Glaucoma
Glaucoma is a disease of the optic nerve. The optic nerve transmits the images you see from the eye to the brain. It is made up of many nerve fibers (like an electric cable with its numerous wires), and glaucoma damages these nerve fibers which can cause blind areas and vision loss.
Glaucoma Evaluation
During a glaucoma evaluation, your ophthalmologist will perform the following tests:
Tonometry:
Your doctor measures the pressure in your eyes (intraocular pressure, or IOP) using a technique called tonometry. Tonometry measures your IOP by determining how your cornea responds when an instrument presses on the surface of your eye. Eye drops are usually used to numb the surface of your eye for this test.
Gonioscopy:
For this test, your doctor inspects your eye’s drainage angle – the area where fluid drains out of your eye. During goinoscopy, you sit in a chair facing the microscope used to look inside your eye. You will place your chin on a chin rest and your forehead against a support bar while looking straight ahead. The goniolens is placed lightly on the front of your eye, while your doctor looks through the microscope at the drainage angle. Drops will be used to numb the eye before this test.
Ophthalmosocopy:
With this test, your doctor can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). A good fundus exam under 3D, high magnification is the best screening method to catch glaucoma. The pupils should be dilated for this exam.
Photography:
Sometimes photographs or other computerized images are taken of the optic nerve to record the appearance of your optic nerve. This way, as your eye doctor follows you over the years, he or she can compare the images to observe any changes or glaucoma damage. Many doctors take the photos periodically as a way to detect subtle changes.
Special imaging (OCT):
Different scanners may be used to determine the configuration of the optic nerve head or retinal nerve fiber layer.
Visual Field Testing:
Because it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams.
One particular test, called a visual field test (or “perimetry test”), measures the sensitivity to light at many points in your vision. A typical field test for glaucoma measures the central 60 degrees. A visual field test can help find certain patterns of vision loss and is a key way to check for glaucoma or progression of glaucoma.
To take this test, you sit at a machine with a bowl shape called a perimeter. While you stare at the center of the bowl, lights flash. Each time you see a flash you press a button. A computer records whether you pressed the button when the light flashed in that location. At the end of the test, a printout shows the sensitivity to light at multiple points in your field of vision. This test shows if you have any areas of vision decrease or loss. Loss of visual field is often an early sign of vision loss from glaucoma. Regular perimetry tests are an important technique for learning how, if at all, your vision is changing over time. It can also be used to see if treatment for glaucoma is working to prevent further vision loss.
During the test it is important to hold still and concentrate on the target on which the technician asks you to focus. If you need a break or are uncomfortable, please tell the technician. This will help ensure accurate results. It is important to realize that, with most visual field tests, you are not supposed to see every light, each time it is presented. The machine deliberately shows you lights it is pretty sure you cannot see.
Each of these evaluation tools is an important way to monitor your vision to help ensure that glaucoma does not rob you of your sight. Some of these tests will not be necessary for everyone. Your ophthalmologist or optometrist will discuss which tests are best for you. Some tests may need to be repeated on a regular basis to monitor any changes in your vision caused by glaucoma.