Most electrophysiologic tests use evoked potential techniques in which a controlled stimulus is used to evoke an electrophysiologic response. Different techniques can be used to assess the function of the majority of the visual system, extending from the retinal pigment epithelium (RPE) to the primary visual cortex. Dysfunction discovered at one level usually signals abnormalities in another; for example, an abnormal cortical response to a pattern visual stimulus could reflect an uncorrected refractive error, maculopathy, optic neuropathy, primary dysfunction of the posterior visual pathways, or other conditions.
Electrophysiologic testing provides objective measures of visual system function, which are interpreted in conjunction with structural imaging data; normal structure should not be assumed to mean normal function. In addition, in order to accurately interpret the data obtained during electrophysiologic testing, the clinician needs to know the origin of the signals to be able to relate the findings from a particular patient’s test to the underlying pathophysiology. Although this chapter does not provide instructions for a comprehensive diagnostic review, the principles of localization in the examples included here may be applicable to other disorders. In addition to diagnostic uses, electrophysiologic data are used in objective monitoring, either of disease progression or the efficacy of treatment, or as both an outcome measure and an index of safety in the evaluation of novel therapeutic interventions.
A thorough patient history and careful ophthalmic examination helps the clinician determine the most appropriate tests to employ; those tests should then be performed using standardized protocols. The International Society for Clinical Electrophysiology of Vision (ISCEV) publishes minimum standards for performing the routine tests, thus enabling meaningful interlaboratory comparison and literature searches. Many laboratories, particularly those with a strong research interest, use more complex test protocols but also always include the standard responses. The International Federation for Clinical Neurophysiology has also published guidelines for visual system testing, which incorporate suggested test protocols based on patient symptoms.
Fishman GA, Birch DG, Holder GE, Brigell MG. Electrophysiologic Testing in Disorders of the Retina, Optic Nerve, and Visual Pathway. 2nd ed. Ophthalmology Monograph 2. San Francisco: American Academy of Ophthalmology; 2001.
Holder GE, Celesia GG, Miyake Y, Tobimatsu S, Weleber RG; International Federation of Clinical Neurophysiology. International Federation of Clinical Neurophysiology: recommendations for visual system testing. Clin Neurophysiol. 2010;121(9):1393–1409.
International Society for Clinical Electrophysiology of Vision. Standards, recommendations and guidelines. www.iscev.org/standards/index.html. Accessed March 15, 2018.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.