Electroretinography

Alternative names
ERG

Definition
Electroretinography is a test to measure the electrical response of the eye’s light-sensitive cells (rods and cones). Electrodes are placed on the cornea and the skin near the eye.

How the test is performed
While you are comfortably seated in a chair, anesthetic drops are placed in your eyes, causing them to become numb. Your eyes are then propped open and an electrode is placed on each eye. The electrode measures the electrical activity of the retina in response to light. The information from the electrode goes to a monitor, where it can be viewed and recorded. The normal response pattern has waves called A and B.

The doctor will take the readings in normal room light and then again in the dark, after allowing 20 minutes for your eyes to adjust. A light is flashed, and the electrical response to the flash is recorded.

How to prepare for the test
No special preparation is necessary for this test.

For infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics:

     
  • infant test or procedure preparation (birth to 1 year)  
  • toddler test or procedure preparation (1 to 3 years)  
  • preschooler test or procedure preparation (3 to 6 years)  
  • schoolage test or procedure preparation (6 to 12 years)  
  • adolescent test or procedure preparation (12 to 18 years)

How the test will feel
The probes that rest on your eye may feel like an eyelash. The test takes about one hour to perform.

Why the test is performed
Both hereditary and acquired disorders of the retina can be evaluated with this test. It is also useful in determining if retinal surgery is recommended.

Normal Values
Normal test results will show a normal A and B pattern in response to each flash.

What abnormal results mean
Decreased electroretinography values may indicate any of the following:

     
  • arteriosclerosis  
  • giant cell arteritis  
  • mucopolysaccharidosis  
  • retinal detachment  
  • siderosis (iron poisoning)  
  • Vitamin A deficiency

What the risks are
The cornea may get a superficial scratch from the electrode. Otherwise, there are no risks associated with this procedure.

Special considerations
You should not rub your eyes for an hour after the test, or you may injure the cornea.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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