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A. E. Elsner, T. Y. Chui, B. P. Haggerty, D. A. VanNasdale, S. A. Burns; Counting Cones in Eyes With Subtle Defects in the Retinal Pigment Epithelium by Autofluorescence or Scattered Light Imaging. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2330. doi: https://doi.org/.
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To determine for middle-aged subjects the structural integrity and distribution of cones that overlie subtle, changes to the retinal pigment epithelium. To assess the guiding of light by cones in region of patchy autofluorescence, retinal pigment epithelial (RPE) defects, or small drusen. The fundus changes were documented with long wavelength autofluorescence and scattered light image using scanning laser polarimetry.
Four subjects, 2 females and 2 males ages 52 - 59 yr who had not had previous cone count measurements, were recruited based on fundus status. The RPE was assessed using widefield autofluorescence measurements performed with an SLO, using 594 nm at 92 microwatts over a 27 x 23 deg field, with 750 x 456 pixels. The RPE was further assessed by computing the depolarized light image, using confocal scanning laser polarimetry using 780 nm at 2-3 milliwatts over a 15 x 15 deg field with 256 x 156 pixels. Regions of interest had subtle or small aging changes, including patchy autofluorescence, RPE defects. Control areas at similar eccentricities were selected. Cones were assessed using a second generation Adaptive Optics Scanning Laser Ophthalmoscope at 840 nm +/- 6 nm at 185 microwatts covering 530 x 550 microns of the retina. Cones were measured outside the central fovea where the density with eccentricity varies gradually, allowing better comparison to control regions.
Clear-cut guiding of light by cones, allowing cone counting, was clearly visible in all eyes, with two subjects tested without mydriatics. There were individual differences in the distribution of cones, and also the strength of light return from cones, both among subjects and within an eye. The regions of RPE defects had entire patches of either missing or poorly guiding cones, with control patches having densely packed, more uniformly distributed cones. In the subjects with visible RPE defects, the ratio of average cone densities was 1.14 and 1.02 for control:abnormal, but more important the distribution of the cones was nonuniform in affected regions. In one region of about 90 x 100 microns, there were few cones visible. The lateral resolution of the AOSLO, also demonstrated smaller patchy changes near the target regions, not amenable to imaging with wide field techniques.
Older normal subjects have subtle RPE changes that are visible with advanced imaging techniques. The distribution of cones that guide light in these subjects is nonuniform, and at least some of the regions lacking cones overlie defects in the RPE detectable by depolarization or fundus autofluorescence.
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