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Robert F Cooper, Christopher S Langlo, Drew H Scoles, Kimberly E Stepien, Thomas B Connor, Alfredo Dubra, Joseph Carroll; Assessing Photoreceptor Reflectance Changes in Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2617.
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© ARVO (1962-2015); The Authors (2016-present)
It is well established that photoreceptor reflectance fluctuates over time when imaged with adaptive optics (AO) techniques, though the origin of these changes remains unclear. In order to elucidate the origin of these reflectance variations, we examine this variability in cone photoreceptors in subjects with retinitis pigmentosa (RP) compared to normal subjects.
Four subjects with no known retinal pathology and 2 subjects with RP (1 simplex, 1 Usher Syndrome) were imaged using an AO scanning light ophthalmoscope (AOSLO). Image sequences of the parafoveal cone mosaic were obtained using a 790nm (12.1 μm coherence length) source every 5 minutes for 1 hour. Average images from each time point were aligned, and cell locations were determined. Temporal cone reflectance profiles were classified as flat, monotonic, oscillating or spiking, and compared using a chi-squared test for independence. Additionally, cone reflectance was compared using standard deviation and range over both time and spatially within each image. Images of cone inner segment structure were acquired using a split-detector AOSLO.
We analyzed 16,963 cones across all images. Cones in RP and normal subjects had significantly similar (p<0.0001) classifier distributions. The average standard deviation of spatial cone reflectance was greater in RP (32 and 31 AU) than in normal subjects (range: 18-26). The range of cone intensities was 193 and 214 AU in RP subjects, similar to normal subjects (range: 174-222). Temporal cone profiles had a standard deviation of 16 and 13 in RP and 12 AU on average in normal subjects (range: 10-14). Profiles had a range of 52 and 46 in RP subjects, and 40 AU on average in normal subjects (range: 35-48). Despite 159 cones in one RP subject lacking reflectivity in confocal AOSLO, intact inner segment structure was observed using split-detector AOSLO. Including these cells in the reflectance analysis resulted in an increase in spatial standard deviation (31.4 AU), and a decrease in temporal standard deviation (13.3 AU) and dynamic range (44 AU).
The reflectance behavior of cones in subjects with RP appears different than in subjects without retinal pathology, suggesting that reflectance may be a useful biomarker in retinal diseases that affect the outer segment. Split-detection AOSLO imaging showed that failure to include non-reflective cells can lead to substantial errors in temporal or structural analyses.
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