The eye pressure is fluctuating during a whole day. Usually, the top value will be appeared before you get up, and the lowest value is appeared in the afternoon. The eye pressure will be raised after the painstaking work, or labored breathing, or after the head bowing. If you want to lower your eye pressure, please drink a little water and take some exercise in a modest way. The eye pressure's fluctuating must be within the value of 5mmHg, or the eyes will suffer disease.
The term ocular hypertension usually refers to any situation in which the pressure inside the eye, called intraocular pressure, which also has a commonly name-eye pressure. High pressure inside the eye is caused by an imbalance in the production and drainage of fluid in the eye. What you said is true that eye pressure is different in a same day. Blood vessels can work normally in the morning because people are fresh and relaxation after a whole night sleeping. While at afternoon, our nerves begin to feel tired, even fatigue, and then this condition may increase too much pressure in blood vessels to promote blood circle normally. The blood vessels around eyes are as the same. So usually eye pressure is higher at afternoon than in the morning.