Choroideremia: melanopsin‐mediated postillumination pupil relaxation is abnormally slow

Mar 9, 2017Acta ophthalmologica

Slow pupil relaxation after light in choroideremia linked to melanopsin function

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Abstract

The maximum pupil constriction in patients with choroideremia was severely weakened in red light but only mildly weakened in blue light (p < 0.05).

Baseline pupil diameters were similar in patients with choroideremia and healthy controls (p = 0.48).
Postillumination pupil dilation after red light was normal, while it was extremely prolonged after blue light.
Patients with choroideremia showed no abrupt change in the dilation curve following blue light, with early-phase dilation completely abolished (p < 0.01).
Rod-cone-driven pupil responses were decreased, indicating effects of outer retinal degeneration.
Near-normal pupil constriction in blue light suggests that the melanopsin system may function normally.

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PURPOSE: To investigate the rod-cone and melanopsin pupillary light response (PLR) pathways in choroideremia.

METHODS: Eight patients with choroideremia and 18 healthy age-matched controls underwent chromatic pupillometry by applying blue (463 nm) and red light (643 nm) at 100 lux intensity to the right eye while recording pupil diameters. Absolute baseline pupil size (mm), normalized maximal pupil constriction and the early and late postillumination pupillary dilation, from 0 to 10 seconds and 10 to 30 seconds after the end of illumination, respectively, were determined. Postillumination responses to blue light were considered to be primarily driven by melanopsin activation of the intrinsic photosensitive retinal ganglion cells.

RESULTS: Baseline pupil diameters were comparable in patients with choroideremia and control subjects (p = 0.48). The maximum pupil constriction in patients with choroideremia was severely weakened in red light but only mildly weakened in blue light (p < 0.05). Postillumination dilation of the pupil was normal after red illumination but extremely protracted after blue illumination. Also, in contrast to healthy subjects, no abrupt change in the dilation curve was seen in the patients after the end of blue illumination, the early-phase dilation being completely abolished (p < 0.01).

CONCLUSION: Rod-cone-driven pupil responses were decreased as expected in an outer retinal degeneration, and near-normal pupil constriction in blue light supports that the melanopsin system is normal. In contrast, the lack of brisk early-phase dilation after blue illumination in choroideremia is remarkable and may be interpreted to mean that the absence of photoreceptor inhibition promotes a tonic contraction of the pupil.

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Choroideremia: melanopsin‐mediated postillumination pupil relaxation is abnormally slow

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