Testing for Glaucoma
The optic nerve is the part of the eye which is most affected in glaucoma. The optic nerve is not a "single" nerve, but a collection of approximately 1,000,000 (one million) nerve fibers. Normally, every human loses 500 fibers a year through normal aging. It is the only living nerve in the human body which can be seen without making an incision. The optic nerve is similar in many ways to the film in a camera. The optic nerve is the structure that sees images and tells the brain what the eyes are seeing. When glaucoma injures these nerve fibers, eventually killing some of them, it causes loss of vision. When the doctors detect nerve damage, this early damage is the first stage of glaucoma. Damage to the optic nerve is permanent and can not be reversed. Some doctors believe that the more damage that has already occurred, the easier it is for further damage to develop. Once the optic nerve is totally destroyed, an eye can not detect light.
The optic nerve is located in the back of the eye, behind the pupil. Normally if one shines a light on the pupil, the pupil constricts. This makes it extremely difficult, if not impossible, to adequately examine the optic nerve's structure. Our doctors, therefore, need to put dilating drops in the eye. These drops temporarily enlarge the pupil, or the window to the optic nerve, and usually last a matter of hours. They not only make things seem brighter, but can also cause images to seem blurrier.
The doctors need to examine both the way the optic nerve looks and the way it functions. This helps them decide whether there is glaucoma, and whether there has been any change or damage to the optic nerve. The doctor will either sketch the appearance of your optic nerve, take photographs of it, or both.
The doctors measure the function of your optic nerve by having you perform a visual field test. This test measures your side vision. This is important because the area of visual loss begins in the side vision and is not noticed by patients until glaucoma becomes very advanced. Our doctors hope to stop the damage before it gets very advanced, or if you already have advanced damage, we hope to prevent it from worsening.
Visual field testing requires a great deal of concentration. The test is designed to detect the dimmest light that you can see. You will only see one-half of the objects presented by the machine. This can be frustrating and frightening. It is also a boring test. Remember, if you are having trouble with the testing, or are tired, ask the technician to stop and explain the test to you again, or give you a rest!
If glaucoma worsens, visual field defects get larger and leave a patient with tunnel vision, not being able to see things to the side. It can cause a person to bump into objects or stumble and fall.
Under proper management and with good patient cooperation, it is very unlikely for a patient to go blind from glaucoma. Careful follow-up and good patient compliance severely limit the risk of marked visual loss.
Many different types of optic nerve imaging are available and we use many of them to help us make the diagnosis and to follow your eyes ensuring there is no progression.