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What is tonometry used for?
Tonometry is an essential component of the global examination in all eye check-ups and specifically for a glaucoma examination. A complete glaucoma examination has a number of important components.
These tests together give a complete picture of the patient's ocular health and therefore the risks for developing or controlling a given disease such as cataracts, macular degeneration, or glaucoma. The following tests make up a glaucoma examination:
- medical and ocular history
- visual acuity testing
- refraction to measure the glasses or lens correction
- tonometry testing for IOP
- Slit lamp biomicroscope examination is the "stethoscope" of the eye doctor. This high-quality optical device allows the doctor to view the eyes in stereo under high magnification while the patient places their chin on a rest and their forehead against a bar to maintain consistent positioning. Numerous details can be discerned by the trained observer, rendering possible a specific diagnosis, including the etiology (or cause) of an individual patient's glaucoma.
- gonioscopy to examine the aqueous humor outflow channels
- peripheral visual field testing
- Optic nerve head photography is taken by high-quality cameras and recorded, usually digitally. This allows precise comparison from year to year, permitting analysis of subtle anatomical changes over time.
- Optic nerve head topography creates a precise digital image of the nerve thickness around the optic nerve to within 1/1000 of a millimeter. Subtle loss of nerve thickness indicates the progression of glaucoma.
Once the examinations have been completed, a decision is made as to whether or not glaucoma treatment should be given, maintained at its current level, or modified. If the patient is doing well, then glaucoma treatment may be withheld or cut back. If the patient is doing poorly, then more treatment may be recommended. There are several approaches to glaucoma treatment, any or all of which may be appropriate for a given patient. These include but are not limited to the following:
- topical eye drop medications: beta blockers, prostaglandins, alpha agonists, aqueous suppressants, and miotics
- oral ocular hypotensive or pressure-lowering medications: most commonly acetazolamide (Diamox) or methazolamide (MZM).
- laser treatment: SLT (selective laser trabeculoplasty) or ALT (argon laser trabeculoplasty) for open-angle glaucoma and PI (peripheral iridotomy) for closed-angle glaucoma
- filtering procedure: Traditional trabeculectomy surgery permits drainage of the aqueous humor in the front of the eye to a bubble or bleb on the conjunctiva, or clear surface over the white part of the eye. This surgery has been performed for centuries and has been highly perfected under the outstanding control of the operating-room microscope by skilled surgical hands.
- shunting procedure: The eye doctor places a plastic tube and emptying chamber into the eye in the operating room. Commonly used devices include the Molteno shunt, the Express shunt, the Baerveldt valve, and the Ahmed valve. This procedure accomplishes the same effect as the trabeculectomy but generally lasts longer because the plastic tube avoids closure by normal progressive tissue scarring.
- outflow enhancement procedures: These include the viscocanalostomy or the canaloplasty operations that allow the drainage of aqueous humor without a conjunctival bleb or plastic drainage device. Instead, the natural drainage pathways in the anterior or front of the eye are opened surgically, allowing more facile egress of aqueous into the channels of the ocular surface and orbit, or eye socket.
- Newer oral medication strategies to preserve or enhance optic nerve head function: These include antioxidants such as ginkgo biloba or prescription neuro-protectants such as memantine (Namenda).
The bottom line for any patient, and particularly the patient who might be at risk for glaucoma, is to have regular visits to your eye doctor. Patients over the age of 50, or patients at risk of glaucoma over the age of 40, should have regular annual eye examinations.
Medically Reviewed by William Baer, MD; Board Certified Ophthalmology
"Open-angle glaucoma: Epidemiology, clinical presentation, and diagnosis"