Electrophysiology for ophthalmologist (A practical approach)

The article deals with the basic understanding of electrophysiological tests in clinical practice. Electrophysiological tests involves assessing the function of the rod-cone system and proximal visual pathway. Visual evoked potential (VEP) is performed to assess the function of the proximal optic nerve. Electro-oculogram (EOG) is used to study the photoreceptor-RPE junction. Electroretinogram (ERG) is used to assess the function of photoreceptor (a-wave) and the inner retina (b-wave). Pattern ERG is helpful to study the macular cone function and ganglion cell function. The a-wave in ERG is diagnostic of rod-cone or cone-rod dystrophy. The amplitude of b-wave in ERG helps us to distinguish inner retinal dysfunction from photoreceptor dysfunction. Hence ERG is not only helpful in making a diagnosis but is also helpful in studying the prognosis of the disease which eventually helps in counseling the patient. Pattern ERG when used in conjunction with pattern VEP helps to pinpoint the cause of an unexplained loss of vision. Multifocal ERG studies the focal responses at the posterior pole within the arcades. The most important use of a multifocal ERG is in the early detection of hydroxychlroquine toxicity. Visual acuity assessments with sweep VEP, focal ERG and multifocal VEP are the newer developments in electrophysiology