Factors influencing the pupillary light reflex in healthy individuals.

Purpose: To determine the ocular anatomical factors influencing the pupillary light reactions to different wavelengths of light, measured with chromatic pupillometry.

Methods: Community-based, cross-sectional study including subjects with normal ocular health (ages 50-79 years). Direct pupillary responses to continuously increasing irradiances (6.8 to 13.8 log photons cm(-2) s(-1)) of red (631 nm) and blue (469 nm) light were measured, using a dedicated infrared pupillometer. All subjects underwent swept source optical coherence tomography (SS-OCT, CASIA SS-1000, Tomey Corporation, Nagoya, Japan) and noncontact partial coherence laser interferometry (Lenstar LS900, Haag-Streit AG, Switzerland). Univariate and multivariable regression analyses were performed to determine the anatomical features influencing pupillographic parameters.

Results: Among the 177 included subjects, 167 (94.4 %) were Chinese and 116 (65.5 %) female. The average baseline pupil diameter in darkness (β = -0.080, p < 0.001) and the amplitude of the relative pupillary constriction (β = -0.233, p = 0.006) to blue light decreased with age. The amplitude of pupillary constriction was significantly larger in patients with a thinner iris, in response to stimulation with blue (β = -0.321, p < 0.001) and red light (β = -0.336, p < 0.001). Other ocular parameters (i.e., lens vault, anterior chamber depth width, iris volume, iris curvature, and lens thickness) were not significantly associated with pupillometric outcomes.

Conclusions: The amplitude of the pupillary light constriction to chromatic photic stimuli is reduced with increasing age and iris thickness in subjects with normal ocular health, a finding which needs to be integrated into future pupillometric studies.