Because it has no noticeable symptoms, glaucoma is a difficult disease to detect without regular, complete eye exams.
During a glaucoma evaluation, the doctor will perform the following tests:
The 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 (or sometimes a puff of air) presses on the surface of your eye. Eyedrops are usually used to numb the surface of your eye for this test.
For this test, the doctor inspects your eye’s drainage angle—the area where fluid drains out of your eye. During gonioscopy, 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, and a narrow beam of light is directed into your eye while your doctor looks through the slit lamp at the drainage angle. Drops will be used to numb the eye before the test.
With this test, the doctor can evaluate whether or not there is any optic nerve damage by looking at the back of the eye (called the fundus). With ophthalmoscopy, the doctor uses a powerfully magnified light that magnifies up to about 15 times. This type of ophthalmoscopy is most commonly done during a routine physical examination. Ophthalmoscopy allows a better view of the fundus, even if your natural lens is clouded by cataracts.
Visual field test
A visual field test (perimetry test), measures all areas of your eyesight, including your side, or peripheral, vision. A visual field test can help find certain patterns of vision loss and is a key way to check for glaucoma. It is very useful in finding early changes in vision caused by nerve damage from glaucoma.
To take this painless test, you sit at a bowl-shaped instrument 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 the location of each flash and whether you pressed the button when the light flashed in that location. At the end of the test, a printout shows if there are areas of your field of vision where you did not see the flashes of light. This test shows if you have any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma. Visual field testing is used together with the clinical exam and HRT testing to determine if you have glaucoma or if your glaucoma is worsening.
Sometimes photographs or other computerized images are taken of the optic nerve to inspect the nerve more closely for damage from elevated pressure in the eye.
Optical Coherence Tomography
Optical coherence tomography (OCT) is a special scan used to study the anatomy of the retina and optic nerve in fine detail.
OCT testing requires dilation of the pupils but does not require a needle in the arm and does not involve touching the eye. A healthy retina is only ¼ of a millimeter thick, but it contains multiple layers of specialized cells. One layer converts light into nerve signals, another processes the nerve impulses, while another transmits these processed impulses to the brain where they are interpreted.
OCT testing is like having an optical biopsy of the retina and optic nerve; it provides excellent visualization of these structures, and aids greatly in the diagnosis and treatment of glaucoma.
Not every patient needs an OCT test. In Ontario OCT testing is now covered by OHIP.
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. the doctor 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.