When looking into my dilated eyes, the doctor said it looks like I have glaucoma -- the optic nerve is damaged. However, my eye pressure is normal, between 17-20, and a visual field test showed no vision loss. My concern is this: If my optic nerve is damaged, why don't they start glaucoma treatment now instead of waiting for vision loss? Is there any condition other than glaucoma that could have damaged my optic nerve?

Debbie

Glaucoma is a condition in which the optic nerve -- the "cable" that carries visual information from the eye to the brain -- becomes damaged, presumably due to elevated intraocular pressure. Normal eye pressure is considered to be less than 21 mmHG. However, many people who have eye pressures above 21 do not have optic nerve damage. Also, as seems to be your case, people can have eye pressures that are lower than 21, but still have optic nerve damage.

Damage to the optic nerve can cause loss of vision, beginning with the loss of peripheral vision. A visual field test is performed in the eye doctor's office, which will pick up visual field loss from glaucoma. During an eye exam, the eye pressure is checked and the optic nerve is examined. A normal-looking optic nerve appears like a white disc with a small, central depression. Damage to the optic nerve can be seen as enlargement of the central depression of the optic nerve, or "cupping." Very severe glaucoma causes the optic nerve to be completely cupped.

As your situation shows, diagnosing glaucoma can sometimes be difficult. Some people can be born with optic nerves that have moderate cupping, and it is difficult to know whether the cupping is normal or is due to glaucoma. In these situations, the eye pressure, visual field test and optic nerve appearance are carefully monitored. Since glaucoma medications can have side effects, and the disorder usually progresses slowly, most doctors choose to carefully monitor patients who have moderate optic nerve "cupping," but normal eye pressure and visual fields. If the eye pressure rises, or if there is a change in the optic nerve appearance or visual field test, then the doctor will initiate the use of glaucoma eyedrops.

That said, there are some doctors who prefer to start glaucoma eyedrops earlier. Their reasoning is that visual field abnormalities occur only after there has been moderate damage to the optic nerve. By intervening early, they think it may be possible to prevent further damage to the optic nerve, thus averting significant vision loss.

Armed with this information, you should be able to discuss your condition more carefully with your ophthalmologist, or perhaps seek a second opinion.