Effects of varying light conditions and refractive error on pupil size

Purpose: To investigate the effects of small scale illumination levels and refractive error type on the pupil size measured with Visante Optical Coherence Tomography in healthy eyes. Findings: Pupil size increased with illumination decrements. Mean pupil size was 3.5 mm at 550 lux, 4.2 mm at 350 lux, 5.2 mm at 150 lux, 5.03 mm at 40 lux, and 5.4 mm at 2 lux. In multi-pairwise comparison of the five illumination levels, there were significant differences (p < 0.05) down to 150 lux. Comparisons among 150, 40 and 2 lux show no differences (p > 0.05). Refractive error ranged from spherical equivalent of +0.50 to –7.75D. Group of myopes had larger mean pupil size than emmetropes at all light levels but was not significant (p < 0.05). Both refractive groups had some amount of increase in pupil size with illumination decrements. There were no hyperopes and presbyopes in the study. This study has demonstrated that ambient illumination levels from high to low cause increase in pupil size and refractive error does not appear to have an extra influence. At or below 150 lux, pupil was maximally dilated at about 5.2 mm. These findings may assist in further understanding pupillary light reflex. Subjects: Physical Sciences; Health and Social Care; Medicine, Dentistry, Nursing & Allied Health