Normal Tension Glaucoma
How does normal tension glaucoma differ from "regular" glaucoma? Glaucoma is a group of eye diseases that usually share common traits, such as high intraocular pressure (IOP or eye pressure), damage to the optic nerve and gradual sight loss. Most kinds of glaucoma involve elevated eye pressure. However, glaucoma can sometimes strike without any increase in eye pressure.
Normal tension glaucoma (NTG), also known as low tension or normal pressure glaucoma, is a form of glaucoma in which damage occurs to the optic nerve without eye pressure exceeding the normal range. In general, a "normal" pressure range is between 10-20 mm Hg.
What causes normal tension glaucoma?
The causes of NTG are still unknown. For some reason, the optic nerve is susceptible to damage from even the normal amount of eye pressure. Researchers continue to examine why some optic nerves are damaged by these relatively low eye pressure levels.
How is normal tension glaucoma diagnosed?
NTG is diagnosed by observing the optic nerve for signs of damage. This can be done in one of two ways. In one procedure, an instrument called an ophthalmoscope is held close to the eye. In a darkened room, the light from the ophthalmoscope allows the doctor to look through the pupil and examine the shape and color of the optic nerve. A nerve that is cupped or is not a healthy pink color is a cause for concern.
A second procedure is the visual field test. This test produces a map of the patient’s complete field of vision. Using this test, the doctor can check for any areas of sight loss that may be caused by damage to the optic nerve. This would appear as slight changes in the person’s vision occurring anywhere from near the center to the edge of the field of vision. These changes are not necessarily noticeable to the patient.
What are the risk factors for NTG?
Some risk factors for NTG include:
- Family history of any kind of glaucoma-it doesn’t have to be normal tension glaucoma
- Japanese ancestry
- Cardiovascular disease
In North America, normal tension glaucoma is more prevalent in women than in men.
How is NTG treated?
Since so little is known about why normal eye pressure damages some eyes, most doctors treat normal tension glaucoma by reducing the eye pressure as low as possible using medications, laser treatments and filtering surgery. Over the last decade, a Glaucoma Research Foundation study has shed some light as to the benefits and drawbacks of lowering eye pressure to the low normal range, instead of the mid or high normal range.
Thanks to Douglas R. Anderson, MD, Professor of Ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, for contributing to this article.
Last reviewed on December 13, 2010