Most types of glaucoma are caused by elevated intraocular pressures, which are the pressures within your eyes. Your intraocular pressures are determined by a balance between the production of the fluid within the eye and the outflow of the fluid from the eye. The fluid, called aqueous humor, is produced by the structure named the ciliary processes. These ciliary processes produce fluid at a constant rate. The fluid nourishes the eye by providing oxygen and glucose to maintain the health of the structures within the eye, such as the lens and the cornea. The aqueous humor passes from the posterior chamber of the eye, though the pupil, and into the anterior chamber of the eye.
The fluid drains from the anterior chamber through two outflow channels and eventually ends up in the bloodstream. The main outflow channel is called the trabecular meshwork or conventional pathway, and it circles the eye. The second channel is called the nonconventional pathway. Intraocular pressure elevation is almost always a result of problems in the outflow of aqueous humor from the eye, such as blockages, and very rarely due to problems in the outflow system itself. All the medications used to treat glaucoma either reduce the production of aqueous humor or increase the drainage or outflow capacity. Although it is theoretically possible for the intraocular pressure to be elevated because of increased production of aqueous humor, it in fact never occurs.
What is "normal" intraocular pressure?
As you would expect, "normal" varies from person to person. Normal eye pressures can fall within a range of 16 to 21 millimeters of mercury, with most people having normal eye pressure at 21 millimeters. However, eye pressure can fluctuate from hour to hour, day to day, and month to month.
Risk factors for glaucoma
- being over 55 years of age
- having a family history of glaucoma
- being very nearsighted
- having diabetes
- being African American