By James C. Tsai, MD
Last reviewed on October 29, 2017

I've heard that glaucoma is caused by high eye pressure, and that left untreated glaucoma can cause blindness. At what pressure will I go blind?

Glaucoma is a multi-factorial, complex eye disease with specific characteristics such as optic nerve damage and visual field loss. While increased pressure inside the eye (called intraocular pressure or IOP) is usually present, even patients with normal range IOP can develop glaucoma.

There is no specific level of elevated eye pressure that definitely leads to glaucoma; conversely, there is no lower level of IOP that will absolutely eliminate a person’s risk of developing glaucoma. That is why early diagnosis and treatment of glaucoma is the key to preventing vision loss.

Measuring Eye Pressure

Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 12-22 mm Hg, and eye pressure of greater than 22 mm Hg is considered higher than normal. When the IOP is higher than normal but the person does not show signs of glaucoma, this is referred to as ocular hypertension.

High eye pressure alone does not cause glaucoma. However, it is a significant risk factor. Individuals diagnosed with high eye pressure should have regular comprehensive eye examinations by an eyecare professional to check for signs of the onset of glaucoma.

Elevated IOP

A person with elevated IOP is referred to as a glaucoma suspect, because of the concern that the elevated eye pressure might lead to glaucoma. The term glaucoma suspect is also used to describe those who have other findings that could potentially, now or in the future, indicate glaucoma. For example, a suspicious optic nerve, or even a strong family history of glaucoma, could put someone in the category of a glaucoma suspect.

Vision loss from glaucoma occurs when the eye pressure is too high for the specific individual and damages the optic nerve. Any resultant damage cannot be reversed. The peripheral (side) vision is usually affected first. The changes in vision may be so gradual that they are not noticed until a lot of vision loss has already occurred.

In time, if the glaucoma is not treated, central vision will also be decreased and then lost; this is how visual impairment from glaucoma is most often noticed. The good news is that glaucoma can be managed if detected early, and with medical and/or surgical treatment, most people with glaucoma will not lose their sight.