Glaucoma refers to a group of related eye disorders that all cause damage to the optic nerve that carries information from the eye to the brain. Glaucoma usually has few or no initial symptoms.
In most cases, glaucoma is associated with higher-than-normal pressure inside the eye ? a condition called ocular hypertension. But it also can occur when intraocular pressure (IOP) is normal. If untreated or uncontrolled, glaucoma first causes peripheral vision loss and eventually can lead to blindness.
According to the American Academy of Ophthalmology, the most common type of glaucoma ? called primary open-angle glaucoma ? affects an estimated 2.2 million people in the United States, and that number is expected to increase to 3.3 million by 2020 as the U.S. population ages.
And because most cases of glaucoma have few or no early symptoms, about half of Americans with glaucoma don't know they have it.
Glaucoma is the second-leading cause of blindness in the U.S. (behind macular degeneration) and India, and the second-leading cause of blindness worldwide (behind cataracts).
Diagnosis, Screening and Tests for Glaucoma
During routine eye exams, a tonometer is used to measure your intraocular pressure, or IOP. Your eye typically is numbed with eye drops, and a small probe gently rests against your eye's surface. Other tonometers send a puff of air onto your eye's surface.
An abnormally high IOP reading indicates a problem with the amount of fluid (aqueous humor) in the eye. Either the eye is producing too much fluid, or it's not draining properly.
Normally, IOP should be below 21 mmHg (millimeters of mercury) ? a unit of measurement based on how much force is exerted within a certain defined area.
If your IOP is higher than 30 mmHg, your risk of vision loss from glaucoma is 40 times greater than someone with intraocular pressure of 15 mmHg or lower. This is why glaucoma treatments such as eye drops are designed to keep IOP low.
Other methods of monitoring glaucoma involve the use of sophisticated imaging technology ? such as scanning laser polarimetry (SLP), optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy ? to create baseline images and measurements of the eye's optic nerve and internal structures.
Then, at specified intervals, additional images and measurements are taken to make sure no changes have occurred over time that might indicate progressive glaucoma damage.
Visual field testing is a way for your eye doctor to determine if you are experiencing vision loss from glaucoma. Visual field testing involves staring straight ahead into a machine and clicking a button when you notice a blinking light in your peripheral vision. The visual field test may be repeated at regular intervals to make sure you are not developing blind spots from damage to the optic nerve or to determine the extent or progression of vision loss from glaucoma.
Gonioscopy also may be performed to make sure the aqueous humor (or "aqueous") can drain freely from the eye. In gonioscopy, special lenses are used with a biomicroscope to enable your eye doctor to see the structure inside the eye (called the drainage angle) that controls the outflow of aqueous and thereby affects intraocular pressure. Ultrasound biomicroscopy is another technique that may be used to evaluate the drainage angle.