Electroretinography (ERG) is an eye test that is performed to study hereditary and acquired disorders of the retina, including partial and total color blindness (achromatopia), night blindness, retinal degeneration, and detachment of the retina in cases in which the ophthalmoscopic view of the retina is prohibited by some opacity, such as vitreous hemorrhage, cataracts, or corneal opacity. When these disorders exclusively involve either the rod system or the cone system to a significant degree, ERG shows corresponding abnormalities.

For this test, an electrode is placed on the eye to obtain the electrical response to light. When the eye is stimulated with a flash of light, the electrode records potential (electric) change that can be displayed and recorded on an oscilloscope. ERG is indicated when surgery is considered in cases of questionable retinal viability.

1. Have the patient hold eyes open during the procedure.

2. Instill topical anesthetic eye drops.

3. Place bipolar cotton wick electrodes, saturated with normal saline, on the cornea.

4. Use two states of light adaptation to detect rod and cone disorders along with different wavelengths of light to separate rod and cone function. Normally, the more intense the light, the greater the electrical response.

   1. Room (ambient) light

   2. Room darkened for 20 minutes and then a white light is flashed

   3. Bright flash (In cases of trauma, when there is vitreous hemorrhage, a much more intense flash of light must be used.)

5. Use chloral hydrate or a general anesthesia for infants and small children who are being tested for a congenital abnormality.

6. Tell the patient that total examining time is about 1 hour.

1. Changes in ERG are associated with:

   1. Diminished response in ischemic vascular diseases, such as arteriosclerosis and giant cell arteritis

   2. Siderosis (poisoning of the retina when copper is embedded intraocularly [this is not associated with stainless steel foreign bodies])

   3. Drugs that produce retinal damage, such as chloroquine and quinine

   4. Retinal detachment

   5. Opacities of ocular media

   6. Decreased response, such as in vitamin A deficiency or mucopolysaccharidosis

2. Diseases of the macula do not affect standard ERG. Macular disorder can be detected using a focal ERG.

Pretest Patient Care

1. Explain the purpose and procedure of the test. For the most part, the patient will experience little or no discomfort. Explain that the electrode may feel like an eyelash in the eye.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Normal

• Normal A and B waves