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Adam Boretsky, Faraz Khan, Erik van Kuijk, Massoud Motamedi; Adaptive Optics SLO Imaging of Macular Photoreceptors: Variations in Automated Cone Density Measurements Based on Confocal Pinhole Diameter. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3196.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the repeatability and variance in automated measurements of human macular photoreceptor packing density in vivo as a function of confocal pinhole diameter using a custom adaptive optics scanning laser ophthalmoscope (AOSLO).
An investigational AOSLO was used to acquire images of the photoreceptor mosaic with retinal eccentricity along the superior, inferior, nasal and temporal meridians. The SLO light source used was a superluminescent diode (SLD) centered at 830 nm with a bandwidth of 62 nm. The principle Adaptive optics (AO) components are the Hartmann-Shack wavefront sensor and a large stroke deformable mirror (Mirao 52d, Imagine Eyes). A series of 2º x 2º (1024 x 1024 pixel resolution) images were manually stitched together to create the final retinal montage. Individual imaging frames were analyzed for the photoreceptor density measurements. Three pinhole diameters (100, 200, & 400 µm) were selected to test the repeatability and variance of an automated image processing algorithm. This technique was used to identify individual photoreceptors and calculate the corresponding packing density throughout the macula.
The repeatability of the macular photoreceptor density analysis exhibited consistent results when compared to other published methods of determining cone packing density in vivo. In most cases, the repeatability of the photoreceptor counts yielded a standard deviation of less than 1000 cones/mm2 when analyzing multiple images from the same retinal eccentricity of 2° from the center of the fovea. The diameter of the confocal pinhole appears to influence the automated photoreceptor density assessment. In each case, image analysis of the average cone packing density resulted in the identification of an increasing number of cones as a function of decreasing pinhole diameter.
We have shown that an automated assessment of photoreceptor density can yield highly reproducible results throughout the macula which may be helpful as a diagnostic tool for monitoring the progression of retinal diseases. However, photoreceptor density measurements may be influenced by the diameter of the confocal pinhole. Calibration of this particular parameter must be considered when conducting time-course studies to quantify changes in the photoreceptor population.
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