Intraocular pressure (IOP), also known as eye pressure, refers to the fluid pressure inside the eye. This pressure is created by a clear fluid called aqueous humor, which constantly flows in and out of the eye. Maintaining a balanced flow of this fluid helps the eye keep its shape and supports its internal structures.
Understanding the Normal Range
The generally accepted normal range for eye pressure falls between 10 and 21 millimeters of mercury (mmHg). The “mmHg” unit indicates millimeters of mercury, a standard scale for measuring pressure. This range represents the force exerted by the aqueous humor against the inner walls of the eye.
While 10-21 mmHg is a common guideline, normal pressure can vary for each individual. About 90% of people have eye pressure within the 10 to 20 mmHg range. Factors such as age, corneal thickness, and time of day can influence a person’s eye pressure.
Eye pressure can fluctuate throughout the day, known as diurnal variation. For instance, the highest eye pressure often occurs in the early morning, with approximately 65% of peaks happening before noon. These daily variations mean that a single pressure reading might not fully represent a person’s typical eye pressure.
How Eye Pressure is Measured
Eye pressure is measured through a procedure called tonometry. This test is quick and does not cause pain. An eye care professional uses a specialized instrument for this assessment.
One common method involves gently touching the front surface of the eye with a device after numbing eye drops are applied. This device measures the force required to slightly flatten a specific area of the cornea, the clear front part of the eye. Another method, the “air puff” test, uses a rapid pulse of air directed at the eye to measure how much the cornea flattens.
Why Maintaining Normal Pressure Matters
Maintaining eye pressure within a healthy range preserves vision and the health of the optic nerve. The optic nerve transmits visual information from the eye to the brain. When eye pressure is consistently too high, it can place excessive pressure on this nerve, potentially causing damage. This damage can affect vision over time.
If the fluid inside the eye does not drain properly, pressure can build up, which can lead to vision loss. Conversely, eye pressure that is too low, below 5 mmHg, can be problematic. Very low pressure can lead to the eye losing its shape and may impact the retina or optic nerve. This can result in blurred vision or other issues.
Regular eye exams monitor eye pressure and detect potential concerns early. Early detection and management address pressure-related issues and help preserve vision.