Features of Cone Photoreceptors on Adaptive Optics Retinal Imaging

Abstract

Purpose: To establish cone photoreceptor features acquired on an Adaptive Optics (AO) retinal camera and to correlate them to well-established parameters in retinal histology literature.

Methods: High-resolution AO retinal imaging, was performed on a group of ten healthy subjects, age 20-35 years old with an infrared flood-illumination AO camera (rtx1, Imagine Eyes, Orsay, France). Images were from the left eye 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 photoreceptors were counted using an automated algorithm and the density calculated. In the 3 subjects, manual photoreceptor count was also performed at 2, 3, 5 and 7 degrees and photoreceptor-packing was assessed by spatial frequency technique.

Results: The cone density at 5 degrees using the automated algorithm is 16.1 ± 1.3 x 10³ cones/mm² (mean ± SD), which is consistent with accepted histology. Cone density decreased with increasing retinal eccentricity from 2 to 7 degrees. Hexagonal pattern of photoreceptor packing was seen at 2, 3 and 5 degrees.

Conclusions: Imaging data acquired from the rtx1 AO camera shows the features of cone photoreceptors; decreasing density with increasing retinal eccentricity, hexagonal packing arrangement and the density at 5 degrees, all correlate closely with the retinal histology literature. This provides proof that cone photoreceptors are being imaged and these parameters define cone photoreceptors in adaptive optics retinal images. This imaging modality has the potential for assessing retinal diseases and outcomes of new cellular therapies in vivo.

Keywords: 648 photoreceptors • 550 imaging/image analysis: clinical • 688 retina