It is important to note, that nearly 20% of individuals with glaucoma do not demonstrate elevated pressures. These patients have what is known as either Low Tension Glaucoma or Normal Tension Glaucoma. These are both names for a condition that results in optic nerve damage in the absence of significantly elevated eye pressure. In these patients, the eye pressure is higher than a particular patient can tolerate. Every patient has a range of “target pressures” that is deemed to be “safe” for them. The “target pressure” can vary from patient to patient.
How Intraocular Pressure is Measured
Intraocular pressure is measured in millimeters of mercury (mm Hg). Normal eye pressures usually range from 10 to 20 millimeters of mercury (10-20mm Hg.) When the eye pressure rises above 20mm Hg, the eye becomes at risk for glaucoma. Patients with Low Tension Glaucoma or Normal Tension Glaucoma can develop optic nerve damage even if their eye pressure is 20mm Hg or below.
Ocular Hypertension
Some patients have elevated eye pressures but do not develop glaucoma. These patients are said to have Ocular Hypertension. In these patients, the optic nerve appears to be able to withstand higher than normal eye pressures (above 20mm Hg.) Ocular hypertensive patients can have pressure in the 30’s yet still not show any evidence of optic nerve damage.