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Arkady Lyubarsky, Therese Cronin, Jean Bennett; Flash Pupillometry as a Tool for High Sensitivity Non-invasive Testing of the Retinal Function in Mice. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5644.
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To determine rod and cone pathway contributions to the pupil light reflex in mice, and evaluate utility of the pupillary reactions in mice for assessment of the retinal function.
C57Bl/6J, rod opsin null (Rho-/-), retinal degeneration 1 (rd1) and retinal degeneration 10 (rd10) dark-adapted overnight and their pupil reactions to 20-60 ms flashes were monitored with an A1000 pupillometer (Neuroptics, San Clemente, CA) equipped with custom made filter holders and optical filters.
In 4 week old rd1 mice, 20 ms achromatic flashes delivering up to 4.3 scot lux s (estimated to produce ~250 photoisomerizations (phi) per rod in the wild-type mouse) did not elicit any pupil responses. Thus, in this range of flash stimulus intensities, the melanopsin-associated non-imaging photoreceptive system is not responsive and pupil reactions are controlled by the rod-cone system. In the wild-type mice, pupil reflex threshold was ~10-4 phi/rod, which is close to the level of noise caused by spontaneous photoisomerizations of the rod visual pigment; and the intensity-response relation obeyed the Weber-Fechner law (12-15% change in the pupil diameter per log unit of stimulus intensity increase). In 4 week old Rho-/- mice, flashes delivering 1.5 scot lux s (under the threshold for the melanopsin system) elicited 10-20% transient pupil contraction mediated by a cone-driven pathway. As a case study demonstrating utility of flash pupillometry for assessment of the retinal function in genetically modified mice, we studied pupil reflexes in dark-raised rd10 mice. We have shown that pupil responses in these animals also obeyed the Weber-Fechner law but exhibited somewhat lower sensitivity, ~5% change/log unit of flash intensity.
(1) The melanopsin-associated pathway for pupil size control is at least 106 times less sensitive to flash stimuli compared to the rod-cone pathway; (2) Both rod and cone signaling cause pupil reactions; (3) Flash pupillometry is a sensitive tool for assessment of the retinal function in mice.
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