden Visual Loss


Neuro-otology

* Benign Positional Vertigo
* Dizziness, Vertigo, and Imbalance
* Endolymphatic Hydrops
* Labyrinthitis and Related Conditions
* Syncope and Related Paroxysmal Spells


Neuro-rehabilitation

* Neuromodulation Surgery for Psychiatric Disorders
* Urological Management in Neurological Disease


Neuro-vascular Diseases

* Acute Stroke Management
* Anterior Circulation Stroke
* Arteriovenous Malformations
* Basilar Artery Thrombosis
* Blood Dyscrasias and Stroke
* CADASIL (Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy)
* Cardioembolic Stroke
* Cavernous Sinus Syndromes
* Cerebral Amyloid Angiopathy
* Cerebral Aneurysms
* Cerebral Venous Thrombosis
* Dissection Syndromes
* Fibromuscular Dysplasia
* Foix-Alajouanine Syndrome
* Genetic and Inflammatory Mechanisms in Stroke
* Lacunar Syndromes
* Mechanical Thrombolysis in Acute Stroke
* Metabolic Disease & Stroke: Fabry Disease
* Metabolic Disease & Stroke: Homocystinuria/Homocysteinemia
* Metabolic Disease & Stroke: Hyperglycemia/Hypoglycemia
* Metabolic Disease & Stroke: MELAS
* Metabolic Disease & Stroke: Methylmalonic Acidemia
* Neuro-ophthalmic Manifestations of Vascular Eye Diseases
* Neuroprotective Agents in Stroke
* Posterior Cerebral Artery Stroke
* Reperfusion Injury in Stroke
* Stroke Anticoagulation and Prophylaxis
* Stroke Team Creation and Primary Stroke Center Certification
* Thrombolytic Therapy in Stroke
* Transient Global Amnesia


Neurological Emergencies

* Cerebellar Hemorrhage
* Head Injury
* Intracranial Hemorrhage
* Spinal Cord Hemorrhage
* Spinal Cord Infarction
* Status Epilepticus
* Subarachnoid Hemorrhage


Neurological Infections

* Aseptic Meningitis
* Brucellosis
* HIV-1 Associated Acute/Chronic Inflammatory Demyelinating Polyneuropathy
* HIV-1 Associated CNS Complications (Overview)
* HIV-1 Associated CNS Conditions: Meningitis
* HIV-1 Associated Cerebrovascular Complications
* HIV-1 Associated Distal Painful Sensorimotor Polyneuropathy
* HIV-1 Associated Multiple Mononeuropathies
* HIV-1 Associated Myopathies
* HIV-1 Associated Neuromuscular Complications (Overview)
* HIV-1 Associated Opportunistic Infections: CNS Cryptococcosis
* HIV-1 Associated Opportunistic Infections: CNS Toxoplasmosis
* HIV-1 Associated Opportunistic Infections: Cytomegalovirus Encephalitis
* HIV-1 Associated Opportunistic Infections: PML
* HIV-1 Associated Opportunistic Neoplasms: CNS Lymphoma
* HIV-1 Associated Progressive Polyradiculopathy
* HIV-1 Associated Vacuolar Myelopathy
* HIV-1 Encephalopathy and AIDS Dementia Complex
* Haemophilus Meningitis
* Herpes Simplex Encephalitis
* Infectious Myositis
* Intracranial Epidural Abscess
* Leprosy
* Lyme Disease
* Meningococcal Meningitis
* Neurocysticercosis
* Neuroimaging in Neurocysticercosis
* Neurological Sequelae of Infectious Endocarditis
* Neurosyphilis
* Prion-Related Diseases
* Ramsay Hunt Syndrome
* Spinal Epidural Abscess
* Staphylococcal Meningitis
* Subdural Empyema
* Tropical Myeloneuropathies
* Tuberculous Meningitis
* Variant Creutzfeldt-Jakob Disease and Bovine Spongiform Encephalopathy
* Varicella Zoster
* Viral Encephalitis
* Viral Meningitis
* Whipple Disease


Neuromuscular Diseases

* Acute Inflammatory Demyelinating Polyradiculoneuropathy
* Amyotrophic Lateral Sclerosis
* Autonomic Neuropathy
* Charcot-Marie-Tooth and Other Hereditary Motor and Sensory Neuropathies
* Chronic Inflammatory Demyelinating Polyradiculoneuropathy
* Dermatomyositis/Polymyositis
* Diabetic Neuropathy
* Dystrophinopathies
* Endocrine Myopathies
* Focal Muscular Atrophies
* Hemifacial Spasm
* Hereditary Neuropathies of the Charcot-Marie-Tooth Disease Type
* Inclusion Body Myositis
* Kennedy Disease
* Lambert-Eaton Myasthenic Syndrome
* Limb-Girdle Muscular Dystrophy
* Metabolic Myopathies
* Metabolic Neuropathy
* Multifocal Motor Neuropathy With Conduction Blocks
* Myasthenia Gravis
* Neuropathy of Friedreich Ataxia
* Neuropathy of Leprosy
* Nutritional Neuropathy
* Periodic Paralyses
* Primary Lateral Sclerosis
* Sarcoidosis and Neuropathy
* Schwartz-Jampel Syndrome
* Stiff Person Syndrome
* Thyroid Disease
* Traumatic Peripheral Nerve Lesions
* Vasculitic Neuropathy


Neurotoxicology

* Alcohol (Ethanol) Related Neuropathy
* Arsenic
* Central Pontine Myelinolysis
* Cocaine
* Hyperammonemia
* Inhalants
* Lead Encephalopathy
* Mercury
* Methanol
* Neurologic Effects of Caffeine
* Organic Solvents
* Organophosphates
* Toxic Neuropathy
* Uremic Neuropathy


Pediatric Neurology

* Anencephaly
* Atlantoaxial Instability in Individuals with Down Syndrome
* Benign Childhood Epilepsy
* Benign Neonatal Convulsions
* Brain Death in Children
* Cerebral Palsy
* Childhood Migraine Variants
* Chorea in Children
* Churg-Strauss Disease
* Congenital Muscular Dystrophy
* Congenital Myopathies
* Craniosynostosis
* Disorders of Carbohydrate Metabolism
* Dopamine-Responsive Dystonia
* Emery-Dreifuss Muscular Dystrophy
* Epileptic and Epileptiform Encephalopathies
* Facioscapulohumeral Dystrophy
* Febrile Seizures
* First Seizure: Pediatric Perspective
* Guillain-Barre Syndrome in Childhood
* Headache: Pediatric Perspective
* Hypoxic-Ischemic Brain Injury in the Newborn
* Incontinentia Pigmenti
* Infantile Spasm (West Syndrome)
* Inherited Metabolic Disorders
* Landau-Kleffner Syndrome
* Lennox-Gastaut Syndrome
* Lesch-Nyhan Syndrome
* Lysosomal Storage Disease
* Medulloblastoma
* Menkes Disease
* Mental Retardation
* Metabolic Disease & Stroke: Propionic Acidemia
* Migraine Headache: Pediatric Perspective
* Moyamoya Disease
* Möbius Syndrome
* Myoclonic Epilepsy Beginning in Infancy or Early Childhood
* Neonatal Injuries in Child Abuse
* Neonatal Meningitis
* Neonatal Seizures
* Neural Tube Defects
* Neurofibromatosis, Type 1
* Neurofibromatosis, Type 2
* Neuronal Ceroid Lipofuscinoses
* Peroxisomal Disorders
* Pseudotumor Cerebri: Pediatric Perspective
* Shuddering Attacks
* Spinal Muscular Atrophy
* Sturge-Weber Syndrome
* Thrombotic Thrombocytopenic Purpura
* Tourette Syndrome and Other Tic Disorders
* Tuberous Sclerosis
* Vein of Galen Malformation
* Xeroderma Pigmentosum


Seizures And Epilepsy

* Absence Seizures
* Antiepileptic Drugs: An Overview
* Complex Partial Seizures
* Epilepsia Partialis Continua
* Epilepsy and the Autonomic Nervous System
* Epilepsy in Adults with Mental Retardation
* Epilepsy in Children with Mental Retardation
* Epilepsy, Juvenile Myoclonic
* First Seizure in Adulthood: Diagnosis and Treatment
* Frontal Lobe Epilepsy
* Identification of Potential Epilepsy Surgery Candidates
* Outcome of Epilepsy Surgery
* Partial Epilepsies
* Posttraumatic Epilepsy
* Preeclampsia and Eclampsia
* Presurgical Evaluation of Medically Intractable Epilepsy
* Psychiatric Disorders Associated With Epilepsy
* Psychogenic Nonepileptic Seizures
* Reflex Epilepsy
* Seizures and Epilepsy: Overview and Classification
* Seizures in the Emergency Department
* Simple Partial Seizures
* Sudden Unexpected Death in Epilepsy
* Temporal Lobe Epilepsy
* Tonic-Clonic Seizures
* Vagus Nerve Stimulation
* Women's Health and Epilepsy


Sleep-Related Diseases

* Insomnia
* Narcolepsy
* Normal Sleep, Sleep Physiology, and Sleep Deprivation: General Principles
* Obstructive Sleep Apnea-Hypopnea Syndrome
* Periodic Limb Movement Disorder
* Polysomnography: Overview and Clinical Application*
* REM Sleep Behavior Disorder
* Restless Legs Syndrome
* Sleep Dysfunction in Women
* Sleep Stage Scoring
* Sleeplessness and Circadian Rhythm Disorder
* Somnambulism (Sleep Walking)

Alzheimer Disease in Individuals With Down Syndrome

Background

Alzheimer disease (AD) is the most common form of dementia. It is a progressive degenerative disease of the brain, strongly associated with advanced age. However, it should not be considered a part of the normal aging process. AD is characterized by a relentless progression of symptoms associated with defined neuropathologic changes.

Individuals with trisomy 21, or Down syndrome (DS), develop a clinical syndrome of dementia that has almost identical clinical and neuropathologic characteristics of AD as described in individuals without DS. The main difference is the early age of onset of AD in individuals with DS. These patients present with clinical symptoms in their late 40s or early 50s.

The neuropathology of AD in persons with DS closely resembles the pathology of AD in individuals without DS and is superimposed on developmental abnormalities such as reduced dendritic arborizations, decreased number of spines, spine atrophy, and abnormalities of spine orientation in pyramidal neurons.
Pathophysiology

The reason AD is more frequent in individuals with DS is not known. All recognized mutations for AD are associated with increased deposition of amyloid beta, a peptide fragment from 39 to 43 amino acids long, which are products of the catabolism of the amyloid precursor protein (APP) molecule. The discovery that the APP gene is on the 21st chromosome led to the hypothesis that the early and universal development of AD pathology is due to a third copy of the APP gene. Nonetheless, many steps in the amyloid cascade hypothesis remain unproven.

Epidemiologic and brain imaging studies of patients with AD without DS have led to observations that patients with limited education or diminished baseline cognitive abilities are at increased risk for AD. These data have led to the cognitive reserve hypothesis, which suggests that patients with better baseline cognitive abilities can tolerate more AD pathology and neuronal loss than patients with worse baseline cognitive abilities. Because most patients with DS are mentally retarded and have limited baseline cognitive ability, the cognitive reserve hypothesis would suggest that patients with DS are at increased risk to develop AD.
Frequency
United States

Several studies document that most if not all individuals with DS develop AD. This is unrelated to the degree of mental retardation; AD is not more prominent in individuals with mental retardation from other causes. Due to better clinical management, most persons with DS now reach the age of 40 years. Thus, the frequency of AD is likely to increase.

The percentage of people with DS and AD varies in some of the epidemiologic studies presented. A review of these studies showed that 10-25% of patients had AD when aged 40-49 years, 20-50% had AD when aged 50-59 years, and 60-75% had AD when older than 60 years.
International

No particular geographic distribution exists. A similar clinical picture has been described in other countries.
Mortality/Morbidity

The disease is responsible for the sharp decline in survival in DS patients older than 45 years.
Race

No documentation exists that race influences prevalence.
Sex

In patients without DS, the influence of sex on the incidence and prevalence of AD remains controversial. Some, but not all, studies suggest that the prevalence is higher in women than men. Few studies have evaluated the influence of sex on AD in patients with DS and the results have been contradictory.
Age

* Age and the presence of trisomy 21 are the most important factors in disease development.
* The neuropathologic findings related to AD have been described in all DS individuals older than 35 years.
* Early clinical signs and symptoms are observed at the end of the fifth decade to the beginning of the sixth decade of life. Mean age at the time of clinical diagnosis is 51 ± 6 years.

Clinical
History

* This progressive neurodegenerative disorder affects multiple components of the central nervous system (CNS). The clinical signs and symptoms are an expression of continuous progressive neuronal dysfunction and death.
* One of the most sensitive and specific symptoms of Alzheimer disease (AD) in people without Down syndrome (DS) is a decline in the patient's ability to perform cognitive tasks related to employment, shopping, or household finance. When individuals with DS are employed or performing complex tasks with certain degree of personal autonomy, noticing early signs of the disease might not be difficult. Because most individuals with DS have mental retardation, a history of decline in high level premorbid cognitive abilities is usually difficult to document.
* On average, approximately 1-2 years elapse between the early signs of the disease and the confirmation of the diagnosis.
* In the author's research, typically the first symptoms, most often identified retrospectively, are observed when the patient is aged 50 years (range 36-62.5 y), and the diagnosis is confirmed at age 52.6 years (range 37-62 y). Death occurs at a mean age of 60.11 years (range 46.7-69.8 y). The author's research has also shown that the duration of the disorder from first symptoms to death is 9.10 years (range 6.9-11.10 y), and duration from diagnosis to death is 8.2 years (range 5-12.4 y).
* The main symptoms are confusion, disorientation, and wandering. In most instances, these early signs are not recognized and commonly are misdiagnosed.
* Longitudinal studies showed a progression of cognitive decline with subtle memory loss as early symptoms, which are associated with deficits in visuospatial organization.
* Behavioral changes
o In the early stage of the disease, behavioral changes are the most common sign. These changes are usually considered an exaggeration of long-standing behavioral traits. For example, refusal to follow certain orders or to do chores at home may be perceived as stubbornness.
o Since the early changes are subtle, only those familiar with the individual recognize these changes. Such changes include change in daily routine, change in sleeping or eating habits, inability to make clothing decisions, getting lost in familiar environments, and inability to remember the names of familiar people.
o One of the potentially early signs of AD in highly functional DS individuals is the inability to perform job duties.
* Visual deficiencies
o Impairment in visual perception as a consequence of central processing dysfunction has been described in the early stage of AD in individuals with DS who have a relatively high level of intelligence.
o Central processing dysfunction is more difficult to delineate in patients with DS who have severe mental retardation.
o These central changes are magnified by peripheral visual disorders (eg, cataracts, myopia, astigmatism), which frequently are present in people with DS.
o The visual deficiencies may be responsible for individuals getting lost in familiar environments, not being able to perform activities that require visuomotor coordination, increased frequency of accidents and falls, and difficulty in learning new tasks.
* Impaired learning ability is usually present in the early stages of the disease but is difficult to demonstrate in people with a moderate (or more severe) degree of mental retardation.
* Other indications of early deterioration include loss of language and other communication skills, impairment of social and adaptive skills, and progressive loss of activities of daily living (ADL) (eg, personal hygiene, dining skills, bathroom skills).
* Middle stage
o ADL markedly deteriorate. The patient may depend totally on others for activities such as dressing, eating, walking, and toilet needs.
o Communication skills are reduced markedly. Speech and language, if present, are not used efficiently.
o Behavioral problems are exaggerated, and psychotic behavior may be displayed. Social activities are reduced to a minimum.
* Advanced stage
o Patients are almost at a vegetative level.
o They totally depend on others and interact minimally with the environment.

Physical

The clinical evolution of physical symptoms is similar to that observed in individuals with AD but without DS.

* Motor disorders
o Motor disorders become obvious in the middle and advanced stage of the disease.
o Motor disorders are associated with a progressive gait disorder and in some patients, a parkinsonian syndrome.
o In very advanced stages, the patient is confined to bed with marked rigidity and little voluntary movement.
* Eating/swallowing disorders
o In the author's research, eating disorders with progressive dysphagia and frequent choking may be observed at the beginning of the disease but are more obvious in the middle stage.
o Aspiration pneumonia is a frequent complication.
o Changes in the diet and type of food may help ameliorate the dysphagia; in some patients, tube feeding may be necessary.
* Epileptic seizures
o In the author's research, epileptic seizures of the tonic-clonic type have been described. These occur approximately 2.4 years (range 7 mo to 6.1 y) after the disease presents.
o Usually generalized tonic-clonic seizures are infrequent; if present, they typically can be controlled with antiepileptic medication.
* Myoclonus occurs more frequently than tonic-clonic seizures. The myoclonus may be stimulus sensitive and can be induced by light or a simple touch. In the advanced stages, myoclonus may be constantly present.
* The following information is from the author's personal experience with institutionalized DS individuals. These data may help those who plan services for individuals with DS and AD.
o Communication/speech disorder: Early indication of the impairment was observed after an average of 1.4 years (range 0-4 y; "0" implies the presence of symptoms at the time of first evaluation), and total loss of function occurred approximately 4.5 years (range 2.5-6.8 y) after confirmation of diagnosis.
o ADL: Early indication of failure was observed at an average of 5 months (range 0-1.8 y), and total loss of function occurred 4.5 years (range 1.5-6.5 y) after confirmation of diagnosis.
o Ambulation: Early signs of deterioration were observed after 1.1 years (range 0-3.7 y), and total loss of ambulation occurred 4.6 years (range 2.5-7.4 y) after confirming the diagnosis.
o Leisure activities: Early indications of deterioration were observed after 10 months (range 0-2.9 y), and total loss of the ability to participate in leisure activitieswas seen after an average of 4.1 years (range 1.5-6.5 y).
* The following is the author's account of disease evolution in an individual who was observed from disease onset. This example demonstrates the complexity of the medical issues involved.
o A male, born in 1930, was admitted to an institution for individuals with mental retardation in 1939. He died in the institution in 1991.
o Diagnosis of DS was confirmed by chromosomal analysis.
o Clinical presentation before the beginning of AD was as follows:
+ No behavioral problems; was pleasant and congenial
+ Followed simple commands and understood simple orders
+ Walked independently and also was independent in ADL
+ Normal diet
+ Performed housework and showered well
+ Good leisure skills and active social program; participated in dances and outdoor trips and sang with the radio
+ Understood that he had to leave the building when a fire alarm sounded
+ Score on Vineland Adaptive Behavior Scale in 1975, when aged 45 years, was 4.9 years; remained the same when he was aged 49 years
o The following is a yearly description of his symptoms as he developed AD:
+ 1981 (age 51 y): First symptoms were disorientation, confusion, and behavior changes. He refused to accept that the program activity in which he was involved was over. He refused to return to his residence. He was found wandering the grounds crying and yelling in a state of confusion.
+ 1982 (age 52 y): He showed increased forgetfulness and had emotional problems and periods of agitation manifested by verbal outbursts and throwing of objects.
+ 1983 (age 53 y): ADL needed consistent prompting. He was still capable of showering and changing clothes daily. Leisure skills were unchanged. He exhibited 3 incidents of major aggression and agitation. His score on the Vineland Adaptive Behavior Scale decreased to 3 years.
+ 1984 (age 54 y): He demonstrated poor participation in social activities due to frequent sleeping; ADL needed increased assistance, although he remained independent. A choking episode was observed.
+ 1985 (age 55 y): Regression steadily continued. Disorientation, confusion, wandering, forgetfulness, and sleeping increased. Behavior deteriorated; he would undress in the dining room and at work. ADL also regressed, and he needed more help; however, he remained independent. He frequently was found wandering outside his residence and unable to find his way. Occasionally, he could not find his bedroom. The score on the Vineland Adaptive Behavior Scale decreased to 2.1 years.
+ 1986 (age 56 y): The patient exhibited photomyoclonic response; he had myoclonic seizures and difficulty walking. ADL regressed further; he still could eat and drink but had to be reminded constantly to do so. He was transferred to a safer and more restrictive environment.
+ 1987 (age 57 y): Generalized tonic-clonic seizures appeared. He became aggressive, and his gait deteriorated markedly, but he was still able to walk. He occasionally needed a wheelchair. He fed himself using adaptive equipment. Toilet training was scheduled, but a few accidents occurred.
+ 1988 (age 58 y): He became lethargic. Inappropriate behavior became frequent. He no longer was able to walk independently or feed himself. He frequently lost sphincter control. He could not tolerate bus rides into the community. He still enjoyed music and expressed pleasure by smiling and laughing.
+ 1989 (age 59 y): He developed aspiration pneumonia. He was totally dependent for ADL. He required a wheelchair, and his social interaction became very poor. He developed urinary incontinence.
+ 1990 (age 60 y): He suffered from frequent bouts of pneumonia. He no longer was able to swallow and was fed through a nasogastric tube; a feeding tube (percutaneous endoscopic gastronomy) was placed. Incontinence required the use of diapers. He had minimal interaction with his surroundings and slept most of the time. Occasionally, he conveyed pleasure and displeasure by laughing or crying.
+ 1991 (age 61 y): He showed minimal response to environmental stimulation and slept most of the time.

Causes

* For patients with or without DS, age is the most important risk factor for AD.
* See Alzheimer Disease for a discussion of risk factors for sporadic and autosomal dominant AD.
* A few case studies suggest that persons with DS and atypical karyotypes (partial trisomies, mosaicism, translocations) may have a lower risk of AD than patients with full trisomy.
* Other chromosome 21 genes, such as the gene coding for superoxide dismutase-1 (SOD-1), may be involved. The increased activity of this enzyme may result in increased production of hydroxy radicals, which may accelerate the progression of the disease. SOD-1 activity has been reported to be increased in people with DS.
* In patients without DS, the APOE epsilon 4 allele is associated with increased risk of AD, and the epsilon e2 allele may be protective. Among patients with DS, several studies have demonstrated that the epsilon e2 allele may be protective. Data that the e4 allele increases risk in patients with DS is less compelling than it is for patients without DS.
* Small head circumference, a small brain, low level of intelligence, and a history of head trauma have also been related to a higher incidence of AD. However, none of these factors have been evaluated in individuals with DS.
* Factors that may decrease risk (eg, Mediterranean diet, active life style) or increase risk (eg, cardiac and cerebrovascular disease, small head circumference) of AD in patients without DS have not been evaluated in patients with DS.

Epileptiform Discharges

Author: Edward B Bromfield, MD, Associate Professor of Neurology, Faculty Member, Division of Sleep Medicine, Harvard Medical School; Chief, Division of EEG, Epilepsy and Sleep Neurology, Consulting Neurologist, Brigham and Women's Hospital
Contributor Information and Disclosures

Updated: Sep 27, 2006

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Introduction

Background

Although no longer used for identification and localization of gross structural brain lesions, electroencephalography (EEG) remains the primary diagnostic test of brain function. Unlike relatively new functional imaging procedures, such as functional MRI (fMRI), single-photon emission computed tomography (SPECT), and positron emission tomography (PET), EEG provides a continuous measure of cortical function with excellent time resolution and is relatively inexpensive. EEG is especially valuable in investigation of patients with known or suspected seizures.

Seizures are infrequent events in the majority of patients, making recording of ictal EEG both time-consuming and expensive. The mainstay of diagnosis, therefore, remains detection of interictal (ie, between seizures, from the Latin icere, to strike) epileptiform discharges. Continuous video-EEG monitoring, developed over the last 20 years to facilitate recording of ictal events, also greatly increases the time available to detect interictal epileptiform discharges (IEDs). In the diagnosis of epilepsy and localization of seizure onset, these can be as useful as ictal recordings.

History

Interictal and ictal epileptiform EEG patterns were first identified in the 1930s, leading to distinction between partial and generalized seizures. The basic concepts developed by such pioneers as Fred and Erna Gibbs, William Lennox, and Herbert Jasper underlie our current understanding of the clinical neurophysiology of epilepsy; subsequent work has led mainly to improvements in detection and interpretation of findings they first noted decades ago.

Definition and classification of interictal discharges

The International Federation of Societies for Electroencephalography and Clinical Neurophysiology (IFSECN) describes interictal discharges as a subcategory of "epileptiform pattern," in turn defined as "distinctive waves or complexes, distinguished from background activity, and resembling those recorded in a proportion of human subjects suffering from epileptic disorders…." This somewhat circular definition makes clear that criteria must be verified empirically.

Interictal discharges may be divided morphologically into sharp waves, spikes, spike-wave complexes (also called spike-and-slow-wave complexes), and polyspike-wave complexes (also called multiple-spike-and-slow-wave-complexes). In practical terms, the morphological distinctions are less important than the certainty with which these entities can be distinguished from physiologic or nonspecific sharp transients. IEDs may occur in isolation or in brief bursts; bursts longer than a few seconds are likely to represent electrographic seizures rather than interictal discharges.

The following definitions are in use (IFSECN, 1974):

* Sharp wave - Transient, clearly distinguishable from background activity, with pointed peak at conventional paper speeds and a duration of 70-200 milliseconds (ms)
* Spike - Same as sharp wave, but with duration of 20 to less than 70 ms
* Spike-and-slow-wave complex - Pattern consisting of a spike followed by a slow wave (classically the slow wave being of higher amplitude than the spike)
* Multiple spike-and-slow-wave complex - Same as spike-and-slow-wave complex, but with 2 or more spikes associated with one or more slow waves

Pathophysiology

The underlying cellular pathophysiology of focal spikes is believed to be the "paroxysmal depolarization shift" (PDS). Several decades of studies using cortical application of penicillin or other excitatory agents have revealed a stereotyped neuronal correlate of the interictal spike as recorded at the cortical surface. Sustained neuronal depolarization mediated by an influx of calcium ions underlies a train of action potentials associated with sodium influx. Repolarization and usually hyperpolarization, mediated mainly by potassium, follow this sustained depolarization. The corresponding extracellular field, forming the basis of the surface EEG, shows a negative peak during calcium and sodium influx, falls back to and then below baseline during hyperpolarization, and finally returns gradually to baseline.

The PDS is a model based on intracellular and extracellular single-cell recording. In vivo, however, neuronal networks in hippocampus and neocortex are critical to production of both interictal and ictal discharges. A neuronal network involving thalamus as well as cortex is responsible for producing the generalized spike-wave complex that is the hallmark of idiopathic generalized epilepsies; this network is similar to that thought to be responsible for generating sleep spindles. A complex interaction of excitatory and inhibitory firing of thalamic reticular, thalamic relay, and neocortical pyramidal neurons generates the rhythmic burst firing underlying spike-wave complexes. The slow wave of the complex is thought to represent an inhibitory event, consistent with the major clinical manifestation of arrest of activity in generalized absence seizures (see Absence Seizures).

Simultaneous scalp and intracranial EEG recording has revealed that standard electrodes record only a relatively small proportion of spikes detectable at the cortical surface. Involvement of a relatively large cortical area, 6-10 cm2, is required for spikes to be recorded at the scalp.
Distinction From Normal or Nonspecific Sharp Transients

Perhaps the greatest challenge that faces the novice electroencephalographer is to distinguish true epileptiform discharges from normal or nonspecific sharply contoured waveforms. The latter can be divided into physiologic transients, stereotyped normal EEG variants (see Normal EEG Variants), or nonspecific waveforms.

Sharply contoured physiologic phenomena

These are recognized readily because of their state dependence, characteristic localization, and reactivity.

Vertex waves and K-complexes

Vertex waves appear in late stage 1 sleep, persist into deeper stages, and are maximal over the vertex, with variable but usually symmetric spread to parasagittal head regions. K-complexes correspond to partial arousals and first appear in stage 2. All the sleep-related vertex phenomena can be sharply contoured, especially in children.

Positive occipital sharp transients of sleep

Positive occipital sharp transients of sleep (POSTS) appear in drowsiness and light sleep. They can occur in isolation or in 4- to 6-Hz trains. Analysis of polarity at the occipital leads shows a surface positivity that is relatively uncharacteristic of epileptiform discharges.

Mu rhythm

This central sensorimotor phenomenon is typically a rhythmic discharge at 8-11 Hz, having a comblike, sharp morphology, which transiently suppresses with active or passive movement, or with thinking about movement, of the contralateral limb. Fragments of the mu rhythm can appear at times; the characteristic morphology and frontocentral, central, or centroparietal topography aid in identification.
Normal variants and patterns of uncertain significance

Wicket spikes

These waves have an arciform appearance with a negative sharp component similar to that of mu, and usually occur in brief bursts at frequencies of 6-11 Hz. They are most common in older adults during drowsiness and light sleep. When isolated, especially in combination with nonspecific temporal slowing common in elderly patients, they can be confused easily with epileptiform discharges. However, they have symmetric upslope and downslope, do not cross the baseline, and do not significantly interrupt the background (see Media file 1, lower tracing).

14- and 6-Hz positive spikes

These are characteristically maximal in posterior temporal areas and have a typical combination of 5- to 7-Hz and 13- to 17-Hz frequencies. The spiky portion of the waveform has a surface positive polarity. This pattern is common in adolescents and young adults and appears in drowsiness and light sleep.

Rhythmic temporal theta bursts (psychomotor variant)

These notched or sharply contoured 5- to 6.5-Hz waves occur in bursts or runs, appear in early drowsiness, and usually disappear in stage 2 sleep. They often shift sides during a given recording. Since they may last more than 10 seconds, they can be confused with ictal as well as interictal discharges.

Subclinical rhythmic epileptiform discharge of adults

Subclinical rhythmic epileptiform discharge of adults (SREDA) is an unusual pattern that is maximal over parietal regions and mimics an ictal discharge; it may be preceded by what appear to be isolated sharp waves in the same region. SREDA never has a clinical correlation and typically is recorded in older patients without seizures.

"Phantom" spike-waves

The classic form has very small, often surface-positive, spike components linked to 5.5- to 6-Hz theta waves, and a posterior or ill-defined field. A transitional form that is more anterior and associated with a larger spike may constitute atypical spike-wave complexes and occur in association with generalized epilepsies. The more typical, benign posterior variant may overlap with 14- and 6-Hz positive spikes.

Benign epileptiform transients of sleep

The benign nature of these steeply contoured, very sharp temporal discharges is still debated; similar discharges can be associated with epilepsy when they are frequent, consistently unilateral, or associated with focal slowing. They also are called "small sharp spikes."
Nonspecific sharp transients

The EEG consists of a spectrum of frequencies whose relative power is varying constantly. Sharply contoured waves can occur as a result of random superimposition of different frequency waves. As noted above in relation to wickets, nonspecific sharp transients lack the following characteristics of IEDs:

* Interruption of background true epileptiform discharges (see Media file 1): rhythms
*
* Asymmetric upstroke and downstroke, with downstroke usually being less steep and descending below the baseline
*
* Aftercoming slow wave

In general, interpretation of any single waveform should be conservative; if truly pathological, it generally will recur during the recording, especially if sleep is included.
Localization and Clinical Significance of IEDs

The fundamental distinction between partial and generalized seizures is reflected in the dichotomy of focal and generalized ictal and interictal discharges. Since recording seizures is rare in routine clinical practice, interictal discharges, along with the history, form the basis of distinguishing seizure types and their corresponding epileptic syndromes. Specifically, the distinction between complex partial and absence seizures, or between primarily and secondarily generalized tonic-clonic seizures, often depends on determining whether interictal discharges are focal or generalized.

Focal discharges

Focal discharges manifest as sharp waves or spikes (see Media file 2); aftercoming slow waves help to distinguish these from nonspecific transients, but are not as prominent as in spike-wave complexes. Localization is usually straightforward from recordings made using the 10-20 system, but supplementary electrodes are often useful. Computerized mapping techniques continue to advance and may be helpful in specific cases.

Temporal

The temporal area is the most common location of partial seizure generation and of interictal discharges. An electrical field's maximum at F7/F8 usually indicates anterior temporal location, especially if T3/T4 (T7/T8 in the new terminology) also is involved significantly, while maxima at T3/T4 indicate mid-temporal, and T5/T6 (P7/P8), posterior temporal, locations. Supplementary T1/T2 (ie, true anterior temporal) or zygomatic surface electrodes, or sphenoidal leads, can be more sensitive in recording anterior or mesial temporal discharges. Nasopharyngeal electrodes are uncomfortable and prone to artifact, and are not recommended currently.

Frontal

These may show maxima at frontopolar (Fp1/Fp2), dorsolateral frontal (F3/F4, possibly with spread to C3/C4), orbitofrontal (F7/F8, usually with frontopolar spread), or mesial (Fz-Cz) locations. Seizures arising at these different locations have different clinical characteristics (see Frontal Lobe Epilepsy). So-called secondary bilateral synchrony may occur, in which case distinction from generalized discharges is difficult, although a persistent asymmetry of amplitude and side of onset, as well as ipsilateral focal slowing, can be helpful in identifying the epileptogenic frontal lobe.

Parietal

P3/P4, possibly with central spread, is a less common location for seizure generation or interictal spikes.

Occipital

Discharges maximal at O1/O2 are tied less strongly to clinical epilepsy than discharges at other locations, especially in children. The special circumstance of "needle-like occipital spikes of the blind," occurring with congenital blindness in early childhood, has no relation to seizures.

Lateralized

Sometimes discharges are widespread over one hemisphere.

Multifocal

Typically, this term refers to independent discharges occurring in each hemisphere, arising from at least 3 distinct locations that are separated by more than one interelectrode distance.
Generalized discharges

Generalized discharges usually take the form of spike-wave or polyspike-wave complexes, and involve both hemispheres more or less symmetrically, most often with a midfrontal maximum at Fz, F3, and F4 (see Media file 3). Exceptions exist, with frontopolar or occasionally posterior maxima. Although these discharges are usually bilaterally synchronous and symmetric, amplitude maxima may shift from side to side within the same record or in serial recordings in the same patient.

Frequency of the spike-wave bursts can be approximately 3 Hz (classical or typical), 4-6 Hz (atypical), or less than 2.5 Hz (slow). Both typical and atypical discharges occur in idiopathic/genetic syndromes, and slow spike-wave complexes usually are seen in symptomatic or cryptogenic epilepsies, in which epilepsy results from a widespread insult to the central nervous system. Those interpreting the results should recognize that, during sleep, even classic or atypical spike-wave complexes usually become slower, are less than 2 Hz, occur in isolation rather than in bursts, and can include polyspikes.
Distinction From Ictal Discharges

An unsettled controversy in EEG concerns whether IEDs are fundamentally distinct from ictal discharges or in fact represent just very brief seizures. The answer to this question may vary with seizure and syndrome type.

Focal ictal vs interictal patterns

Although experimental evidence exists indicating that focal neurological dysfunction corresponds to isolated interictal discharges, EEG partial seizure patterns rarely resemble repetitive spikes or sharp waves. Partial seizures typically show a complex evolution, sometimes beginning with repetitive activity in the alpha or beta band, followed by slowing to the theta and then delta range as the discharge increases in amplitude and spreads topographically. Furthermore, seizures typically are followed, but not preceded, by an increase in IED frequency that lasts for hours to days.

On the other hand, recent fMRI studies have shown blood volume (and by implication, blood flow and metabolism) increases, analogous to those observed during seizures, to be associated with isolated IEDs. Similar effects mimicking ictal discharges can be observed with respect to cardiac rhythm changes and increases in prolactin secretion.

Periodic discharges

Repetitive IEDs generally indicate a higher risk of seizures than sporadic discharges. When continuous or nearly so, that is, without intervening background activity, such patterns actually constitute electrographic seizures. When a more distinct interval is noted between discharges (see Media file 4), the pattern is termed periodic (see Focal EEG Waveform Abnormalities) and may constitute a transitional phase between interictal and ictal events. This transitional nature may be confirmed by clear evolution into electrographic seizures, on the one hand, or gradual resolution, usually over several days, on the other.

In cases in which associated epilepsia partialis continua is noted (see Epilepsia Partialis Continua) or with clinical deficits that resolve, along with the periodic EEG pattern, shortly after administration of antiepileptic drugs, an ictal state can be assumed.

Generalized ictal vs interictal patterns

Absence: With respect to generalized spike-wave complexes, morphologies of ictal and interictal discharges are essentially identical, and the only difference is one of duration. Studies show that for clinical absences to be detectable, the spike-wave burst must last at least 3-5 seconds. In experimental situations, however, a delay in reaction time can be observed in association with even one spike-wave complex. Clearly, then, the ictal-interictal distinction is somewhat arbitrary in this instance.

Myoclonic: Myoclonic seizures are extremely brief, lasting substantially less than 1 second, and typically correlate with isolated polyspike-wave complexes. This highlights the similarity between ictal and interictal discharges in generalized epilepsies.

Transient cognitive impairment associated with interictal discharges

As already mentioned, both generalized and focal discharges in isolation can be demonstrated to impair sensitive cognitive tasks. Left-sided discharges may affect verbal, right-sided discharges visuospatial, and posterior discharges visual function. This transitory cognitive impairment may be related more to the aftercoming slow wave, presumably an inhibitory event, than to the discharge itself. Recent evidence suggests that medications that suppress interictal discharges may improve behavior in children with mild epilepsy. Valproate, lamotrigine, and levetiracetam probably suppress spikes more than carbamazepine or phenytoin; this is particularly true for generalized spike-wave discharges, which can be aggravated by carbamazepine and perhaps phenytoin.
Clinical Correlations

Frequency in people without seizures

By adhering to rigorously conservative criteria for interictal discharges, the specificity of EEG in the diagnosis of epilepsy in conjunction with the clinical history can be maintained at approximately 90%, comparing favorably to most other tests in clinical medicine. The interpretation of rarely detected IEDs in the EEGs of people without a clinical history of seizures is open to question in individual cases.

As summarized by Niedermeyer (1999), several large studies in the 1940s, especially of presumably healthy military populations, found discharges in 0.3-9%. Generalized spike-wave complexes, likely the most reliably detected abnormality, were found in 0-2.7% of patients in several studies in the following 2 decades; this finding was most frequent among younger patients, an unknown percentage of whom had a family history of epilepsy. Focal discharges were found in 0-6.4%.

Among more than 3000 children aged 6-13 years, Cavazutti et al found discharges in 3.5%, generalized in about one third.1 Over varying follow-up periods, discharges disappeared in most, and 6% developed clinical seizures, many of whom had positive family histories.

In general, then, detection of definite epileptiform discharges, especially in patients who have had one or more suggestive clinical episodes, has a very high positive predictive value for epilepsy. IEDs also can appear in patients without epilepsy who are taking drugs that lower the seizure threshold, such as clozapine; these are not truly false positives, however, since these patients are at increased risk of having a seizure. A similar argument could be applied to family members of patients with genetic epilepsies.

Frequency in people with seizures

Perhaps an even more important clinical problem relates to the sensitivity and the negative predictive value of the test: how strongly does a normal or nonepileptiform EEG argue against the presence of epilepsy?

The percentage of patients with epilepsy who have IEDs on a routine or prolonged EEG varies in relation to whether sleep was recorded, timing of last seizure, age of patients studied, and type of epilepsy (as well as exclusion of patients with nonepileptic seizures). The sensitivity of a single EEG has been estimated to be in the range of 50%, though estimates have ranged from as low as 10% to as high as 77%. After one or more repeat records, at least some of which include sleep, sensitivity rises to the 80-90% range. Even after several days of continuous recording, a small minority of patients with intractable epilepsy, perhaps 2-3%, do not have IEDs detectable on surface recording. This percentage may be higher among patients with well-controlled epilepsy, who typically do not undergo this type of investigation, and in certain types of partial-onset epilepsies of extratemporal neocortical origin.

In general, IEDs are most likely to appear in the recordings of children, within hours or days of a seizure, and in association with idiopathic or symptomatic generalized epilepsies.

Activation techniques and prolonged recording

Most study results agree that sleep recordings increase the sensitivity of EEG, and some suggest that sleep deprivation can increase the yield beyond its effect on promoting sleep. The other commonly used activation procedures, hyperventilation (HV) and intermittent photic stimulation (IPS), occasionally elicit IEDs that do not appear at other times. Both HV and IPS are more effective in inducing generalized epileptiform IEDs than focal IEDs.

Since medications typically have only minor effects on IEDs, delaying or missing medications is not recommended as an activation technique, since it exposes patients to seizure risk without commensurate diagnostic benefit.

Increasing the time of recording clearly makes detection of IEDs more likely, the ultimate extension of this concept being long-term EEG monitoring (with or without video) for several days (see Ambulatory Electroencephalography and EEG Seizure Monitoring). Computerized spike detection programs allow adequate data compression to make this feasible. These algorithms rely on mathematical representations of IED morphology, including sharpness of the peak and interruption of background rhythms. They typically are designed to overdetect possible spikes, since manual screening of detected waveforms can be performed in a very short amount of time relative to what would be needed to review the entire tracing.

Use in medical treatment decisions

As already discussed, detection of IEDs after a transient neurological event greatly increases the likelihood that a seizure was responsible; in most cases, IEDs can be classified as generalized or focal, providing valuable information with respect to syndrome classification and treatment. In the case of a single unprovoked seizure, the risk of recurrence is approximately 20-80% depending on whether the cause is cryptogenic or symptomatic. This risk is increased by a history of previous neurological insult, especially if accompanied by an acute symptomatic seizure and by detection of IEDs. In some studies, particularly those of children, focal IEDs suggest an increased recurrence risk as well, and would tend to favor treatment.

EEG also can contribute to answering the reverse question, ie, whether medications should be stopped after a 2-year or longer period of seizure freedom after the diagnosis of epilepsy is established. For patients with idiopathic generalized epilepsy, EEGs tend to "normalize" when complete seizure control is attained, and lack of IEDs suggests a decreased risk of relapse when medications are withdrawn. However, the type of idiopathic epilepsy syndrome is most important in predicting the chance for remission (eg, good for childhood absence and poor for juvenile myoclonic epilepsy). For patients with partial epilepsy, or in whom IEDs were not seen before treatment, the value of a negative study is less clear.

Although the utility of following EEG results in patients with epilepsy has not been established, some evidence suggests that discharge frequency does reflect seizure frequency and epilepsy duration.

Use in epilepsy surgery

In patients considered for surgical treatment of intractable epilepsy, a consistently well-localized IED provides extremely valuable localizing information, especially if neuroimaging shows a potential epileptogenic lesion, including mesial temporal sclerosis. Occasionally, interictal data may be more reliable than ictal recording(s) for localizing the epileptogenic region. IEDs recorded during waking and rapid eye movement (REM) sleep often are localized more strongly than those recorded during non-REM sleep.

When patients require invasive recording using depth or subdural electrodes, ictal onsets are of more value, since IEDs often are seen at multiple locations, including some that are remote from the site of seizure onset. Intracranial recording performed intraoperatively, termed electrocorticography (ECoG), sometimes is used to tailor lesionectomies or temporal lobectomies, although its value is not established. Consensus is growing that sporadic spikes are not indications for resection of the underlying cortex, whereas repetitive spikes are (see Media file 5).

After surgery, detection of IEDs on routine follow-up studies can suggest an increased risk of relapse, and may influence decisions concerning whether and when to withdraw medications.
Conclusions

IEDs are of fundamental importance in understanding the physiology of epilepsy, and in its diagnosis, classification, and treatment.