Pupillary responses to short-wavelength light are preserved in aging

A V Rukmini,Tin Aung,Dan Milea,Joshua J Gooley

doi:10.1038/srep43832

Abstract

With aging, less blue light reaches the retina due to gradual yellowing of the lens. This could result in reduced activation of blue light-sensitive melanopsin-containing retinal ganglion cells, which mediate non-visual light responses (e.g., the pupillary light reflex, melatonin suppression, and circadian resetting). Herein, we tested the hypothesis that older individuals show greater impairment of pupillary responses to blue light relative to red light. Dose-response curves for pupillary constriction to 469-nm blue light and 631-nm red light were compared between young normal adults aged 21–30 years (n = 60) and older adults aged ≥50 years (normal, n = 54; mild cataract, n = 107; severe cataract, n = 18). Irrespective of wavelength, pupillary responses were reduced in older individuals and further attenuated by severe, but not mild, cataract. The reduction in pupillary responses was comparable in response to blue light and red light, suggesting that lens yellowing did not selectively reduce melanopsin-dependent light responses. Compensatory mechanisms likely occur in aging that ensure relative constancy of pupillary responses to blue light despite changes in lens transmission.

Highlights

Aging is associated with yellowing of the lens and reduced transmission of short-wavelength light
This criterion ensured that pupillary constriction responses could be compared reliably between blue and red light stimuli in each participant
Despite the marked reduction in retinal exposure to blue light that occurs in aging, we found that pupillary responses in older individuals were not impaired by a greater amount during exposure to blue light relative to red light

Summary

Introduction

Aging is associated with yellowing of the lens and reduced transmission of short-wavelength light This arises from age-dependent accumulation of pigments in the crystalline lens that preferentially absorb blue light[1]. It is widely believed that attenuation of short-wavelength light by the aging lens can lead to diminished non-visual light responses (e.g., pupillary light responses, melatonin suppression, and circadian entrainment)[3]. It has been estimated that the amount of 480-nm light that can pass through the lens in late adulthood (80-year-old lens) is less than a third relative to childhood[6] This age-dependent reduction in short-wavelength light reaching the retina has been hypothesized to contribute to reduced circadian responses to light and sleep disturbances[3,7,8,9]. We hypothesized that aging and increased cataract severity would be associated with a greater reduction in sensitivity of the pupillary light reflex to blue light relative to red light, revealing a functional consequence of age-dependent yellowing of the lens for melanopsin-dependent photoreception

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