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Jason C. Park, J. Jason McAnany; Spatial summation characteristics of the pupillary light reflex differ under rod-, cone- and melanopsin-mediated conditions. Journal of Vision 2013;13(15):P3. doi: 10.1167/13.15.38.
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© ARVO (1962-2015); The Authors (2016-present)
This study examined whether spatial summation characteristics of the human pupillary light reflex (PLR) differ under rod-, cone-, and melanopsin-mediated conditions. Pupil size was recorded from four visually-normal individuals using an infrared camera. PLRs were elicited using a previously reported paradigm that consists of three conditions: 1) a −3 log cd/m2 short-wavelength (467nm) flash (rod condition); 2) a 2.6 log cd/m2 short-wavelength flash (melanopsin condition); 3) a 2.6 log cd/m2 long-wavelength (640nm) flash presented on a rod-desensitizing adapting field (cone condition). The rod and melanopsin responses were obtained after 10 minutes of dark-adaptation and the cone response was obtained after 2 minutes of light-adaptation to the rod- desensitizing field. The stimuli were 1 second in duration, presented in the central visual field, and had diameters of 4, 8, 16, 32 deg, or were full-field. The rod PLR showed broad spatial summation, increasing monotonically with stimulus size. The melanopsin PLR also showed spatial summation, but stimuli of at least 15 deg were necessary to evoke a clear sustained response. In contrast to the rod and melanopsin PLRs, spatial summation for the cone PLR was minimal; the PLR increased from 4 to 8 deg, and was independent of size for larger stimuli. The spatial summation characteristics of the rod and cone PLRs may be related to the density distribution of these photoreceptor types across the retina, or to the relative state of adaptation. These results may be useful for interpreting the PLR obtained under rod-, cone-, and melanopsin-mediated conditions in patients with visual field defects.
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