Ocular Phototherapy and Mental Health: What Vision Scientists and Clinicians Need to Know
Year: 2026
Type: preprint
Abstract: Bright light therapy is an effective and inexpensive non-pharmacological treatment for seasonal affective disorder (SAD) and, increasingly, for nonseasonal and bipolar depression. Its mechanism is a problem in vision science: light acts through the eye, chiefly through melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) working together with rods and cones. This narrative review, written for both vision scientists and clinicians, integrates research on ipRGC pathways to circadian, geniculate and mood-related brain regions; evidence from blind people with and without functioning ipRGCs; action spectra for melatonin suppression; trials comparing light spectra in SAD; ocular aging and safety; and clinical efficacy. Using published international standard tabulations, it also calculates melanopic dose, age-related loss and blue-light-hazard weighting for representative light sources. Narrow-band short-wavelength (blue-appearing) light outperforms dim long-wavelength (red-appearing) light in SAD but has not outperformed broadband white light, even though melatonin suppression peaks at 446–477 nm. Light rated at 10,000 photopic lux delivers between about 4,100 and 10,000 lux of melanopic equivalent daylight illuminance, depending on its spectrum. The aging ocular media roughly halve the retinal melanopic dose between ages 25 and 75, although older adults may partly compensate physiologically, and compensating with added short-wavelength light increases blue-light-hazard-weighted exposure in the population with the highest prevalence of retinal disease. The therapeutic dose of light is therefore a retinal quantity that depends on spectrum, geometry, pupil size and age. The review closes with recommendations for prescribing and reporting light therapy and with open questions for both disciplines.
Source: PsyArXiv (OSF Preprints)
Author: David Henry Peterzell
Language: English
Subfield: Endocrine and Autonomic Systems
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7223028990