The photic blink reflex as an index of photophobia

• Published in: Biological psychology 2023-11, Vol.184, p.108695-108695, Article 108695
• Main Authors: Hackley, Steven A., Johnson, Lenworth N.
• Format: Article
• Language: English
• Subjects: Intrinsically photosensitive retinal ganglion cells (ipRGCs); Migraine headache; Photic blink reflex; Photophobia; Pupillary light reflex
• ISSN: 0301-0511; 1873-6246
• DOI: 10.1016/j.biopsycho.2023.108695

Two recent studies of eye closure triggered by intense luminance increase suggest that this behavior reflects the melanopsin-based retinal activity known to underlie photophobia, the pathological aversion to light (Kardon, 2012; Kaiser et al., 2021). Early studies of the photic blink reflex (PBR) are reviewed to help guide future research on this possible objective index of photophobia. Electromyographic recordings of the lid-closure muscle, orbicularis oculi, reveal distinct bursts with typical onset latencies of 50 and 80 ms, R50 and R80, respectively. The latter component appears to be especially sensitive to visual signals from intrinsically photosensitive retinal ganglion cells (ipRGCs) and to prior trigeminal nociceptive stimuli. The authors argue that the R80’s function, in addition to protecting the eyeballs from physical contact, is to shape the upper and lower eyelids into a narrow slit to restrict incoming light. This serves to prevent retinal bleaching or injury, while allowing continued visual function. •Recent findings indicate that reflexive blinking or squinting to bright light is increased in patients with migraines.•Early research documented an interaction of visual and nociceptive stimulation on reflexive lid closure.•The authors propose that the late, sustained component of the photic blink is driven primarily by melanopsin afference.•This component shapes the eyelids into a squint, which helps block painfully bright light.