Intraocular pressure (IOP), or eye pressure, refers to the fluid pressure inside the eye. Maintaining a healthy range is important for eye health. Elevated eye pressure often has no noticeable symptoms, making professional eye examinations crucial for detection.
Understanding Eye Pressure
Aqueous humor, a clear fluid, is continuously produced by the ciliary body behind the iris. It fills the front of the eye, nourishing the lens and cornea. The fluid then flows through the pupil into the anterior chamber, the space between the iris and cornea.
Stable eye pressure requires a balance between aqueous humor production and drainage. The primary drainage pathway is the trabecular meshwork, located where the iris and cornea meet. From there, the fluid flows into Schlemm’s canal and re-enters the bloodstream. This balance keeps eye pressure within a normal range, typically 10-21 mmHg.
Common Causes
High eye pressure (ocular hypertension) usually occurs when the eye’s drainage system, especially the trabecular meshwork, is inefficient. This impaired drainage causes aqueous humor to build up, increasing internal pressure. Less commonly, overproduction of aqueous humor can also elevate pressure.
Certain medications, especially corticosteroids, can increase eye pressure. This can happen with eye drops, oral intake, or injections, with topical applications often causing a greater rise. Eye injuries can also damage the drainage system, causing immediate or delayed pressure increases due to inflammation, bleeding, or scarring.
Underlying medical conditions also influence eye pressure. Diabetes and high blood pressure are linked to increased IOP risk. Genetics also play a role, as eye pressure is heritable, and specific genes influence IOP levels. Other factors like age (risk increases over 55) and certain ethnic heritages (Black, Asian, Hispanic) are associated with a higher likelihood of high eye pressure.
The Link to Glaucoma
High eye pressure is the primary risk factor for glaucoma, conditions that damage the optic nerve. The optic nerve transmits visual information to the brain; damage can lead to permanent vision loss. While elevated IOP increases risk, not everyone with high eye pressure develops glaucoma. Some tolerate higher pressures without damage, while others develop glaucoma even with normal pressure (normal-tension glaucoma).
Sustained high pressure can damage optic nerve fibers. Damage typically begins with gradual peripheral vision loss, often unnoticed until later stages. Primary open-angle glaucoma, the most common type, involves slow clogging of drainage canals, leading to gradual pressure increase and optic nerve damage. Angle-closure glaucoma involves sudden or gradual blockage of the drainage angle, causing a rapid, sometimes painful, pressure spike.
Detecting High Eye Pressure
Detecting high eye pressure involves a routine eye examination, including intraocular pressure measurement. This is done using tonometry. Goldmann applanation tonometry, a common method, involves numbing the eye and gently touching the cornea with a probe to measure the force needed to flatten a tiny area. This is considered a reliable measurement.
Non-contact tonometry, or the “air-puff test,” is another widely used method. It uses a rapid air puff at the cornea to estimate pressure without direct contact. Rebound tonometry is another technique where a small probe gently bounces off the cornea, often without numbing drops. Since high eye pressure often has no noticeable symptoms, regular eye examinations are important for early detection, especially for those with risk factors.