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Cord R H Huchzermeyer, Julia Auer, Jan J Kremers; Temporal contrast sensitivities elicited by the four photoreceptor classes using the silent substitution paradigm in retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):449.
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© ARVO (1962-2015); The Authors (2016-present)
To measure psychophysical temporal contrast sensitivities (TCS) elicited by the four photoreceptor classes (L-, M-, S-cones and rods) in the pericentral retina of patients with retinitis pigmentosa (RP) using the silent substitution paradigm.
Eleven patients with RP (3 AD, 1 AR, 1 X-linked, 2 Usher, 4 sporadic) were examined. Their data were compared with those from 18 normal subjects for the cone sensitivities and from 7 subjects for the rod sensitivities.<br /> Stimuli were created using an 8-channel LED stimulator with a 2° diameter central circular field and a 13° outer diameter annular surround field (each with 4 independent primaries). Sine-wave modulated stimuli were presented in the white surround field (mean luminance 2.7 log phot Td) while subjects fixated the darker steady central field.<br /> For each photoreceptor class, isolating stimuli were created using the silent substitution paradigm based on the 10° cone fundamentals and the scotopic luminosity curve. For each condition, the critical flicker fusion frequency (CFF) was determined at the maximal available contrast. TCS was measured at 1, 2, 4, 6, 8, 10, 12, 16, 20, and 28 Hz, but only up to the frequency just above the CFF. Thresholds were determined using a randomly-interleaved double staircase algorithm. Sensitivity was defined as 1/(contrast at threshold).
Measurements were feasible in 10 patients. One patient with X-chromosomal RP also displayed a deuteranomalous defect, so that data from this patient were excluded from further analysis.<br /> On average, sensitivities of the RP patients were lower at all frequencies and for all photoreceptor classes. Differences between patients and normal subjects were statistically significant at high frequencies for L-cones, M-cones and rods and at all frequencies for S-cones. Sensitivities showed significant overlap for L-cones and M-cones. In our population, the best diagnostic criteria were the rod sensitivities at 10Hz and at 12Hz (area under the ROC curve of 1).
Psychophysical measurements of TCS elicited by the different photoreceptor classes is feasible in patients with RP using our protocol. As expected, rod sensitivities were best suited to separate RP patients from normal subjects. In the future, our paradigm may allow more accurate genotype-phenotype correlations and offer advantages in the monitoring of RP progression.
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