Cone photoreceptor definition on adaptive optics retinal imaging

Aims To quantitatively analyse cone photoreceptor matrices on images captured on an adaptive optics (AO) camera and assess their correlation to well-established parameters in the retinal histology literature. Methods High resolution retinal images were acquired from 10 healthy subjects, aged 20-35 years old, using an AO camera (rtx1, Imagine Eyes, France). Left eye images were captured at 5 degrees of retinal eccentricity, temporal to the fovea for consistency. In three subjects, images were also acquired at 0, 2, 3, 5 and 7 degrees retinal eccentricities. Cone photoreceptor density was calculated following manual and automated counting. Inter-photoreceptor distance was also calculated. Voronoi domain and power spectrum analyses were performed for all images. Results At 5 degrees eccentricity, the cone density (cones/mm(2) mean +/- SD) was 15.3 +/- 1.4x10(3) (automated) and 13.9 +/- 1.0x10(3) (manual) and the mean inter-photoreceptor distance was 8.6 +/- 0.4 mu m. Cone density decreased and inter-photoreceptor distance increased with increasing retinal eccentricity from 2 to 7 degrees. A regular hexagonal cone photoreceptor mosaic pattern was seen at 2, 3 and 5 of retinal eccentricity. Conclusions Imaging data acquired from the AO camera match cone density, intercone distance and show the known features of cone photoreceptor distribution in the pericentral retina as reported by histology, namely, decreasing density values from 2 to 7 degrees of eccentricity and the hexagonal packing arrangement. This confirms that AO flood imaging provides reliable estimates of pericentral cone photoreceptor distribution in normal subjects.