Interocular symmetry of parafoveal photoreceptor cone density distribution.

PURPOSE To investigate the variation and symmetry of cone density distribution along the nasal and temporal retina of fellow eyes. METHODS An adaptive optics retinal camera (rtx1; Imagine Eyes) was used to obtain images of the parafoveal cone mosaic in 20 healthy subjects. Cone density was estimated at 250, 420, 760, and 1,300 μm eccentricity from the fovea along the nasal and temporal retina of both eyes in each subject. The coefficient of variation and the intraclass correlation coefficient were used to calculate the variation and absolute agreement of cone density between the same retinal eccentricity locations of fellow eyes, respectively. RESULTS A considerable variation of cone density between subjects was found at all eccentricities along the nasal and temporal retina (intersubject coefficient of variation ≥ 11%, P < 0.001). The intrasubject variation of cone density was, however, moderate (coefficient of variation ≤ 13% in 95% of the subjects); a high agreement was, on average, found between the cone density estimates at the same eccentricity along the nasal and temporal retina of fellow eyes (intraclass correlation coefficient ≥ 0.86, P < 0.001). CONCLUSION Cone density follows a symmetrical distribution between fellow eyes. A systematic distribution of parafoveal cones between fellow eyes may provide an anatomical basis for the involvement of the photoreceptor layer in the first step of binocular spatial sampling.