Ophthalmologists use several tests to screen for and diagnose glaucoma and to monitor response to treatment, including tonometry, ophthalmoscopy, perimetry, and gonioscopy.
This test measures IOP by assessing the amount of force needed to flatten a small area of the cornea. The most effective way to do this is with applanation tonometry. In this test, the eye is numbed with anesthetic eyedrops. Then, slight pressure is applied to the cornea with a small instrument (a tonometer) while the doctor looks through a table-mounted microscope called a slit lamp.
A handheld tonometry device (ICare Tonometer) is sometimes used for testing as well, and it requires no anesthetic eyedrops. It is relatively accurate, although by itself it is not sufficient for an accurate diagnosis. Tonometry is painless and poses virtually no risk to the cornea.
This test is used to inspect the optic nerve, both when making the initial diagnosis of glaucoma and when examining the nerve during treatment. To perform ophthalmoscopy, the doctor dilates the pupils with eyedrops and then uses a specialized microscope (slit lamp) and a small handheld lens to provide a three-dimensional view of the nerve. During this exam, the doctor looks for loss of the structure of the nerve fibers at the optic disc, a condition called cup enlargement or excavation.
Other imaging techniques, for example, laser-based image formation, are used to supplement ophthalmoscopy when confirming a diagnosis of glaucoma.
As with ophthalmoscopy, perimetry is used to help diagnose glaucoma and monitor progression of the disease during treatment. The patient wears a patch over one eye and looks straight ahead at a bowl-shaped white area, while a computer provides lights at various locations around the bowl. The patient indicates each time he or she sees a light. By documenting the lights the patient can see, perimetry provides a map of the visual fields.
The type of vision loss associated with glaucoma is relatively specific, and perimetry can detect the visual field defects that are typical of glaucoma. The test takes approximately four minutes to perform in each eye. Quicker methods of perimetry that take only two minutes per eye are now being used. Among the most promising is frequency doubling technology, which measures damage to the type of cells in the retinaganglion cellsthat appear to be more susceptible than the optic nerve to damage by glaucoma.
Other newer perimetry methods include the use of colored test lights (blue targets on a yellow background).
Laser-based optic head imaging
To supplement the clinical examination of the optic nerve, instruments have been developed that measure the optic nerve's health. These devices enable the ophthalmologist to view and measure the eye's nerve tissues. Each has specific advantages and disadvantages.
This test allows the doctor to view the front of the eye (anterior chamber) to check the angle where the iris meets the cornea. This information helps determine whether you have open- or closed-angle glaucoma. For a gonioscopy, the doctor numbs the eye and places a lens on the front surface. The lens allows the eye doctor, with the use of mirrors, to evaluate the drainage around the eye and to see if any material is clogging the angle.