Purchase this article with an account.
Elaine M Wells-Gray, Susanna C Finn, Cherry Greiner, Stacey S Choi, Nathan Doble; Characterization of Human Photoreceptor Packing Arrangement as a Function of Retinal Eccentricity using an Adaptive Optics Scanning Laser Ophthalmoscope (AO-SLO). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):87.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The human photoreceptor mosaic has been well characterized through histological measurements from excised retina. In vivo measurements of cone photoreceptor packing have been reported by several research groups out to retinal eccentricities of 15°. Reports of rod properties in vivo are not so common. The aim of this study was to examine the packing arrangement of cone and rod photoreceptors in vivo at greater eccentricities than have currently been reported.
An adaptive optics scanning laser ophthalmoscope (AO-SLO) was used to image two human control subjects at the foveal center and 4 temporal retinal (TR) eccentricities extending out to 25°. Both subjects had low refractive error without any history of retinal disease and were imaged over a dilated pupil diameter of 7.2 mm. The AO system employed a Shack-Hartmann wavefront sensor and a 97 actuator deformable mirror to measure and correct for the ocular aberrations. The imaging wavelength was 680 nm with a field of view of 0.9° x 1° on the retina. The frame acquisition rate was 30 Hz and the confocal pinhole diameter was set to 1 Airy disk. In the subsequent post-processing, individual frames underwent strip-wise registration to remove eye motion and were then averaged to increase the signal-to-noise ratio. At each retinal location, the cone and rod spacing were measured.
The cone mosaic was clearly imaged at the fovea, 4, 8, and 13° TR in both subjects, and at 25° TR in subject 2. Mean cone spacing was 3.43 ± 0.44 µm, 9.01 ± 0.62 µm, 14.1 ± 1.86 µm, 18.1 ± 0.50 µm, and 19.7 µm, for fovea, 4°, 8°, 13°, and 25° TR respectively. The spacing increased sharply when moving out from the fovea, but then tapered beyond 8° TR. Rod photoreceptors were clearly visible at 4, 8, and 13° TR in both subjects, with mean spacing of 3.18 ± 0.03 µm, 3.31 ± 0.25 µm, and 3.82 ± 0.06 µm respectively. The visibility of the rod mosaic especially at the higher eccentricities was found to be highly sensitive to the plane of focus.
Results for both cone and rod photoreceptor spacing as a function of retinal eccentricity show good agreement with known distributions established by histology. This data can serve as a benchmark against which diseased retinas (e.g., age-related macular degeneration and retinitis pigmentosa) can be compared.
This PDF is available to Subscribers Only