Electroretinography is a test to measure the electrical response of the eye's light-sensitive cells, called rods and cones.

While you are comfortably seated in a chair, the health care provider places numbing drops into your eyes, so you do not feel pain during the test. Your eyes are then propped open and an electrical sensor (electrode) is placed on each eye.

The electrode measures the electrical activity of the retina in response to light. A light flashes, and the electrical response travels from the electrode to a TV-like screen, 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.

No special preparation is necessary for this test.

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

This test is done to detect disorders of the retina. It is also useful in determining if retinal surgery is recommended.

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

The following conditions may cause abnormal results:

• Arteriosclerosis
• Congenital night blindness
• Congenital retinoschisis
• Giant cell arteritis
• Iron poisoning
• Mucopolysaccharidosis
• Retinal detachment
• Rod-cone dystrophy (retinitis pigmentosa)
• Vitamin A deficiency

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

You should not rub your eyes for an hour after the test, as this could injure the cornea. Your doctor will discuss with you the results of the test and what it means for you.