The role of retinal irradiance estimates in melanopsin-driven retinal responsivity: a reanalysis of the post-illumination pupil response in seasonal affective disorder

Jun 15, 2024Sleep

How light reaching the eye affects light-sensitive cells and pupil response in seasonal depression

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Abstract

The post-illumination pupil response (PIPR) was measured in 47 adults, including 25 with seasonal affective disorder (SAD), under controlled light stimuli.

PIPR measurements were taken over 50 seconds following 1 second of red and blue light exposure.
Statistical controls accounted for individual differences in non-melanopsin contributions, such as age and iris pigmentation.
The best-fitting models for PIPR included either estimated retinal irradiance or pupil light reflex (PLR), along with circadian timing.
PLR served as a contemporaneous measure reflecting nonspecific effects while being minimally burdensome for participants.
The study suggests that incorporating PLR could enhance methodological controls in future research on retinal sensitivity.

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To isolate melanopsin contributions to retinal sensitivity measured by the post-illumination pupil response (PIPR), controlling for individual differences in non-melanopsin contributions including retinal irradiance is required. When methodologies to negate such differences present barriers, statistical controls have included age, baseline diameter, iris pigmentation, and circadian time of testing. Alternatively, the pupil light reflex (PLR) and calculations estimating retinal irradiance both reflect retinal irradiance, while the PLR also reflects downstream pathways. We reanalyzed data from an observational, correlational study comparing the PIPR across seasons in seasonal affective disorder (SAD) and controls. The PIPR was measured in 47 adults in Pittsburgh, Pennsylvania (25 SAD) over 50 seconds after 1 second of red and blue stimuli of 15.3 log photons/cm2/s. The PLR was within 1 second while PIPR was averaged over 10-40 seconds post-stimulus. Two raters ranked iris pigmentation using a published scale. We evaluated model fit using Akaike's Information Criterion (AIC) across different covariate sets. The best-fitting models included either estimated retinal irradiance or PLR, and circadian time of testing. The PLR is collected contemporaneously in PIPR studies and is an individually specific measure of nonspecific effects, while being minimally burdensome. This work extends the prior publication by introducing theoretically grounded covariates that improved analytic model fits based on AIC specific to the present methods and sample. Such quantitative methods could be helpful in studies which must balance participant and researcher burden against tighter methodological controls of individual differences in retinal irradiance.

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The role of retinal irradiance estimates in melanopsin-driven retinal responsivity: a reanalysis of the post-illumination pupil response in seasonal affective disorder

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