Factors influencing the pupillary light reflex in healthy individuals

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

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.

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.

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.