1 Electroretinography Kyle Wolpert and Stephen Tsang

Electroretinography is a mainstay of clinical ophthalmic diagnostic testing. The electroretinogram, or ERG, provides an objective, quantitative measure of retinal function and allows the clinician to monitor the function of rod cells, cone cells, and ganglion cells in each eye. It uses electrodes placed on the cornea or adjacent to the orbit to monitor changes in the electrical potential of the eye in response to specific stimuli. Careful manipulation of the stimulus and testing conditions allows the clinician to investigate different cell types and layers of the retina. The ability to distinguish between different cell layers and cell types means that ERGs can be used to discern between myriad inherited retinal disorders and dystrophies that may otherwise prove clinically indistinguishable. Several different types of ERG test provide specific information about the patient’s visual function. The full-field ERG, or ffERG, is the most common form of electroretinographic testing. It provides an assessment of general retinal function and can distinguish between the various cell types, revealing the function of photoreceptors, bipolar cells, ganglion cells and amacrine cells, but cannot provide specific information about individual sectors of the retina. That information is provided by the multi-focal ERG, or mfERG, which measures the response in each of a large number of small sectors, typically either 61 or 103, of the retina. It thus provides a map that allows the clinician to locate specific areas of malfunction. The pattern ERG, or PERG, measures the response to a temporally changing pattern of contrast at a constant level of luminance, providing information about ganglion cells and generalized macular function. The electro-oculogram, or EOG, measures changes in the resting potential of the eye during adaptation to dark and light states, revealing function of the retinal pigment epithelium.