Normal-Tension Glaucoma Overview
Glaucoma is usually high pressure inside the eye that damages the optic nerve and can result in permanent vision loss. Normal-tension glaucoma (also called low-tension glaucoma) is a unique condition in which optic nerve damage and vision loss have occurred despite a normal pressure inside the eye.
Eye pressure, called intraocular pressure (IOP), is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Most people with glaucoma have IOP of greater than 21 mm Hg; however, in normal-tension glaucoma, people have IOP within the normal range.
By definition, people with normal-tension glaucoma have open, normal-appearing angles. In fact, the features of normal-tension glaucoma are similar to primary open-angle glaucoma (POAG), the most common form of glaucoma (see Primary Open-Angle Glaucoma).
- Although the occurrence of normal-tension glaucoma varies worldwide, it is very prevalent in Japan.
- In the United States, up to 15-25% of people with open-angle glaucoma experience normal-tension glaucoma.
- According to the Baltimore Eye Study, 50% of individuals with changes in their optic disc (the front surface of the optic nerve) and in their visual field had an IOP of less than 21 mm Hg on a single visit, and 33% had an IOP of less than 21 mm Hg on 2 measurements.
- Normal-tension glaucoma is more common in women than in men.
- Normal-tension glaucoma affects adults, with an average age of 60 years.
Normal-Tension Glaucoma Causes
Although its cause is not completely understood, normal-tension glaucoma is generally believed to occur either because of an unusually fragile optic nerve that can be damaged despite a normal pressure inside the eye or because of reduced blood flow to the optic nerve.
- Unusually fragile optic nerves may be inherited.
- Reduced blood flow to the optic nerve can be due to disorders of the blood vessels (called vascular diseases), including vasospasms and ischemia.
- Vasospasms are spasms or constrictions of the blood vessels.
- Ischemia is reduced oxygen delivered to the tissue, in this case the optic nerve, because the blood vessels are either narrowed or obstructed.
Medically Reviewed by a Doctor on 12/29/2015
Francisco Talavera, PharmD, PhD