Why is Glaucoma such a devastating disease? Well, two reasons. The first, of course, is that it robs you of your vision. The second is that this "thief" steals your vision slowly and painlessly, and you may not even know you have glaucoma until it's too late!
Your peripheral, or side vision is the first part of your vision to be lost in glaucoma. This is one of the reasons it's so hard to know that you have the disease, because your central vision, the vision you read and drive with, is preserved until very late in the disease.
We measure your side vision with a test called a "Visual Field" or Perimetry test. Modern testing is computerized. You place your chin on a chin rest and look into a dim, white bowl. When you see a light come into view you press a button. The readout looks like this:
In the early stages you might only lose a very small portion of your vision.
In very late stages much of your side vision is gone; it can be like looking through a tunnel.