Eye pressure can vary by several points (measured in mmHg) during the day, and infact is higher at night / when lying down. Normally, eye pressure is also higher in the morning on awakening. Drinking a large volume of water or fluid quickly can lead to a significant rise in eye pressure, in some individuals. The "water drinking test" used to be a test for glaucoma patients, but it is unreliable in general and not used nowadays. Nevertheless, patients with glaucoma might be advised not to drink very large volumes of fluid (eg large volumes of beer!) in a short period as this might cause a significant rise in eye pressure. Alcohol infact is not known to be harmful to the optic nerve, except if consumed in very large quantities. An occasional glass of wine particularly may be beneficial. A substance found in wine, resveratrol, is being investigation for its potential beneficial effect in glaucoma.

Eye pressure is also varies seasonally, and is higher (very slightly) in the winter months.

Goldmann tonometer tip for measuring IOP