Eye pressure follows a circadian rhythm, peaking at night and in the early morning hours.

“it turns out that our eye pressure also under goes the Circadian rhythm and it's actually highest at night while we're sleeping kind of peaks in those early morning hours then hits a low throughout the early day and then kind of rises again throughout the afternoon into the evening and uh we have a lot of patients who they come into their Clinic visit their eye pressure looks normal but it's actually quite a bit higher when they're at home and that could explain some fraction of what we call normal pressure glaucoma it just looks normal during the day it's actually high at night”