Clinical Visual Electrophysiology: A Tool for Studying Inherited Retinal Disorders

Clinical visual electrophysiology is used to assess visual function and differentiate between acquired and inherited retinal diseases (IRD). This chapter will describe electroretinogram (ERG) and summarize International Society for Clinical Electrophysiology of Vision standards for ERG as well as discuss the uses of ERGs for identifying IRDs. ERG uses electrodes placed on the cornea or skin of the adnexa to measure the retina’s electrical activity in response to light stimulus. This stimulus consists of brief flashes of light presented in a full-field cupola during four dark adapted and two light adapted conditions. ERG measures activity in the inner and outer retinal layers from the rods and cones during the light and dark adopted conditions. There is substantial variability in the phenotypic expression of different genes responsible for IRDs. However, ERGs, in combination with ophthalmic exams and patient history, can aid in identification of numerous IRDs. IRDs can be identified based on whether they affect the rod pathways and evidence abnormalities during dark-adapted ERGs and/or affect the cone pathway and evidence abnormalities during light-adapted ERGs. Abnormalities in the rod pathway are characteristic of retinitis pigmentosa, the most common IRD, and congenital stationary night blindness. ERG’s ability to discern whether the central or peripheral function is affected is useful in identifying diseases that primarily affect central retinal functioning such as cone-rod dystrophies and cone dysfunction syndromes.