Intraocular Pressure (IOP) is the internal pressure exerted by the fluid within the eye’s structure. Maintaining this specific pressure is fundamental to eye health and function. The eye relies on constant pressure to maintain its precise spherical shape, which is necessary for light to focus correctly onto the retina and enable clear vision. Monitoring and managing this pressure is a significant part of preventative eye care, as deviations from a healthy range can indicate underlying problems that threaten sight.
Understanding Intraocular Pressure
The pressure inside the eye is created and sustained by a clear fluid called the aqueous humor. This fluid is actively produced by the ciliary body, a structure located behind the iris, and flows into the front chamber of the eye. The aqueous humor serves a dual purpose: providing nutrients to the lens and cornea, and physically inflating the globe of the eye.
The level of pressure results from a constant balance between the rate of the fluid’s production and the rate of its drainage. Aqueous humor primarily exits the eye through the trabecular meshwork, a spongy tissue that acts like a filter near the junction of the iris and cornea. Interference with this outflow pathway, such as increased resistance within the meshwork, causes the fluid to accumulate, leading to an increase in intraocular pressure.
Defining the Healthy Range and Measurement
The widely accepted range for healthy intraocular pressure is generally between 10 and 21 millimeters of mercury (mmHg). An average IOP often falls around 15 to 16 mmHg, though this figure naturally fluctuates throughout the day and varies between individuals.
Measuring this pressure is accomplished through a painless procedure called tonometry, a standard part of a comprehensive eye exam. The most accurate method, considered the gold standard, is Goldmann applanation tonometry, where a small, flat-tipped probe gently touches the anesthetized cornea. This method calculates the IOP based on the force needed to flatten a specific area of the cornea.
A quicker, non-contact method, often called the “air puff” test, is frequently used for initial screening. This technique estimates the pressure by directing a puff of air onto the cornea and measuring the time it takes to flatten the surface. While the non-contact method is convenient and does not require numbing drops, its readings can be less precise than Goldmann tonometry, especially at higher pressure levels. A reading above 21 mmHg does not automatically mean a person has a disease, but it signals a need for further specialized evaluation.
The Risks of Elevated Eye Pressure
When intraocular pressure is consistently above the typical range, the condition is referred to as ocular hypertension. This elevated pressure is the primary risk factor for developing glaucoma, a condition that results in permanent damage to the optic nerve. The optic nerve transmits visual information from the retina to the brain.
Sustained high pressure physically stresses the delicate fibers of the optic nerve head where they exit the eye. This mechanical strain leads to progressive degeneration of the retinal ganglion cell axons, which form the optic nerve. The damage results in a painless, gradual loss of peripheral vision. Low eye pressure, or hypotony, is much rarer but can also be problematic, potentially leading to blurry vision or indicating issues from trauma or prior surgery.