Why are glasses measurements important?

Pupillary distance

PD measurement is the distance between the center of your pupils. This measurement is important because it ensures your lenses are directly aligned over the center of your pupil to give you the best and clearest vision. We can take binocular PD which is the distance between the center of one pupil to the center of the other pupil. Or we can take monocular PD which is the distance between the center of each pupil to the nose bridge. This gives two numbers.

Ocular center

OC height is the measurement of the lens vertically. We take this from the bottom of the lens to the center of the pupil. This is important because this will help ensure you get the clearest vision directly in the center of your pupils.

Segment height

Seg height is the vertical measurement from the bottom of the lens to the beginning of the progressive addition or the top line of a lined bifocal.