DEAR DOCTOR K:
At my last appointment, my ophthalmologist mentioned something about elevated eye pressure. What could this mean?
Elevated eye pressure is often — but not always — associated with glaucoma. Glaucoma is a group of eye diseases that cause vision loss by damaging the optic nerve, which transmits visual information from the eye to the brain.
How does elevated eye pressure (also called intraocular pressure) damage the optic nerve? Normally, a clear liquid called the aqueous humor circulates through the eye, helping to maintain the eye’s shape and pressure. Eventually, the liquid passes through a sieve-like system of tissues and drains out of the eye. Here is an illustration of this process:
In glaucoma, this drainage system breaks down, slowing or blocking the outflow of fluid. The fluid backs up and pressure rises inside the eye.
Why is this? Imagine filling a balloon with water. Say you’re squirting water into the balloon with a turkey baster and pinching the opening of the balloon to keep the water inside. There’s just a little amount of water in the balloon. When you loosen the opening, water will dribble out because there’s not much water pressure inside.
But say you fill the balloon until you think it’s close to bursting. Now when you unpinch the opening, water will shoot out — the more water inside the balloon, the greater the water pressure. It’s the same with your eyeball.
When pressure builds inside the eye, this puts pressure on the optic nerve. If the pressure continues, optic nerve fibers begin to die off and vision fades. This damage is irreversible.
Eye pressure is measured during any standard eye exam. Elevated pressure can indicate glaucoma — but not everyone with slightly elevated pressure will get glaucoma. That’s because the amount of stress the optic nerve can withstand differs for each person and each eye.
Just as not everyone with slightly elevated pressure will get glaucoma, it’s also true that some people with normal pressures will get glaucoma. Their optic nerves are unusually susceptible to what in most people are normal pressures.
That’s why your eye doctor would not only have measured your pressures. He or she also would have looked for additional signs of glaucoma. For example, if the front surface of your optic nerve, called the optic disc, was affected by glaucoma, the doctor would have seen “deep cupping.” A deeply cupped disc appears indented and more pale and yellow than normal. It means that, whatever the pressure in your eye is, the optic disc (optic nerve) is being damaged.
If you do have (or later develop) glaucoma, topical medications — eye drops or ointments — can help to control eye pressure and stop the progression of the disease. You should also have two to four eye examinations per year to make sure the disease is not progressing. If it is, you may need more aggressive treatment.