The influence of ametropia on pupil diameter

The pupil changes its size in response to a series of factors among which the most relevant one is variations in the level of environmental brightness. Some studies proposed that pupil diameter can also be affected by refractive condition although no consensus has been reached on this topic as other intervening factors could also explain such trend.Here we used a causal approach to tackle this point. We measured pupil diameters in a group of myopes and a group of hyperopes in two separate conditions. A condition where participants did not wear any correction (NC condition) and a condition in which their ametropia was corrected by means of daily disposable contact lenses matching their individual spherical equivalent (CL condition). In both conditions, pupil diameter was assessed at three distinct light levels (photopic, mesopic and scotopic). Results revealed a significant difference in pupil diameter between hyperopes and myopes in the NC condition at all the three light levels. Nevertheless, this difference was robustly reduced in the CL condition suggesting a causal relationship between ametropia and pupil size.