Visual Function Testing Service

Electroretinogram (ERG)

  • Dilation is required for this test.
  • Purpose of the test – The ERG is an electrical response of the cells of the retina to a flash of light. The responses obtained from the ERG can provide objective information about the function of your retina.
  • Test duration – Approximately 1 hour and 30 minutes. Thirty minutes of this estimate is needed to assure proper dilation. Therefore, if you have already been dilated during the course of a previous test or examination, this estimate will be about thirty minutes shorter.
  • Testing procedure – After being dilated, you will be placed in a darkened room for thirty minutes in order to dark adapt the cells that make night vision possible. After numbing your eyes with a drop of topical anesthetic, a special contact lens will be placed on your cornea. Lights of different colors and intensities will be flashed off the inside of the bowl that you will be looking into. This is not a painful procedure but you will be asked to remain very still for a period as long as 45 minutes.
  • What you should do before coming – Contact lens wearers should wear spectacles on the day of ERG testing. You should also make transportation arrangements for leaving our office after the test, because your pupils will be dilated and your vision will not be perfectly clear for another 2-3 hours.
  • Restrictions after testing –
    • Because you will be dilated for this test, it is generally recommended that you not drive afterward until all the effects of dilation have worn off. These effects include “fuzzy vision”, increased glare and brightness, increased sensitivity to light, and difficulty reading within arm’s length.
    • Swimming is discouraged for the remainder of the day.
    • Generally, you should experience no visual difficulties should you decide to return to your indoor job unless close-up tasks are a requirement. Contact lens wearers should wear their spectacles for the remainder of the day.

Electro Oculogram (EOG)

  • Dilation is required for this test.
  • Purpose of the test – This test measures the electrical changes within one layer of the retina which occur during dark-adaptation and light-adaptation. The EOG is used to detect and differentiate among several types of retinal dystrophies.
  • Test duration – Approximately 1 hour and 30 minutes. Thirty (30) minutes of this estimate is needed to assure proper dilation. Therefore, if you have already been dilated during the course of a previous test or examination, this estimate will be thirty minutes shorter.
  • Testing procedure – While your eyes are dilating, the skin near the corners of each eye will be cleaned with an alcohol solution and then 4 small electrodes will be taped in position. Another electrode will be placed behind your ear. You’ll be positioned in front of an instrument and you’ll be asked to follow two alternately flashing lights with your eyes for 15 seconds out of each minute for a total test time of 36 minutes. This test can be boring because of the requirement to remain still and also because of the monotonous yet important task.
  • What you should do before coming – Contact lens wearers should wear spectacles on the day of EOG testing. You should also make transportation arrangements for leaving our office after the test.
  • Restrictions after testing
    • Because you will be dilated for this test, it is generally recommended that you not drive afterward until all the effects of dilation have worn off. These effects include “fuzzy vision”, increased glare and brightness, increased sensitivity to light, and difficulty reading within arm’s length.
    • Generally, you should experience no difficulties should you decide to return to your indoor job unless close-up visual tasks are a critical part of your job. Contact lens wearers should wear their spectacles for the remainder of the day.

Visual Evoked Potential (VEP) or Visual Evoked Response (VER)

  • You MUST NOT be dilated for this test.
  • Purpose of the test – The Visual Evoked Potential is a measure of the flow of electrical information between the eye and the brain. This test is very similar to the more familiar test called the EEG or electroencephalogram and is used to detect disturbances involving the visual pathway beyond the outer and middle part of the retina.
  • Test Duration – Approximately 1 hour.
  • Procedure – Several places on your scalp will be thoroughly cleaned with an alcohol solution in preparation for the placement of surface electrodes. A water soluble paste is used along with tape to attach these electrodes to several places on your scalp and behind your ears. It is not necessary to shave your scalp or cut your hair to apply the electrodes. After instrumentation, you’ll be asked to watch, steadily, a fixed spot presented against a checkerboard background on a television screen, all the while remaining very still. Later you’ll be asked to observe a flashing light. A few patients report feeling fatigued after this test because of the requirement to remain still and attentive for periods as long as 1/2 hour.
  • What you should do before coming – For this test it is very important to bring the best possible distance (driving) correction with you. Most of the time, your best distance correction will be your most recent eyeglasses or contact lens prescription. Prescription sunglasses are not acceptable substitutes for regular spectacles but “Photo Grey” spectacles are OK. If you have a recent prescription for spectacles but have not yet obtained the spectacles, then bring the prescription itself. If in doubt, please ask your ophthalmologist or your optometrist prior to your VEP appointment. Because your hair will usually be disheveled after testing, you might also bring whatever hair preparation or implements you normally use.
  • Restrictions after testing – None.

Dark Adaptometry (DA)

  • Dilation is required for this test.
  • Purpose of the test – The purpose of this test is to measure and record the change in retinal sensitivity that occur during the first 1/2 hour of darkness immediately following exposure to an adapting light. This test helps distinguish between benign complaints of poor night vision versus diseases of the retina.
  • Test duration – Approximately 1 hour and 30 minutes. Thirty (30) minutes of this estimate is needed to assure proper dilation. Therefore, if you have already been dilated during the course of a previous test or examination, this estimate will be thirty minutes shorter.
  • Procedure – After being dilated, you will be positioned near an internally illuminated bowl, and will place your head at the entrance of this bowl and observe the light reflected off the surface of the bowl for 8 minutes. During this time, you will be asked to keep your eyelids widely open. After turning off the adapting light, the brightness of another very dim spot of light will be gradually increased until you signal with a buzzer that you are able to see it. After detection of this test light, the brightness will be gradually decreased until it is once again invisible. This cycle is repeated for 30 minutes per eye, making the total duration of the test about 1.5 hours including dilating time.
  • What you should do before coming – Contact lens wearers should wear spectacles on the day of dark adaptation testing. You should also make transportation arrangements for leaving our office after the test.
  • Restrictions after testing
    • Because you will be dilated for this test, it is generally recommended that you not drive afterward until all the effects of dilation have worn off. These effects include “fuzzy vision”, increased glare and brightness, increased sensitivity to light, and difficulty reading within arm’s length.
    • Generally, you should experience no difficulties should you decide to return to your indoor job unless close-up visual tasks are a critical part of your job.

Color Vision Battery

  • Dilation is NOT required for this test.
  • Purpose of this test – Color vision testing is used to quantify color vision loss and to differentiate between hereditary versus acquired defects. This test is often done in conjunction with other tests to provide additional information when problems involving the optic nerve and/or retina are suspected.
  • Test Duration – Approximately 1 hour.
  • Procedure – Color vision is tested in several ways: by arranging a long series of colored caps; identifying camouflaged numbers on a card; matching circles of color pigments to a background color; and by adjusting two spectrally produced colors to achieve a match. The choice of which color vision tests used during your visit is dependant upon your diagnosis or reason for being referred.
  • What you should do before coming – Please bring your best distance vision and reading vision prescription, spectacles or contact lenses. Do not use tinted contact lenses on the day of testing.
  • Restrictions after testing – None.

Contrast Sensitivity and Glare Testing

  • Dilation is NOT required for this test.
  • Purpose of this test – Glare testing is used to quantify and follow the effects of early cataract formation and other conditions of the eye causing light to be scattered. Contrast sensitivity testing is typically used to detect and follow conditions affecting the optic nerve.Test Duration – Approximately 1 hour.

Procedure – Currently there are 5 methods of testing your contrast sensitivity, but in all of these methods you will be asked to indicate your perception of some sort of faint visual pattern. In some tests this pattern will be shown to you on a wall chart or television screen while in other tests this pattern might be projected into your eye like a movie projector.

  • What you should do before coming – Please bring your best distance vision prescription, spectacles or contact lenses.
  • Restrictions after testing – None