Ocular Hypertension Overview
The term ocular hypertension usually refers to any situation in which the pressure inside the eye, called intraocular pressure, is higher than normal. Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Ocular hypertension is an eye pressure of greater than 21 mm Hg.
Although its definition has evolved through the years, ocular hypertension is commonly defined as a condition with the following criteria:
- An intraocular pressure of greater than 21 mm Hg is measured in one or both eyes on 2 or more occasions. Pressure inside the eye is measured using an instrument called a tonometer.
- The optic nerve appears normal.
- No signs of glaucoma are evident on visual field testing, which is a test to assess your peripheral (or side) vision.
- To determine other possible causes for your high eye pressure, an ophthalmologist (a medical doctor who specializes in eye care and surgery) assesses whether your drainage system (called the "angle") is open or closed. The angle is seen using a technique called gonioscopy. This technique involves the use of a special contact lens to examine the drainage angles (or channels) in your eyes to see if they are open, narrowed, or closed.
- No signs of any ocular disease are present. Some eye diseases can increase the pressure inside the eye.
Ocular hypertension should not be considered a disease by itself. Instead, ocular hypertension is a term that is used to describe individuals who should be observed more closely than the general population for the onset of glaucoma. For this reason, another term that may be used to refer to an increase in intraocular pressure is glaucoma suspect. A glaucoma suspect is a person whom the ophthalmologist is concerned may have or may develop glaucoma because of the elevated pressure inside the eyes.
As mentioned above, increased intraocular pressure can result from other eye conditions. However, within this article, ocular hypertension primarily refers to increased intraocular pressure but without any optic nerve damage or vision loss. Glaucoma occurs when increased intraocular pressure, optic nerve damage, and vision loss are present.
As of the year 2000, an estimated 2.47 million people in the United States have glaucoma and more than 130,000 are legally blind because of this disease. These statistics alone emphasize the need to identify and closely monitor people who are at risk of developing glaucoma, particularly those with ocular hypertension.
- Studies estimate that 3-6 million people in the United States alone, including 4-10% of the population older than 40 years, have intraocular pressures of 21 mm Hg or higher, without detectable signs of glaucomatous damage using current tests.
- Studies over the last 20 years have helped to characterize those with ocular hypertension.
- Recent data on people with ocular hypertension from the Ocular Hypertension Treatment Study have shown that they have an average estimated risk of 10% of developing glaucoma over 5 years. This risk may be decreased to 5% (a 50% decrease in risk) if eye pressure is lowered by medications or laser surgery. However, the risk may become even less than 1% per year because of significantly improved techniques for detecting glaucomatous damage. This could allow treatment to start much earlier, before vision loss occurs. Future studies will help to further assess this risk of glaucoma development.
- Patients with thin corneas may be at a higher risk for glaucoma development; therefore, your ophthalmologist may use a measuring device, called a pachymeter, to determine your corneal thickness.
- Ocular hypertension is 10-15 times more likely to occur than primary open-angle glaucoma, a common form of glaucoma. That means that out of every 100 people older than 40 years about 10 will have pressures higher than 21 mm Hg, but only 1 of those people will have glaucoma.
- Over a 5-year period, several studies have shown the incidence of glaucomatous damage in people with ocular hypertension to be about 2.6-3% for intraocular pressures of 21-25 mm Hg, 12-26% for intraocular pressures of 26-30 mm Hg, and approximately 42% for those higher than 30 mm Hg.
- In approximately 3% of people with ocular hypertension, the veins in the retina can become blocked (called a retinal vein occlusion), which could lead to vision loss. Because of this, keeping pressures below 25 mm Hg in people with ocular hypertension and who are older than 65 years is often suggested.