The balance between how much fluid is made, and how much leaves the eye, determines the pressure within the eye. All eyes have measurable pressure. However, when the amount of aqueous humor draining from the eye is reduced, the pressure within the eye can increase. This high pressure often leads to glaucoma. Although many people think of glaucoma as just one single disease, in fact there are many different forms of glaucoma.
Differences depend upon where in the eye the blockage to the drainage occurs.
Both the border between the iris and lens as well as the trabecular meshwork are areas where the flow of aqueous can be limited, leading to increased eye pressure. One type of glaucoma, papillary-block glaucoma, occurs with the former. It is called papillary-block glaucoma because the fluid is trapped behind the pupil. Sometimes a patient is unaware of the papillary-block. However, the eye may become red.