Overview of Multifocal Electroretinogram
The multifocal electroretinogram, or mfERG, is a new kind of eye test that lets doctors quickly check how well different areas of the retina are working all at once. The test uses a pattern of 64 or 103 black and white hexagons that flicker over a certain area of your field of vision.
As your eyes respond to this flickering pattern, the mfERG makes a kind of map that shows how well various parts of the retina are functioning. This is super helpful because it can help doctors identify any areas in the retina where things aren’t working as they should, whether the problems are spread out or concentrated in a certain zone.
By looking at the results from the mfERG, doctors can get useful information that can help them figure out what might be causing problems with your vision. This is particularly useful when it’s still unclear what’s causing the issues even after a standard eye exam.
Anatomy and Physiology of Multifocal Electroretinogram
The structure of the retina, the part of the eye that captures light, has 10 different layers, each made up of various types of cells and the connections between them. This whole system works together to process visual images.
The inner part of the retina consists of nerve fiber layer axons (the long part of a nerve cell that carries messages), ganglion cells (a type of nerve cell), and amacrine cells (another type of nerve cell). These parts help with the signals coming from the eye to the brain. On the other hand, the outer part of the retina includes rod and cone photoreceptors (light-sensitive cells that start the process of visual interpretation).
Cones, which help us perceive colors and detailed images, are found in the highest numbers in the central part of the retina or fovea (the area of the retina responsible for sharp central vision). After the outer part of the retina has begun to interpret the light it received, the inner part of the retina (the ganglion cells) send this electrical information to the brain via the optic nerve (a pathway from the eye to the brain) where it is processed to form the visuals we see.
Why do People Need Multifocal Electroretinogram
The mfERG, or multifocal electroretinography, is a specialized eye test that goes beyond a normal eye exam. This test may be done for several reasons:
* To help tell the difference between various types of eye diseases that impact the retina (the back part of your eye that senses light)
* To confirm that the disease is not affecting the outer part of the retina
* To track how an eye disease is progressing over time
* To determine whether an eye problem is due to actual physical damage (organic) or other causes that don’t involve physical harm to the eye (nonorganic)
When a Person Should Avoid Multifocal Electroretinogram
There are no specific reasons or conditions that would stop someone from having the mfERG test done.
Equipment used for Multifocal Electroretinogram
To conduct the required procedure, the following tools are needed:
* Electrodes: These are small devices that are placed on your skin to pick up electrical signals from your body. They are completely safe and painless.
* Amplification system: This is a special system that increases the strength of the signals picked up by the electrodes. It ensures that these signals are strong enough to be recorded and analyzed.
* Data recording and display system: This system records all the signals received and displays them in a format that can be easily understood. It helps to track the progress and outcome of the procedure.
Who is needed to perform Multifocal Electroretinogram?
Specialized technicians, who are trained properly, carry out a test called mfERG at large medical centers that have a special area called an electrophysiology laboratory. This test is typically used to look at the function of your retina (the layer at the back of your eye that helps you see). After the test, eye doctors who specialize in issues of the retina and nerves (retina specialists and neuro-ophthalmologists) then look at the test results to understand what’s happening in your eyes.
Preparing for Multifocal Electroretinogram
If you’re having a medical procedure where doctors measure your eyes’ responses using special electrodes, here is what you can expect. The doctors will place different kinds of sensors, called electrodes, on or near your eye. The type of electrode can change how clear the signal is and how long it takes to get a good reading.
There are three types of electrodes: recording electrodes, reference electrodes, and ground electrodes. Recording electrodes are placed either on the surface of your eye or near it, depending on the type of sensor used. Reference electrodes are usually placed on your skin near the corner of the eye being tested, but should not be placed on the forehead, earlobe, or behind the ear. Ground electrodes are typically placed on the forehead and are connected to the system doing the recording.
Before the test begins, some preparations will be made. If a special lens contact lens electrode is used, your pupils (the black part in the middle of your eyes) will need to be as wide as possible. If you have a hard time seeing the spot you need to look at during the test, the doctor may advise you to look straight ahead and keep your gaze steady. Using both eyes for the test is usually recommended because it helps keep your eye steady and makes the test faster. However, if your eyes are not aligned, they may suggest using only one eye for the test.
You will be asked to sit in a comfortable position and relax your neck and face muscles to avoid any twitch or movement that could interfere with the test results. There may be a chin or head rest. Keeping your eye on a target is important, but if it’s difficult for you to focus on the target, it may be moved to a better spot. Also, lenses might be used to help get the best results.
You might need at least 15 minutes of rest in normal room lighting if you had a previous test that required bright light. The room light during your test should be dim or normal, without any bright light or reflections directly in your view.
How is Multifocal Electroretinogram performed
The multifocal electroretinogram (mfERG) is a test used by doctors to measure the electrical signals produced by your eye’s light-sensing cells, the rods and cones. During the test, the doctor is looking closely at the signals that the cones produce, giving a significant idea of how well the cells in your eye are working. The signal tracked in an mfERG test has three main components, which the doctors refer to as N1, P1, and N2.
N1 is the first wave traced in the test and it primarily measures how well the cells outside our retina (the outer part of our eye that receives light) are functioning. P1, on the other hand, represents the response from cells inside the retina and gives doctors an idea of how well cells in the eye are converting light into an electrical signal, a process called phototransduction.
During the mfERG test, doctors are looking at two main things from these waves: their ‘amplitude’ and ‘implicit time’. Amplitude here refers to the maximum electrical response produced by cells in the eye when they detect light. The Implicit time is the time taken for this electrical response to reach its maximum. This can help to tell the doctor how fast signals are being conducted in the eye.
Standard guidelines have been created for the mfERG test by the International Society for Clinical Electrophysiology of Vision (ISCEV) to ensure the test results can be compared across different laboratories.
During the test, the doctor uses a visual display consisting of 61 or 103 black and white hexagons to stimulate your eye. Depending on the number of hexagons, the test can last for a minimum of 4 to 8 minutes. The test time is often broken down into shorter periods to offer you rest and to avoid any mistakes caused by movement or interruptions.
To optimise the test results, the doctor must ensure that the visual display is calibrated to produce the desired light and dark levels. The hexagons on the display follow a specific pattern, changing between dark and light states at a calculated rate which helps in acquiring reliable test results.
In regards to the recorded signal, the doctor will try to remove any distortions or noises that might have been induced artificially by blinks or movements. The signals are then analysed and interpreted by comparing them to standard values. Doctors usually go through the wave diagrams closely to spot areas where signals are weak or delayed. They also create 3D images and plots from the recorded data to help identify potentially damaged areas in the eye.
In conclusion, the mfERG test is a comprehensive way for doctors to understand how well the cells in your eye are working and it assists in diagnosing any eye problems accurately.
Possible Complications of Multifocal Electroretinogram
The mfERG is a safe, simple test that doesn’t hurt much. It involves looking at how the eyes react to certain conditions. While doing the test, some patients might feel mild discomfort in their eyes. In rare cases, depending on the type of equipment used, the eye’s cornea may experience minor scratches.
There are a few things that can affect the accuracy of the test:
* Changes to normal testing conditions. This includes adjusting the light, increasing or decreasing the intensity of the flash, changing the test environment, altering the length of time the patient’s eye is allowed to adjust to the light or darkness, and pupil size.
* Issues with electrodes. These are the devices used to measure the electrical activity in your eyes. If they don’t make good contact with your skin or eye, are placed incorrectly, move around a lot, or have electrical problems, it could affect the test results.
* Eye blinking or movement during the test.
* Problems with focus or untreated vision issues.
* An older person may show less electrical response than a younger person.
* Certain eye conditions that cause cloudiness or blurred vision can impact results.
* Fluctuations in response throughout the day.
* Decreased response when under anesthesia.
* Differences in results depending on the type of device used or between different labs.
Here are some common issues that could affect the mfERG test:
* ‘Line frequency interference’: Other electrical signals interfering with your eye’s signals.
* ‘Movement errors’: Moving your eyes too much during the test.
* ‘Eccentric fixation’: Not looking directly at the target during the test.
* ‘Positioning errors and head tilt’: Holding your head in the wrong position.
* ‘Erroneous central peak’: Weak signals coming from your eyes.
* ‘Averaging and smoothing artifacts’: Issues with how the test averages out your results.
* ‘Blindspot’: Areas in your vision where you can’t see anything, which could affect the test results.
What Else Should I Know About Multifocal Electroretinogram?
The mfERG is a modern eye test that can pinpoint specific parts of the retina – the back part of your eye – that may be damaged. This test is invaluable for both diagnosing uncertain eye diseases and tracking their progression. An abnormal result from this test usually signals damage to the fovea, small pit in the retina, or the bipolar cells, and it helps doctors understand the cause of vision loss. However, this type of test may not pick up damage in the inner retina as clearly.
Retinitis Pigmentosa (RP) is a genetic eye disease that causes damage to the retina, the back part of the eye that captures light and sends signals to your brain. The mfERG test is particularly useful for patients with late-stage RP. Patients in the late stages of RP may show an overall reduction in their mfERG response. This test can also detect signs of retinal dysfunction in people who carry the RP gene but don’t show symptoms.
Hydroxychloroquine, an anti-inflammatory drug used to treat skin and joint conditions, and also looked at for treating COVID-19, can cause harmful side effects to the retina, resulting in a bullseye-pattern of damage known as bull’s eye maculopathy. The mfERG test can help identify patients at high risk of this retina toxicity, allowing doctors to stop the medication before irreversible vision loss happens. Generally, if the mfERG test results are normal, the medication can be continued, with the test repeated annually.
Stargardt’s disease is a genetic eye condition caused by a mutation in the ABCA gene. Patients with this condition typically have poor central vision and might show significantly reduced response in their mfERG test results. A normal mfERG result effectively rules out Stargardt’s disease.
Occult macular dystrophy is a rare, inherited eye disease that causes progressive central vision loss. The mfERG test will show a reduced response in patients with this disease.
Branch Retinal Artery Occlusion (BRAO) is damage to the retina caused by blockage in a branch of the central retinal artery. The mfERG test can show a reduced response in the pattern of the affected retinal artery, even if the retina appears normal.
Multiple Evanescent White Dot Syndrome (MEWDS) is a peculiar retinal inflammatory disease that mostly affects healthy young to middle-aged women. With this condition, the mfERG response will be suppressed in the area corresponding to the blind spot. However, these abnormalities generally correct themselves after a few months.
Alzheimer’s and Parkinson’s diseases are both neurodegenerative conditions that can also manifest in the eye. Abnormal protein buildup and degenerative changes have also been reported in the retina. Changes in the mfERG responses could signal retinal dysfunction in early stages of Alzheimer’s Disease and Parkinson’s Disease, presenting an alternative non-invasive method for diagnosing these diseases.