Functional topography of rod and cone photoreceptors in macaque retina determined by retinal densitometry

The purpose of this study is to determine the topography of bleaching in rods, middle/long-wavelength (M/L) and short-wavelength (S) cones in the macaque retina by using a modified retinal densitometry technique.

A modified commercial digital fundus camera system was used to measure continuously the intensity of the light reflectance during bleaching with band pass lights in the ocular fundus of three adult Rhesus monkeys (Macaca mulatta) under general anesthesia. The topography of bleaching in rods, M/L-, and S-cones was obtained separately by considering the characteristic time course of the reflectance changes, depending on the wavelengths of light and retinal locations.

The distribution of M/L-cones response had a steep peak at the foveal center and was elongated horizontally. The distribution of rod responses was minimum at the foveal center and maximum along a circular region at the eccentricity of the optic disc. The distribution of S-cone responses was highest at the fovea and was excavated centrally. There was a circular region with the maximal responses at 0.38 to 1.0 degrees from the foveal center.

With the current imaging technique, not only the steep peak of the M/L-cone responses at the fovea, but the ring-shaped distribution of rod responses in the periphery and the central reduction of S-cone response could be determined with good resolution.