Q: With my eye pressures running a little high, my eye doctor makes me take a visual field test twice a year. I hate this test, and wonder if this is really necessary?
A: First, for those who are not familiar, this test actually “maps out” your field of vision for each eye. We may choose to examine just the central 10 degrees of your vision, or perhaps a larger area like 30 degrees, or even the outer edges....your peripheral vision. But the purpose is essentially the same...we are trying to determine if your optic nerve is incurring damage from your elevated eye pressure.
Glaucoma is a disease without symptoms. It is caused by elevated pressure inside your eyes, and/or poor blood flows into the back of the eye. Either way, over time the delicate nerves that exit your eyes in the back, through the optic nerves ( think of a telephone cable carrying signals from your eyes to your brain ) can be damaged. That means that over time you begin to lose your vision. Unfortunately, this vision loss is so slow and totally without pain or blurry vision that a person can lose quite a bit of their visual field before they realize it. And once lost, we have no way to restore it.
The visual field test shows you tiny lights inside a big bowl and your job is to respond each time you see a light blink. It is very tedious and requires a cooperative and motivated patient to get a valid result. Many patients must repeat the field tests until we can prove that damage is or is not occurring to your optic nerve. Virtually no one enjoys doing this totally painless test, but it is essential.
Back when I started my practice, the thinking was that visual field changes or loss were an “early indicator” of glaucoma. We now know that is not true. If we find deficits or areas of vision loss in your field, we now know that this has been occurring for a very long time. In fact, our goal these days is to treat your eye pressures or whatever type of glaucoma you may have early enough to prevent any visual field loss at all! We try to diagnose glaucoma so that you will never notice any change or loss in vision at all.
So the bottom line is that doing your visual field tests to the very best of your ability, and as often as your eye doctor believes necessary is important. The good news is that treating glaucoma is very effective these days, with eye drop medicines usually able to control and prevent vision loss. Keeping your eyesight safe and clear all your life is mostly prevention and regular eye exams.