Variations in the cone packing density with eccentricity in emmetropes

Aim To describe the parafoveal cone arrangement in emmetropic subjects and its variations with eccentricity, meridians and change in axial length in Indian eyes. Methods We imaged 25 subjects using compact adaptive optics (AO) retinal camera prototype, the rtx1. Imaging was done at 1, 2, and 3 degrees eccentricity from the fovea in four meridians: nasal, temporal, superior, and inferior. Results A statistically significant drop in the cone packing density was observed from 2 to 3 degrees (2 degrees eccentricity = 25 350/mm(2) (5300/mm(2), 8400-34 800/mm(2)) 3 degrees eccentricity = 20 750/mm(2) (6000 mm(2), 9000- 33 670/mm(2))) P<0.05. The spacing correspondingly increased with increase in distance from the fovea (2 degrees eccentricity = 6.9 mm (0.70 mm, 5.95- 11.6 mm)) and 3 degrees eccentricity = 7.80 mm (1.00 mm, 6.5- 13.5 mm) P<0.05. As the axial length increases, the cone density significantly decreases. Interocular variations were noted. Conclusion With the advent of AO, visualization at the cellular level is now possible. Understanding the photoreceptor mosaic in the parafoveal space in terms of its density, spacing, and arrangement is crucial so as to detect early pathology and intervene appropriately. Newer therapeutic modalitites that are targeted at the cellular level like yellow micropulse laser, stem cells, gene therapy and so on may be better monitored in terms of safety and efficacy.