Clinical electrophysiology of the retinal pigment epithelium.

There is no ideal electrophysiological test for retinal pigment epithelial (RPE) function. The light-induced responses (EOG, c-wave, fast oscillation) that require photoreception are not pure RPE signals, and even the widely-used EOG has not been associated with any specific physiological disturbance of the RPE or retina. The discovery of non-photic RPE responses (hyperosmolarity, acetazolamide and bicarbonate) has enhanced the possibility of finding tissue-specific RPE tests, but these responses have yet to be correlated with specific RPE functional activity or pathology. We may face a dilemma in our search for RPE tests, insofar as electrophysiology measures membrane changes, but RPE membrane activity is related only indirectly to many functions of the RPE cell. These concerns notwithstanding, RPE electrophysiology can be a valuable clinical tool if one accounts for the physiological limitations and assets of the procedures.