Pupil Diameter

The width of the opening in the iris through which light enters the eye, typically ranging from about 2mm in bright light to 8mm in darkness. Pupil diameter significantly affects visual quality because it determines how much of the eye's optical aberrations influence the image formed on the retina — larger pupils admit more peripheral light rays that are subject to greater aberration. This is particularly relevant to accessibility technologies like display pre-compensation, which must account for changes in pupil size to maintain effectiveness across different viewing conditions.