Association Between Postillumination Pupil Response and Glaucoma Severity: A Cross-Sectional Analysis of the LIGHT Study.

Purpose: This study determines whether the functional and structural severity of glaucoma is associated with intrinsically photosensitive retinal ganglion cell (ipRGC) function. Methods: This cross-sectional study assessed 148 eyes from 148 patients with glaucoma (mean age 70.5 years). The ipRGC function was assessed by postillumination pupil response (PIPR) using the pupil diameter after exposure to blue and red light. Main outcome measures were as follows: six-second PIPR amplitude, net PIPR, and net PIPR change. Functional and structural glaucoma severities were evaluated using visual field mean deviation (MD) and the circumpapillary retinal nerve fiber layer (RNFL) thickness, respectively. Results: Multivariable analysis adjusting for age, sex, body mass index, hypertension, diabetes, oral medication use, cataract surgery, axial length, and topical alpha2-adrenergic receptor agonist use showed that worsening in visual field MD was significantly associated with higher blue six-second PIPR amplitude (regression coefficient per -1 dB worsening, 0.25; 95% confidence intervals [CI], 0.14, 0.37; P < 0.001). The thinner RNFL thickness was significantly associated with higher blue six-second PIPR amplitude, lower Net PIPR change, and lower net PIPR (blue six-second PIPR amplitude: regression coefficient per 10-µm thinning, 1.29; 95% CI, 0.72, 1.87; P < 0.001; net PIPR change: regression coefficient, -0.70; 95% CI, -1.26, -0.14; P = 0.015; net PIPR: regression coefficient, -0.03; 95% CI, -0.05, -0.001; P = 0.044). No significant association was found between glaucoma severity and red six-second PIPR amplitude. Conclusions: Our findings revealed a significant association between functional and structural glaucoma severity and impaired ipRGC function independent of potential confounders.