What Is Electroretinography?
An electroretinography (ERG) test, also known as an
electroretinogram, measures the electrical response of the light-sensitive
cells in your eyes.
These cells are known as rods and cones. They
form part of the back of the eye known as the retina. There are around 120
million rods in the human eye and 6 to 7 million cones. The cones are
responsible for the eye’s color sensitivity. They reside mostly in your eye’s
macula. The rods are more sensitive to light than the cones, but they’re not
more sensitive to color.
Why Do I Need an Electroretinography Test?
Your doctor may perform an ERG to determine if you have an
inherited or acquired disorder of the retina, such as:
- retinitis pigmentosa, which is a genetic disease
causing loss of peripheral and night vision
- macular degeneration, which is a loss of vision
due to the death of cells in the macula
- retinoblastoma, which is a cancer of the retina
- retinal separation, which is a detachment of the
retina from the back of the eyeball
- cone rod dystrophy (CRD), which is vision loss
due to impaired cone and rod cells
An ERG may also help your doctor assess your need for retinal
surgery or other types of eye surgery, such as the removal of cataracts.
What Happens During an Electroretinography
The following occurs during an ERG:
- Your doctor will ask you to lie down or sit in a
- They’ll dilate your eyes with eye drops in
preparation for the test.
- Your doctor will place anesthetic drops in your
eyes, which will make them numb.
- They’ll use a device known as a retractor to
hold open your eyelids. This will enable them to carefully place a small
electrode on each eye. The electrodes are about the size of a contact lens.
- Your doctor will attach another electrode to
your skin so that it functions as a ground for the faint electrical signals
made by the retina.
- You’ll then watch a flashing light. Your doctor
will conduct the test in normal light and in a darkened room. The electrode
enables the doctor to measure your retina’s electrical response to light. The
responses recorded in a light room will mainly be from your retina’s cones. The
responses recorded in a darkened room will mainly be from your retina’s rods.
- The information from the electrodes transfers to
a monitor. The monitor displays and records the information. It appears as
a-waves and b-waves. The a-wave is a positive wave that originates
mainly from your eye’s cornea. It represents the initial negative deflection of
a flash of light. The b-wave, or positive deflection, follows. The plot of
the b-wave’s amplitude reveals how well your eye reacts to light.
What Do the Results Mean?
If your results are normal, they’ll show the wave patterns of a
normal eye in response to each flash of light.
Abnormal results may indicate any of the following conditions:
- arteriosclerosis damage to the retina
- congenital retinoschisis, which is a splitting
of layers in the retina
- congenital night blindness
- giant cell arteritis
- retinal detachment
- cone rod dystrophy (CRD)
- certain medications
- vitamin A deficiency
What Are the Risks Associated with an
There are no risks linked to the ERG. You may feel a slight
discomfort during the procedure. The placement of the electrode feels something
like having an eyelash lodged in your eye. Your eyes may feel slightly sore for
a short time after the test.
In very rare cases, some people suffer from a corneal abrasion
from the test. If this happens, your doctor can detect it early and treat it
Monitor your condition after the procedure and follow all
aftercare instructions your doctor gives you. If you have continued discomfort
following an ERG, you should contact the doctor who performed the test.
What Happens After an Electroretinography
Your eyes will likely feel sensitive after the test. You should
avoid rubbing your eyes for up to an hour after the test. This may cause
corneal damage because they’ll still be numb from the anesthetic.
Your doctor will discuss your results with you. They may order
further tests to assess your eye. You may need surgery if you have a disorder
such as retinal separation or trauma.
Your doctor may prescribe you medication to treat other retinal