Effects of varying light conditions and refractive error on pupil size

Abstract

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.

Keywords:

• visante optical coherence tomography
• refractive error
• pupil size
• illumination

Public Interest Statement

Vision is dependent on illumination. As light level increases, the pupil constricts in order to reduce the amount of light scatter and retinal illuminance, thereby increasing visual acuity. The aim of the present study is to investigate the effects of small scale illumination levels and refractive error type on the pupil size measured in healthy eyes. In refractive error, as the magnitude of spherical error increases, pupil size decreases. To examine the effect of light conditions in the presence of refractive error, subjects were grouped as myopes, and emmetropes. Pupil size measurements were performed with room lights at five different levels. Pupil size of each eye was measured three times and then mean calculated. This study examined that the pupil size decreases in linear manner with increasing illumination.

The pupil size data under various light levels obtained here may assist in understanding the pupillary light reflex and in diagnosing pupillary abnormalities.

Competing Interests

The author declare no competing interest.

Additional information

Notes on contributors

Farah Maqsood

Farah Maqsood is working as Assistant Professor at the Department of Optometry, College of Applied Medical Sciences, King Saud University, Saudi Arabia. She received a PhD degree in Physics from the Aligarh Muslim University, India. Her main fields of research areas include psychophysics, retinal imaging through the use of adaptive optics and light scattering techniques, fundamental visual processes, ophthalmic and physiological optics, novel applications of optics for visual science and role of different luminance in vision, Prismatic effect related.