Electrophysiological responses related to the pigment epithelium and its interaction with the receptor layer.

The standing potential (SP) of the eye is generated mainly at the apical surface of the pigment epithelium, where tight junctions between adjacent cells create a high resistance membrane. It can be recorded indirectly by means of the electrooculogram (EOG) or directly by recording between electrodes connected to the cornea and the forehead. Changes in illumination provoke slow SP changes in the form of damped oscillations with a frequency of about 2/hour. These oscillations are abolished or substantially reduced in pigment epithelial diseases, such as retinitis pigmentosa and vitelline macular degeneration. The c-wave of the electroretinogram (ERG) represents the hyperpolarization mainly of the apical membrane of the pigment epithelial cells that occurs in response to a decrease in potassium ion concentration in the extracellular space of the receptor layer induced by light stimulation. When repeatedly recorded the amplitude of the c-wave oscillated with time in the same way as the SP. The c-wave is abolished or markedly reduced in pigment epithelial disorders. The negative h-wave of the off-ERG shows such extensive similarities to the c-wave of the on-ERG that it seems to represent the reversal of the processes in the pigment epithelium - receptor complex underlying the c-wave.