An ERG is a painless, safe, and non-invasive form of electrophysiological testing conducted to assess the function of the retina. The retina is a transparent structure in the back of the eye responsible for converting light into electrical signals. An ERG is similar to an EKG or EEG, but for the retina. There are several types of ERGs including full field (flash), pattern, multifocal, photic-negative response, amongst others. With an ERG, light stimulates the retina and the electrical responses are measured.

Another electrophysiological test is the visual evoked potential (VEP) which is similar to the ERG, but measures the electrical signal of the optic nerve and brain, rather than the retina. After an electrical signal is formed in the retina, this signal travels to the primary visual cortex of the brain via the optic nerve. Therefore, the VEP is a diagnostic test assessing the signaling from the optic nerve to the primary visual cortex of the brain. This form of electrophysiological evaluation is especially useful when vision loss is suspected to be due to an optic nerve or brain condition. Similar to the ERG, this is a non-invasive, safe, and painless procedure with no side effects. 

 

Electrophysiological testing is performed in addition to other diagnostic tests such as perimetry (visual field) and OCT testing. ERG and VEP further assess your eye health through evaluation of your retina and optic nerve function. These tests are especially useful for accurate diagnosis and management of specific eye conditions. Electrophysiological testing is also extremely helpful in early disease states or when the cause of vision loss is unknown.
Electrophysiological testing assesses the function, rather than the structure, of the retinal layers, optic nerve, and visual pathway to the brain. This information is used to determine which part of the visual pathway is responsible for vision loss and to what degree vision may be affected.

Unless otherwise directed by your physician, continue taking all medications. Avoid hair products and make sure your hair is clean and without ponytails or braids. Dress comfortably. Young children can have calming items such as a blanket, toy, or pacifier. Small children will be allowed to sit in the lap of a parent during testing. lease Please bring your current glasses if possible. This is helpful for the technicians. Depending on the initial testing results, the technician may have you wear a trial frame with lenses during the remainder of the exam. 

The number and types of diagnostic tests needed is dependent on your diagnosed or suspected condition(s). Multiple tests may be performed during your appointment or at separate visits. Therefore exam time varies patient to patient. It is generally best to assume an appointment time of at least an hour.

Full field ERGs are performed with patients comfortable lying down or sitting up. The eyes may be dilated and the patient may sit in a dark room for 20 minutes to “dark-adapt”. The eyes may be numbed with drops. Several electrodes (either contact lenses or wires) are gently placed on the eyes and one electrode is placed on the forehead. Although the test is painless, sometimes patients have a sensation similar to an eyelash being in the eye from the electrodes. Testing is typically done one eye at a time. The patient will then look at a target and see flashes of light designed to stimulate the retina. The flashes start very dim and slowly become brighter. The retinal responses received by the electrodes are interpreted and displayed on a computer screen. This part takes 10-15 minutes. The test may be repeated after the patient is “light-adapted” and with the lights on. During this time flickering lights may also be used. This again takes 10-15 minutes. Rod photoreceptors are tested in the dark with dim light while cone photoreceptors are tested in a normally lit room with brighter lights or flickering lights. The results are then analyzed and interpreted by your eye care professional. Patients do not need to do anything to prepare for ERG testing except not wear makeup before the testing and not rub their eyes after the testing.

Similar to full field ERGs, patients are seated comfortably and electrodes are placed on the eyes and forehead. Testing is performed one eye at a time. The patient will look at a target on the screen (usually an ‘X’) and the screen will display a flashing hexagon pattern for 30 seconds. This test is usually repeated 8 times per eye. The total testing time is approximately one hour. Data is displayed using waveform traces or colored graphs. The results are then analyzed and interpreted by your eye care professional. Patients do not need to do anything to prepare for ERG testing except not wear makeup before the testing and not rub their eyes after the testing.

The most important thing is to relax. This helps ensure reliable test results and an efficient exam. Please refrain from applying makeup or hair products. Please do not rub your eyes after the testing. Our supplies are latex-free, hypo-allergenic, and water soluble. Please inform our staff of any allergies you may have. 

Electrophysiological testing is contraindicated in patients with a history of seizures. Electrophysiological testing is safe for pregnant women and persons with a pacemaker, but please consult with your primary care physician prior to testing. 

Please notify us of any recent changes in vision or eye concerns prior to testing. Eye dryness, itchiness, allergies, or irritation may affect results and may need to be treated prior to testing.

 

Although each medical insurance plan is different, many insurances cover electrophysiological tests especially when such testing is warranted to determine appropriate diagnosis, treatment, or management. Our office can help verify coverage by your insurance.