Factors affecting light-adapted pupil size in normal human subjects

To investigate the effect of age, gender, refractive error, and iris color on light-adapted pupil size in humans. Pupil diameters of 91 subjects (age range, 17 to 83 years) with normal, healthy eyes were measured using an objective infrared-based continuous recording technique. Five photopic ocular illuminance levels were used (2.15 to 1050 lumens m-2), and the accommodative status of each subject was precisely controlled at a constant level. Pupil size decreased linearly as a function of age at all illuminance levels. Even at the highest illuminance level, there was still a significant effect of age upon pupil size. The rate of change of pupil diameter with age decreased from 0.043 mm per year at the lowest illuminance level to 0.015 mm per year at the highest. In addition, the variability between pupil sizes of subjects of the same age decreased by a factor of approximately two as luminance was increased over the range investigated. Pupil size was found to be independent of gender, refractive error, or iris color (P > 0.1). Of the factors investigated, only chronologic age had a significant effect on the size of the pupil. The phenomenon of senile miosis is present over a wide range of ocular illuminance levels.