Ophthalmology in the Blink of an Eye: The Light-Induced Eyelid Reflex

Background: A video-based assessment of the light-induced eyelid reflex, termed the photic blink reflex (PBR), was quantified based on the degree of palpebral fissure (PF) narrowing as a noninvasive test of visual input. The physiology of PF narrowing in response to light intensity was compared to the pupil light reflex, measured simultaneously. Methods: Eyelid and pupil responses to flashes of white light stimulus, increasing in intensity, were video recorded in 53 subjects using a monocular hand-held device. Responses to photopic red and blue light stimuli were recorded in 5 subjects. Percent-change of PF width and pupil width from the prestimulus baseline was measured. Results: In 81% of subjects, there was significant correlation between PF narrowing and light stimulus intensity. There was no correlation between the PBR and the pupil light reflex in the same eye in normal subjects. There was no sustained postillumination PF narrowing to bright blue-light stimuli compared to the postillumination sustained pupil response that was present in response to the same stimulus. Conclusions: The photic blink reflex can be quantified with video recording of the palpebral fissure. The photic blink reflex has potential utility as an alternative to the pupil light reflex in assessing asymmetric pathologies of the afferent visual pathway, especially in eyes with pharmacologically dilated or unreactive pupils.