Glaucoma is a disease that is more common than many people think. The term “glaucoma” represents a condition of high pressure inside the fluid of the eye. Most of the time, especially in its early stages, it has no symptoms but gradually causes loss of vision. Certain kinds of glaucoma can come on suddenly, leading to a red, painful eye and impaired vision.
The test used to screen for glaucoma is called ocular tonometry. It measures the intraocular pressure or IOP of the eye. Ideally, people over the age of forty should see the eye doctor every year for a glaucoma screening with a tonometer. The test gives a measurement in mmHg or millimeters of mercury.
There are several different kinds of tonometry the doctor can use. In applanation tonometry, force is applied to the eye and a measurement is taken to see how much force is necessary to flatten a constant area of the corneal surface. A topical anesthetic is applied to the surface of the eye so the probe can painlessly come in contact with it.
The best test for determining ocular pressure is called Goldmann tonometry. It is the most commonly used test for glaucoma screening. It involves a prism mounted on the tonometer. The prism is place on the cornea of the eye. The force is applied to the corneal surface and the pressure required to flatten the cornea is determined. While it’s a good test, it is an imprecise test, as is true of all glaucoma screening tests.
The Perkins tonometer is a type of applanation tonometer that is portable. It is one of the best tests for evaluating glaucoma in children and doesn’t require a slit lamp examination or any kind of anesthesia.
The dynamic tour tonometry doesn’t use the application of applanation. Instead it uses contour matching techniques. There is a hollow tip used that is the same shape of the cornea. There is a pressure center in the center of the tip that determines the degree of pressure inside the eye. The dynamic contour tonometry relies on a normally contoured cornea and doesn’t work as well if the curvature of the cornea is abnormal. It takes about eight seconds of contact on the cornea in order to get an accurate result.
Doctors can use non-contact tonometry, also called air puff tonometry. A quick puff of air is used to flatten the corneal surface. The degree of flattening is determined by an electro-optical system. This noncontact method is considered simple and fast—convenient enough to use in an optometrist’s or ophthalmologist’s office.