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Stewart Thompson, Gabrielle Bui, Pratibha Singh, Xiu-Ying Liu, Randy H Kardon, Edwin M Stone; Divergent effects of rapid and slow photoreceptor degenerations on the pupil light reflex of mice.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):573.
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© ARVO (1962-2015); The Authors (2016-present)
Pupillometry is increasingly being applied as a measure of retinal function in the clinic and in laboratory studies of inherited retinal disease. However, the pupil light reflex axis is complex and the effects of diverse disease mechanisms and pathologies on pupil function are poorly understood. The purpose of this study was to determine how two distinct disorders of the rod and cone photoreceptor cells affected the pupil response in mice.
We measured the pupillary light reflex in mice with early and (rd1) and slow (Rd2P90) degeneration of the rod and cone photoreceptor cells. At 90 days of age, Rd2 mice retain ~60% of rods and cones, but these cells lack an outer segment making them relatively insensitive to light. The effect of disease on the melanopsin and rod/cone generated components of the pupil response were assessed using 1-s red and blue, and 60-s blue stimuli at 0.01, 0.1, 1.0 and 10.0 μW.cm-2.
Responses were severely reduced in rd1, having low amplitude and no post-stimulus residual constriction even at the highest irradiance. Remarkably, in Rd2P90 mice, responses were only slightly reduced in compared to wild-type, with a deficit more apparent to red than blue light. Indeed, there was no apparent difference in post-stimulus residual constriction and steady state responses at higher irradiances.
In rd1 mice, deficits in pupil responses largely track deficits in rod/cone function: requiring 5-log units higher irradiance to elicit responses to brief stimuli. However, the limited reduction in sensitivity in Rd2P90 mice did not reflect the severity of the structural or functional deficit in the rod and cone photoreceptor cells. In our previous work, an unexpectedly high amplitude ERG b-wave (12% of wild-type) pointed to an outer-retinal signal gain mechanism. These pupillometry data suggest there may be additional signal gain mechanisms acting on the pupil light reflex axis in slow photoreceptor degeneration of Rd2P90 mice.
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