Visual Electrophysiology

Test length 

This test is approximately 90 minutes (including pupil dilation).

Test definition

The electroretinogram (ERG) is a widely use visual electrophysiological test of retinal function. It measures the electrical activity of the retinal cells in response to flashes of light.

Test procedure

The ERG is recorded with 2 corneal, non-contact, electrodes (DTL fiber electrodes) placed in the conjunctival sac of each eye, and 3 gold cup electrodes taped onto the forehead and onto the right and left temples. Flashes of lights from a stimulator (ganzfeld) are presented to the patient with the room lights on and off.

Other pertinent information

Before the ERG test, drops will be placed in each eye to dilate (enlarge) the pupils, which causes blurred vision and sensitivity to light. The pupils may be dilated for 6-24 hours.

Patients should bring a pair of sunglasses to wear after the test due to light sensitivity. We do not recommend that patients drive after the test and suggest patients arrange alternative transportation

Typically, ERGs can be recorded on patients of all ages.

Test length

This test is approximately 60 minutes (including pupil dilation).

Test definition

The multifocal electroretinogram (mfERG) is a visual electrophysiological test of macular function. It measures the electrical activity of the macular retinal cells.

Test procedure

The mfERG is recorded with 2 corneal, non-contact, electrodes (DTL fiber electrodes) placed in the conjunctival sac of each eye, and 3 gold cup electrodes taped onto the forehead and onto the right and left temples. An array of hexagonal elements is presented on a computer screen to the patients with the room lights on.

Other pertinent information

Before the mfERG test, drops will be placed in each eye to dilate (enlarge) the pupils, which causes blurred vision and sensitivity to light. The pupils may be dilated for 6-24 hours.

Patients should bring a pair of sunglasses to wear after the test due to light sensitivity. We do not recommend that patients drive after the test and suggest patients arrange alternative transportation.

The mfERG requires full cooperation from the patient, and therefore, patients must be 10 years of age or older.

Test length

This test is approximately 60 minutes.

Test definition

The visual evoked potential (VEP) provides important diagnostic information regarding the functional integrity of the visual system. It measures the electrical activity of the brain that is produce in response to an external visual stimulus. The most widely used stimuli are flashes of light (FVEP) or checkerboards (PVEP).

Test procedure

The VEP is recorded with 3 gold cup electrodes placed on the back of the head (held in place with a bandana) and 2 gold cup electrodes taped onto the forehead and onto the left temple. Typically, the VEPs are recorded with both eyes open and with a patch placed over each eye to test the eyes separately. Flashes of lights from a stimulator (FVEP) and checkerboards from a computer screen (PVEP) are presented to the patient with the room lights on.

Other pertinent information

This test does not require any eye drops.

The VEPs can be performed on patients older than 6 months of age. Typically, FVEPs do not required full cooperation of the patient and can be performed at 6 months, however, the PVEPs requires full cooperation, and therefore, patients should be at least 2-5 years of age to perform the test.

The PVEP should be performed with corrected vision (glasses or contacts).

Patients who have weaves, cornrows, dreadlocks, or wigs must take them out or off. The VEP required placing electrodes on the surface of the scalp on back of the head

Test length

This test is approximately 90 minutes (including pupil dilation).

Test definition

The electro-oculogram (EOG) is a visual electrophysiological test which reflects the integrity of the retinal pigment epithelium. It measures the outer retinal cells and retinal pigment epithelium cells function.

Test procedure

The EOG is recorded with 4 small gold cup electrodes taped on each side of the nose and on each side of the temple. The patient looks into a white globe stimulator (ganzfeld) and follows two alternating red lights for 15 seconds every minute for a total of approximately 45 minutes. Part of the test requires that all the lights in the room are turned off.

Other pertinent information

Before the EOG test, drops will be placed in each eye to dilate (enlarge) the pupils, which causes blurred vision and sensitivity to light. The pupils may be dilated for 6-24 hours.

Patients should bring a pair of sunglasses to wear after the test due to light sensitivity. We do not recommend that patients drive after the test and suggest patients arrange alternative transportation

The EOG requires full cooperation from the patient, and therefore, patients must be 10 years of age or older.

Test length

This test is approximately 15 minutes.

Test definition

The Farnsworth Dichotomous Test (Panel D-15) measures color vision.

Test procedure

The patient will view multiple colors (15 different ones) and will be ask to place the colors in order of similarity.Typically, the D-15 test is recorded with both eyes open and with a patch placed over each eye to test the eyes separately.

Other pertinent information

This test does not require any eye drops.

The D-15 test requires full cooperation from the patient, and therefore, patients must be 5 years of age or older.

The D-15 test should be performed with corrected vision (glasses or contacts).

Test length

This test is approximately 60 minutes.

Test definition

The Farnsworth 100 Hue Test (F-100) measures color vision.

Test procedure

The patient will view multiple colors (100 different ones) and will be ask to place the colors in order of similarity.Typically, the F-100 test is recorded with both eyes open and with a patch placed over each eye to test the eyes separately.

Other pertinent information

This test does not require any eye drops.

The F-100 test requires full cooperation from the patient, and therefore, patients must be 10 years of age or older.

The F-100 test should be performed with corrected vision (glasses or contacts).

Test length

This test is approximately 30 minutes

Test definition

The Preferential Looking Technique (PLT) is a visual acuity test that provides a quantitative assessment of visual acuity in preverbal and/or nonverbal children, who are unable to provide reliable responses verbally.

Test procedure

The PLT involves having the patient watch a series of handheld cards which contain black and white stripes (grating) on one side of the card. The examiner observes the patient’s eye and head movements in response to the cards to determine the patient’s visual acuity. Typically, the PLT is performed with a patch placed over each eye to test the eyes separately.

Other pertinent information

This test does not require any eye drops.

The PLT should be performed with corrected vision (glasses or contacts).

Test length

This test is approximately 15 minutes

Test definition

The Contrast Sensitivity Function (CFS) measures the ability to detect luminance contrast and is an effective tool for isolating visual problems such as cortical problems, optic atrophy, glaucoma cataracts, optic neuritis, refractive errors, macular anomaly, and other visual anomalies..

Test procedure

The CSF test involves having the patient watch a series of four (4) rows of sine-wave gratings at a distance of 8 feet. The patient has to identify in each row if the grating is located the higher or lower circle.  Typically, the CSF test is performed monocularly with a patch placed over each eye to test the eyes separately.

Other pertinent information

This test does not require any eye drops.

The CSF should be performed with corrected vision (glasses or contacts).