What Is an Electroretinogram?

An electroretinogram is designed to measure how well the retina (the light-sensing tissue at the back of the eye) is functioning. It detects the electrical response of different cells to stimulation.

This test will detect whether there are retinal problems in either dark or light conditions. If there is a problem, it will help determine where there are abnormalities in the retina.

This article will focus on the purpose of undergoing an electroretinogram, how to prepare, what to expect during the test and afterward, and how to interpret your results.

A medical procedure referral with a barcode for electroretinography

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Purpose of Electroretinogram

Your healthcare provider may order an electroretinogram to determine if your retina has been damaged and, if so, how to best go about treating this. Damage can result from an inherited condition such as retinitis pigmentosa (causes degeneration of retinal light-sensing cells) or from medications or other causes.

The healthcare provider may recommend this to determine if your retina has been damaged and, if so, how to best go about treating this.

This test can check to see how both the rod cells of the retina (responsible for dark vision) and the cone cells (responsible for light vision) are functioning. The test is done in two phases—one in the dark and the other in the light. It can reveal if there is a problem with either of these types of cells.

Traditional full-field electroretinograms can detect widespread retinal lesions (as with drug toxicities or rod and cone dystrophies) but are not good at detecting smaller retinal lesions.

Newer multifocal approaches sample the electrical activity from hundreds of areas of the retina in minutes. This allows healthcare providers to rapidly map retinal blind spots and other areas of dysfunction, such as in the macula, in the center of the retina.

While electroretinography is the only test that examines the electrical activity of just the retina, there are a couple of other tests that look at electrical signals in the area. These include:

  • Electrooculography (EOG) examines electrical currents in the whole eye. This can be used to identify problems in the retina and elsewhere in the eye.
  • Visually evoked response (VER) measures how well the brain is responding to things that we see.

Risks and Contraindications

An electroretinogram is a safe test. While in most cases there will be no issues, there is the potential for an electrode to scratch the eye's surface temporarily, causing a corneal abrasion. But that's the only real risk here.

Before the Test

If your healthcare provider has recommended an electroretinogram for you or your child, keep in mind that anesthesia may or may not be given. For the most part, this is not necessary since there should be no discomfort.

However, it's important to stay calm, which may be an issue for a young child under the age of 4 or 5. For those in this age range, medication may be given before the test to help the child relax. In most cases, this will not be necessary.


All in all, you should be in and out pretty quickly. The test typically is performed in about 60–90 minutes. Keep in mind that for about 45 minutes you will likely be in a darkened room, viewing different flashes of light.


This is a test that is performed on an outpatient basis and can be done right at your healthcare provider's office.

What to Wear

You can wear whatever type of clothing you are comfortable in. You may be asked to prepare for the test by doing the following:

  • Bring any insurance paperwork that you may need.
  • Avoid wearing any eye makeup that may interfere with eye electrodes.
  • Those who wear contact lenses should bring a case along, as well as some solution since you cannot wear these during the test.
  • Make sure your hair is clean, but avoid any gels or hairspray that may interfere with a scalp electrode.
  • Arrange for someone to drive you home since your eyes will have to be dilated.

During the Test

The test will actually take place in two phases—dark and light.

It will begin with the dark phase, in which dilating drops will be placed in your eyes. For the next half hour or so, your eyes will be covered to help them adapt to the dark.

Numbing drops will go into your eyes, and an electrode will be placed in each one to measure electrical activity in response to light. Not to worry, at worst your eye will feel a little scratchy.

After about 30 minutes, you will be seated facing the machine with the flashing lights. Initially, there will be a single flash here and there and, with time, the flashes will get brighter and you may even be able to see colors.

Then you will move on to the light phase. You will be given about 10 minutes to reacclimate to the light. Then, once again, you will be seated in front of the machine, where you will view flashes of light in a well-lit environment.

After 60–90 minutes the test will be complete.

Post Test

After the test, any electrodes will be removed. It may take time to recover from having your eyes dilated. So, you may wish to have sunglasses on hand, as well as someone to drive you home.

After the Test

Apart from letting your eyes readjust after being dilated, you should quickly be able to resume your activities after the electroretinogram. Do, however, avoid rubbing your eyes for about one hour after the test. Rubbing may cause injury to your cornea, the clear protective dome over your eyes, which may still be slightly numb.

Interpreting Results

Your healthcare provider will be looking at the wave-like patterns of electrical activity of the retina that occur each time the light flashes. If the waves are somewhat delayed or not as large as they should be, your provider will note that damage may have occurred on the retina.

Some conditions that may account for abnormal results include the following:

Keep in mind that there are also some factors that can potentially affect results such as:

  • Patient positioning, such as being seated too far away from the flash can reduce the height of the wave
  • Pupil size
  • Interference elsewhere in the eye, such as a cloudy lens (cataract)
  • Being very nearsighted, which may cause the amplitude of the waves to be reduced
  • Drugs circulating in your system


If it is suspected that your abnormal results are linked to an eye condition, your follow-up care will need to be handled by a specialist. The treatment will depend on the condition diagnosed.

Other Considerations

If after undergoing an electroretinogram you learn that you likely have a retinal issue, it may be helpful to check the results with several specialists who may offer different perspectives. Likewise, if the results appear normal but you are still experiencing unexplained symptoms, it can be worthwhile to seek a second opinion.


An electroretinogram is designed to determine how well the light-sensitive retinal tissue is functioning. This test monitors the electrical activity that occurs in response to flashing lights in both dark and light conditions.

The electroretinogram should take about 60–90 minutes to complete. If any abnormalities are found, these can be discussed with an eye specialist.

A Word From Verywell

The idea of undergoing a test such as an electroretinogram can cause stress. But keep in mind that the test itself is relatively easy to undergo. It can be an important step in diagnosing a condition that can affect your vision. Be sure to ask questions about what the results mean and what treatment options you may have.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Moorfields Eye Hospital National Health Services. Having an electroretinogram.

  2. University of Pittsburgh Medical Center. Electroretinogram.

  3. American Academy of Ophthalmology. Electroretinogram.

  4. University of Michigan Health. Electrophysiology tests for the eyes.

  5. Michigan State University. Flash electroretinogram (ERG).

  6. Wills Eye Hospital. Electroretinogram/multifocal ERG.

  7. University of California San Francisco Health. ERG electrophysiologic testing

By Maxine Lipner
Maxine Lipner is a long-time health and medical writer with over 30 years of experience covering ophthalmology, oncology, and general health and wellness.