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Nabin Joshi, Suresh Viswanathan, Cristina Llerena Law; Test-retest variability of pupil responses mediated by intrinsically photosensitive retinal ganglion cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4117.
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Recent studies indicate that sustained pupil responses elicited to intense blue stimuli are likely to be driven by intrinsically photosensitive retinal ganglion cells (ipRGC) and testing ipRGC responses in patients with outer retinal degeneration could be a viable strategy for assessing the function of inner retinal neurons in patients who are candidates for visual prostheses or gene therapy (Park et al., IOVS 2011). We determined the test-retest variability of the sustained pupil responses in a small cohort of normal subjects.
Pupil responses were measured from 10 normal healthy subjects (mean age 34.7 ± 7.18 years, 6 males and 4 females) on two occasions using an RAPDx pupillometer from Konan Medical Inc at a sampling rate of 32 ms. Baseline pupil diameter was measured over 300 ms following 10 minutes of dark-adaptation. Subsequently, pupil diameter was measured in response to a 20 phot cd/m^2 blue (RGB 0, 0, 255) test flash of 1 sec duration delivered on a LCD monitor. The diameters of the peak and sustained pupil constriction at 6 seconds following stimulus onset were analyzed after normalization to the baseline value. Test-retest reliability was assessed by Bland-Altman analysis.
The pupil diameters at baseline, peak and sustained constriction phases were 5.34+0.87 mm, 3.16+0.51 mm and 4.97+0.77 mm respectively with a coefficient of variation (CV) of approximately 16% for each phase. The diameters were significantly different for baseline vs peak (p<1.7x10^-7), baseline vs sustained (p<1.1x10^-7) and peak vs sustained (p<3.7x10^-7) phases. The diameters of the peak and sustained phases were 59.25+2.35% and 93.17+3.36% when normalized to baseline, with corresponding CVs of 3.9% and 3.6%. The mean test-retest difference of the normalized diameters was 1.68% and -4.58% respectively for the peak and sustained phases with corresponding 95% confidence intervals of 3.34% and 5.19% respectively which were not significantly different.
Sustained pupil constrictions to intense blue flashes can be elicited with a commercial system. The inter-subject and intra-subject variability of this measure is small and comparable when normalized to baseline values enabling the application of this technique to the investigation of patient populations with eye disease.
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