Development and Implementation of a Handheld Pupillometer for Detection of Optic Neuropathies

Purpose: Quantitative pupillometry has utility in research settings for measuring optic nerve and autonomic function. We configured a portable device to perform quantitative pupillometry with application to detecting unilateral optic neuropathies in the clinical setting.Materials & methods: Light stimuli were delivered, and pupil diameter responses recorded using customized software implemented on a commercial portable electroretinography device. Increasing pupillary constriction occurred with increasing duration and intensity of full field blue light (470 nm) stimuli in healthy subjects. Flashes of 1 s dim (50 cd/m²) and bright (316 cd/m²) blue light were administered to both eyes of subjects with unilateral optic neuropathies (n = 10) and controls (n = 5). Maximum pupillary constriction (C_max) for each stimulus was compared between control eyes and optic neuropathy eyes. C_max for the inter-eye difference curve (C_diffmax) was compared between control and optic neuropathy subjects.Results: The pupil protocol lasted 15 minutes and was well tolerated by subjects. C_max for bright and dim stimuli was reduced in eyes with optic neuropathy compared to fellow and control eyes (p < .0005 for all). Inter-eye C_diffmax was larger in optic neuropathy subjects than control subjects for both dim and bright stimuli (p = .002, <0.0005). There was no overlap between groups for C_max and C_diffmax for either stimulus.Conclusions: A portable pupillometer was implemented on a commercial portable electroretinography platform and applied in a pilot manner to subjects with and without unilateral optic neuropathies. Optic neuropathy eyes were distinguished from non-optic neuropathy eyes both within and between subjects.