Discomfort from glare: The role of pupillary hippus

An infra-red pupillometer was used to record pupillary unrest, or hippus, on three observers at various steady illuminance levels. Frequency spectrum analysis of pupillary oscillations shows that, in logarithmic units, amplitude per unit frequency is a decreasing linear function of frequency, and that amplitudes are reduced at higher illuminance levels. Hippus was then recorded for one observer in the presence of extreme discomfort glare. The resulting frequency spectrum is very similar to spectra obtained in high luminance non-glaring conditions. It is concluded that pupillary hippus is unlikely to be a factor in the genesis of the discomfort felt under conditions of glare.