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Adam Elias Brondsted, Birgit A Sander, Henrik Lund-Andersen; Seasonal variation in the response of intrinsically photosensitive retinal ganglion cells. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5571.
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© ARVO (1962-2015); The Authors (2016-present)
Intrinsically photosensitive retinal ganglion cells (ipRGCs) are responsible for photoentrainment of the circadian rhythm and form the afferent limb in the pupil light response. The ipRGCs are sensitive to blue light and exhibit circadian variation in the response to blue light. Seasonal rhythms in mammals are controlled by the circadian rhythm and hence, seasonal variation in the light response of the ipRGCs may exist. The purpose of this study was to investigate the effect of seasonal change on the ipRGCs measured by blue light pupillometry. As the ipRCG’s are known to respond with latency and a sustained activity, we quantified the post illumination pupil response (PIPR) as a surrogate marker of ipRCG stimulation.
Twenty five healthy participants with a mean age of 44 years (range, 23 - 69) were recruited for the study and examined at baseline (summer) and at 3 control visits until next summer. Consensual normalized pupil responses to bright blue light (470 nm, 300cd/m2) were recorded and the mean pupil constriction was calculated from 10-30 s after stimulus offset. Maximal and sustained pupil contraction was also calculated. Control recordings of red light (660 nm, 300cd/m2) elicited pupil responses were also obtained.
The mean blue light PIPR was 0.17 (0.14 - 0.21, 95% CI) at baseline and decreased significantly with 26% (-47 - -6%, 95% CI, P=0.01) at 188 days (winter) and returned to baseline values 1 year after (P=0.16). Maximal and sustained pupil constriction to blue light was unaffected and as were pupil responses to red light.
We found a seasonal variation in the blue light PIPR associated with the intrinsic response of the ipRGCs analogous to previous determined circadian variation. The response decreased during winter where ambient light intensities are lower at our latitude (in Denmark). These preliminary findings suggest that seasonal variation should be considered when following subjects over different seasons and indicate a novel adaptive mechanism in the intrinsic ipRGC response.
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