Patients referred to University of Maryland Electrophysiology Laboratory receive testing that goes beyond a general eye exam. Visual function testing will provide you with detailed results and offer you the latest approaches to treat your eye condition.

Dr. Mary A. Johnson, a specialist in vision with over 20 years of experience in clinical electrophysiology, will meet with you to collect a thorough background on your eye experiences. Dr. Johnson has extensive experience diagnosing rare eye diseases.

Tests Available at the University of Maryland Electrophysiology Laboratory

We perform pain-free testing in the University of Maryland Electrophysiology Laboratory.

Electroretinogram (ERG)

The electroretinogram, or ERG, is like an EKG for the eye. During this test, we will record responses from the nerves in the eye, which gives us very sensitive information about how the eye is working. The test takes a few minutes, but we will need time to dilate your pupils and let your eyes get adjusted to the dark. This test involves putting some numbing drops in your eyes then placing contacts on your eyes. We will flash several different types of lights for a few minutes. We typically record from both eyes at the same time. This test takes approximately one hour to complete.

Multifocal ERG

If you are here for a multifocal ERG, you will not need to be dilated or dark-adapted. This test uses the same contact lens as the ERG test, but instead of flashing lights, you will be looking at a television screen containing black and white checks that turn on and off. The test takes only four minutes an eye, and we will record from each eye individually. This test takes approximately one hour to complete.

Visual Evoked Potential (VEP)

The visual evoked potential, or VEP, measures how information from the eye gets to the brain. To do this test, we paste wires on the front and back of your head. You will look at a television screen that shows black and white checks. If you wear glasses, please be sure to bring them with you. This test takes approximately one hour to complete.

Electro-Oculogram (EOG)

The electro-oculogram, or EOG, measures how well a layer of cells supporting the retina is working. In this test, we paste wires on either side of each eye and have you look at two lights that are alternating back and forth. You will look at these lights for the first 15 seconds of every minute for 35 minutes. This test takes approximately one hour to complete.

Color Vision Tests

We do a variety of color vision tests. All of them involve sorting caps with different colored tops. The Farnsworth-Munsell 100-hue color vision test takes between 30 minutes and an hour for most people. The desaturated Lanthony D-15 test and Roth-28 test are much shorter, each taking 15 to 30 minutes.

Location Information

The Visual Function/Electrophysiology Laboratory is located at the corner of Redwood and Paca Streets.

419 W. Redwood, Suite 420
Baltimore, MD 21201


Parking is available at the Grand Garage on Paca St., one and one-half blocks north of the lab on the right.

Contact Us

For more information or to schedule an appointment, please call 667-214-1111.