Glaucoma refers to a group of eye disorders with a wide range of causes, but which involve damage to the optic nerve and resulting loss of vision. This damage is usually related to elevated fluid pressure in the eye, commonly referred to intraocular pressure or IOP, though there is also a condition known as low-tension glaucoma where the optic nerve is damaged despite normal or below-normal IOP. Glaucoma is the second leading cause of vision loss worldwide, after cataracts. It is sometimes referred to as the “sneak thief of sight” because some forms of glaucoma progress very slowly, so that patients do not seek medical attention until the disease is advanced, by which time the vision loss is irreversible.
Glaucoma related to elevated IOP can be divided into two main categories: open-angle and closed-angle. Of the two, closed-angle glaucoma is less common, accounting for approximately 10% of cases. The “angle” refers to the outer edge of the iris, where it meets the cornea. In a healthy eye, fluid known as aqueous humor flows back and forth through the angle via a structure known as the trabecular meshwork, regulating pressure within the eye. Closed-angle glaucoma occurs when the angle is completely or nearly completely blocked. It can appear suddenly and is often painful; visual loss can progress quickly, but the discomfort often leads patients to seek medical attention before permanent damage occurs. Open-angle, chronic glaucoma occurs when flow of fluid through the trabecular meshwork slows. It tends to progress at a slower rate and patients may not notice they have lost vision until the disease has progressed significantly.
Regardless of the type of glaucoma, the mechanism for vision loss is the same: elevated pressure in the eye causes damage to the optic nerve. Vision loss due to glaucoma is usually irreversible.
How is Glaucoma Detected and Diagnosed?
Glaucoma can be diagnosed in a variety of ways, either directly (by examining the eye itself), or indirectly (by observing symptoms consistent with glaucoma). Direct methods of glaucoma diagnosis include tonometry (direct measurement of IOP using a device called a tonometer) and gonioscopy (examination of the angle using magnification and a mirror). Indirect methods of glaucoma diagnosis include perimetry, also known as a visual field test (testing of peripheral vision to detect vision loss due to glaucoma), optical coherence tomography (abbreviated OCT, a 3-D infrared scan of the retina and macula that can show changes due to glaucoma), and ophthalmoscopy (examination of the optic nerve to detect damage due to glaucoma).
How is Glaucoma Treated?
Glaucoma is treated primarily through either medication or surgery. Glaucoma medications usually take the form of eye drops, functioning either by suppressing production of aqueous humor, or stimulating better flow through the trabecular meshwork. Taken regularly according to the doctor’s instructions, they can be very effective in managing open-angle glaucoma.
Surgical interventions usually involve creating new pathways for drainage of aqueous humor. These can take the form of conventional surgeries, where the trabecular meshwork is physically opened, or tiny catheters implanted. They can also take the form of laser procedures, where holes in the trabecular meshwork, or even the iris, are created using a device called a YAG laser.
Glaucoma and You
It is estimated that three million Americans have glaucoma. It is further estimated that nearly half of those people are unaware of their condition. Because vision loss can be gradual, and because it progresses from the periphery, many people do not seek medical attention until significant vision loss has already occurred.
Glaucoma is both easily detectable and in most cases very treatable. An IOP check and a dilated exam are both considered parts of a comprehensive eye exam, and both are excellent ways to diagnose glaucoma, or even slightly elevated eye pressure that may be an early sign of developing glaucoma. For this reason, it’s a great idea to have a yearly eye examination with a qualified eye care provider.