Action spectrum for photophobia.

Thresholds for photophobia (light-induced discomfort) were determined at wavelengths from 440 to 640 nm for three subjects. Photophobia was assessed by means of electromyography, which was used to measure subjects' level of squinting. After correction for absorption by macular pigment and the ocular media, subjects' functions displayed a trend of increasing sensitivity with decreasing wavelength. We propose that the corrected function is indicative of increased sensitivity to potential retinal damage by short-wavelength light. It is therefore suggested that photophobia serves a function of biological protection. Results also suggest that photophobia is significantly mitigated by macular pigment in the short wavelengths.