Electrophysical Testing

An electroretinogram, often shortened as ERG, is a diagnostic exam used to measure the electrical responses of the retina to various patterns of light. Offering a perspective for the doctor to assess the functional health of the retina, the ERG connects various electrodes and adapters to the patient to determine responses to various light flashes.

Setting up the ERG

Dark adapt

In order to perform a comprehensive ERG examination, the patient has to be fully dilated and dark-adapted. The patient is dilated and then situated in a dark room with patches over the eyes to allow adaptation to complete darkness. This process allows the eyes to become fully sensitized to light.

Connecting the electrodes

A total of three electrodes are connected to the patient. The first electrode is connected to the ear to serve as a ground electrode. The second electrode is a reference electrode and is attached to the forehead. Both of these electrodes serve to maximize the accuracy and precision of our test. The third electrode, the working electrode, consists of a thin silver-nylon fiber that is to be placed in the bottom eye socket. Upon set-up, these electrodes are connected to an adapter that ultimately records responses from the patient.

Light adapt

In the midst of the examination, the patient is to be light-adapted after completion of the first portion of the exam which required dark adaptation. Light adaptation, in contrast to dark-adaptation, requires the patient to observe bright light for a duration of ten minutes to achieve desensitization of light for the eyes. Upon doing so, this allows for an accurate measure of the cones in the retina.

Performing the test

Overall, the test consists of a series of flashes of different intensity to measure responses. Upon connecting all electrodes, the patient is to stare directly at a spot directed by the technical specialist administering the exam. The patient is then to observe a flash of light which will then transmit a response that will be picked up by the electrode automatically. While doing so, the patient must be as still as possible. This ensures the prevention of any outside noises interfering with our test results. A series of flashes of varying intensity will be shown to the patient and assessed by the computer. Following shortly thereafter, the patient is to be light adapted and subjected to a several more light flashes.

What to expect

The total time necessary to complete this diagnostic exam may take approximately 50 to 70 minutes, largely due to the amount of time needed for setups and preparations. Precautions to take into consideration are avoiding squinting and excessive ocular movements which may interfere with the integrity of the results of the test.


A multi-focal electro-retinogram, or mf-ERG, allows the physician to obtain electrical responses from a specific portion of the retina, usually the macula. Allowing the physician functional assessment of the macula, the mfERG is used in collaboration with other examinations of a patient’s macula to diagnose and plan a treatment.