Differences in pupillary light reflex between optic neuritis and ischemic optic neuropathy

Objectives To determine the differences in pupillary light reflex (PLR) between the acute and chronic phases of optic neuritis (ON) and nonarteritic anterior ischemic optic neuropathy (NAION). Methods The study included 30 patients with ON and 22 patients with NAION whose PLR were measured by a dynamic pupillometer (PLR-200; NeurOptics Inc., Irvine, USA). Age-matched controls included 58 healthy individuals with normal vision and optic nerve function. Pupil diameters, latency, constriction ratio, constriction velocity and dilation velocity were noted. The differences in PLR measurements were compared among the acute and chronic phases of ON and NAION, and in age-matched controls. Regression analysis determined factors associated with PLR measurements, including visual acuity, color vision defect, visual field defects and retinal nerve fiber layer thickness measurements on optical coherence tomography. Results Pupillary constriction velocity, constriction ratio and latency were all significantly decreased in the acute phase of ON and NAION. ON showed significantly delayed constriction latency compared to NAION (P = 0.047). Pupillary constriction velocity, constriction ratio and latency were recovered in the chronic phase of ON (P = 0.038, 0.018, and 0.045), however, these parameters were not recovered in NAION (P = 0.693, 0.173 and 0.994). Conclusions Pupillary constriction velocity, constriction ratio, and latency were significantly decreased in the acute phase of ON and NAION compared to normal controls. ON showed delayed constriction latency compared to NAION. Decreased PLR were recovered in the chronic phase of ON, but not in NAION.