What Is Considered Normal Eye Pressure?

May 3, 2021 | Optometry

What Is Considered Normal Eye Pressure?

Where there are fluids, there’s pressure affecting them. We’re concerned with our blood pressure and the air pressure in our tires. Sometimes less apparent to eye patients is the pressure of the intraocular fluid in their eyes. When intraocular pressure exceeds acceptable parameters, optic nerve damage can cause glaucoma and ensuing permanent vision loss. While there is no magic number for intraocular pressure, the eye-care community has established a range for what is considered normal eye pressure and what to do when pressure falls outside that range.

The Acceptable Range

Ophthalmologists measure intraocular pressure with a tonometer, which they keep sanitary with tonometer tip covers. This device reports pressure in millimeters of mercury (mmHg), just as a barometer does for air pressure or a sphygmomanometer does for blood pressure. Most ophthalmologists believe that intraocular pressure readings should fall between 10 and 20 mmHg. When intraocular pressure lies outside this acceptable range, ophthalmologists will have to medically or surgically intervene to restore normal pressure and protect a patient’s delicate vision.

What Happens When Pressure Is Too High?

As with blood pressure, ocular hypertension is far more common than hypotension. Unlike high blood pressure, however, high eye pressure has no readily apparent symptoms—when optic nerve damage begins to encroach upon peripheral vision, it’s already too late. When intraocular pressure exceeds 20 mmHg, ophthalmologists have cause for concern and will begin exploring strategies to reduce intraocular pressure and prevent further damage to the eyes and optic nerve. The most common approach is to prescribe eye drops, which will encourage increased drainage. In more extreme cases, ophthalmologists may recommend a surgical procedure known as selective laser trabeculoplasty. When eyedrops fail or cause unacceptable side effects, laser treatment can modify eye tissue to better facilitate drainage of the eyes’ aqueous and vitreous humors.

What Happens When It’s Too Low?

Though it’s less common for IOP to dip beneath 10 mmHg and below what is considered normal eye pressure, low pressure can present problems of its own. The eye relies on a certain degree of pressure in circulation to maintain the spherical shape of the eye and the functions of the retina and lens. Insufficient intraocular pressure causes vision to blur and distort as parts of the eye go out of alignment. Low pressure in the eye most often occurs as a hypercorrection for high IOP—in other words, the medication and surgery are too effective for their own good. When IOP is below 5 mmHg, this condition is known as ocular hypotony and needs to be corrected.