The inside of the eye has two separate chambers. The back chamber contains a jelly-like substance called vitreous. The vitreous does not drain out or replenish, but it ages along with the eye. The front chamber contains fluid called aqueous. The eyes continuously make this fluid, draining away the excess. If the fluid builds up in this front chamber, the intraocular eye pressure will increase.
Fluid Imbalance
One cause of increased intraocular pressure results from an imbalance in the fluid coming in and the fluid leaving the eye. The eye makes aqueous fluid at a relatively constant level. If the fluid drains too slowly, the pressure in the eye will increase, explains the National Eye Institute. This process is much like the gutters on a home. The gutters drain away excess rain water, but if the gutters do not drain fast enough, the water will build up. Eventually the rain water will spill over the side. The eye, however, cannot release the excess fluid, so the intraocular pressure increases.
Structural Abnormalities
The drainage channel for the aqueous fluid may have a blockage, and this will cause the eye pressure to increase. In some cases, the iris--the colored part of the eye--may completely or partially cover the drainage location, causing an increase in eye pressure, says the Glaucoma Research Foundation. This may result from abnormalities in the iris muscle or from changes in its ability to function. Additionally, people may have narrow drainage canals at birth. Other eye conditions may contribute to closing the angle, such as a dense cataract that pushes the iris against the drain, causing a blockage. Sudden pressure increases may cause intense pain, nausea and vomiting, and this requires immediate medical attention to prevent damage to the eye and permanent loss of vision.
Complications
People with an increased intraocular pressure usually do not have damage to the eye. However, in some people, the pressure may damage the optic nerve, a sensitive set of nerve fibers that relay visual information to the brain. If damage occurs, the person will suffer slow but permanent damage to vision. Side vision will diminish until a person feels as if she has tunnel vision, and this will ultimately lead to complete loss of vision, according to MayoClinic.com. This condition, called glaucoma, typically takes years to acquire. In such cases, proper treatment for high pressures may reduce the chance of vision loss.
