Patients referred to this laboratory by their doctors often have problems with their vision that cannot be explained by an eye exam given by an eye doctor. In most electrophysiology labs across the country, if your doctor wants a test done, a technician will do the test and report the results back to the doctor.

At the University of Maryland Electrophysiology Laboratory, you will be seen personally by Dr. Mary A. Johnson, a specialist in vision with over 20 years of experience in clinical electrophysiology. She will ask you questions about the vision problems you are having and then will perform the test(s). Because she is also a scientist, she can use her knowledge of cutting-edge research to help understand why you are having trouble seeing. Because of her clinical experience, she has seen many rare cases of eye disease so that she can often diagnose even very unusual problems. Because she cares about people, she takes the time to listen to you to fully understand your problems.

Tests Available at the University of Maryland Electrophysiology Laboratory

There are several tests available in the University of Maryland Electrophysiology Laboratory. All of the tests are painless.

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 itself only takes a few minutes, but because we have to dilate your pupils and get you used to the dark, plan on being here for an hour. To do the test, we put some numbing drops in your eye and then put on a contact lens (the numbing drops are so you will not feel the contact lens). Then we will flash several different types of lights for a few minutes, and the test will be over. We typically record from both eyes at the same time.

Multifocal ERG

If you are here for a multifocal ERG, you will not need to be dilated or dark-adapted, but we will record from each eye individually. This test uses the same contact lens as the other 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 itself takes only four minutes an eye, but your visit will take a little less than an hour.

Visual Evoked Potential (VEP)

The visual evoked potential, or VEP, measures how the information from the eye gets to the brain. To do this test, we paste wires on the front and back of your head, and have you look at a television screen that will show black and white checks. As with the other tests, expect to be here for about an hour. If you wear glasses, please be sure to bring them with you.

Electro-Oculogram (EOG)

The electro-oculogram, or EOG, measures how well a layer of cells that supports the retina in the back of the eye is working. In this test, we paste wires on either side of each eye, and have you look back and forth between two lights that are alternating back and forth. You will be looking at these lights for the first 15 seconds of every minute for 35 minutes. So, plan on being here for about an hour.

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 total visit time.

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., 1 and ½ blocks north of the lab on the right.

Contact Us

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