Fractional recording and component analysis of primate LERG: separation of photoreceptor and other retinal potentials

The local electroretinogram, as obtained with a single micro electrode in the rhesus monkey fovea is known to be the sum of a number of components. This paper shows how the receptor component may be isolated from the LERG by using a bipolar micro electrode that records the potential across the outer segments of the foveal cones. A component analysis of the single electrode LERG, performed at a number of electrode depths in the retina, yields four components: a receptor-, b-, dc- and slow component. The latter has not been reported previously in the monkey and it is proposed that this is the slow PIII of the primate retina. The amplitude-depth profiles of the four components show why the receptor component may be isolated by fractional recording. The recording area of a bipolar electrode is 10 times smaller than that of a monopolar electrode. Contribution of rods to the responses is often present in the dark adapted foveal LERG but is absent in fractional records from the central fovea. The infusion of sodium aspartate in the eye abolishes the b-component, but does not affect the slow component. Aspartate produces, however, such further complexities that the method seems not suitable for isolation of the receptor potential in the intact primate eye.