Pupillary responses to short-wavelength light are preserved in aging

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.

Figure 1. Pupillary light responses in aging.

(a) Pupil diameter is shown in a representative young adult and in an older adult exposed to a 4-min light exposure sequence. Each trial consisted of 1 min of darkness, 2 min of monocular exposure to a gradually increasing blue light (469 nm) or red light (631 nm) stimulus, and 1 min of darkness after light offset. The timing of the ramp-up light stimulus is shown at the top of the plot. Dose-response curves for pupillary constriction are shown for young normal subjects (n = 60, aged 21–30 years) and older subjects without cataract (n = 54, aged 50–74 years) exposed to either (b) blue light or (c) red light. In each panel, the mean ± SEM is shown and asterisks indicate significant differences between age groups.

Figure 2. Pupillary light responses in patients with cataract.

Dose-response curves for pupillary constriction are shown for older subjects (≥50 years) without cataract (n = 54), with mild cataract (n = 107), and with severe cataract (n = 18) exposed to a gradually increasing (a) blue light (469 nm) or (b) red light (631 nm) stimulus. In each panel, the mean ± SEM is shown. Asterisks indicate significant differences between patients without cataract versus those with severe cataract, and hashes (#) indicate significant differences between patients with mild cataract versus those with severe cataract.