What does the term pupillary distance refer to?

Pupillary distance refers specifically to the distance between the centers of the pupils in each eye. This measurement is crucial for the proper fitting of glasses and contact lenses, as it ensures that the optical centers of the lenses align with the wearer's eyes. This alignment is essential for optimal visual acuity and comfort. Accurate pupillary distance measurement helps in avoiding eyestrain and ensures that the prescription is effective.

The other choices do not accurately define pupillary distance. The distance between the pupil and the lens is not a standard measurement used in optics. The distance from the cornea to the retina describes the anatomical depth of the eye but does not pertain to the measurement relevant for lenses. Lastly, the distance from the eyelid to the iris does not relate to pupillary distance and is not relevant in the context of fitting eyewear.