Glaucoma Prevention and Treatment

by Food and Drug Administration (FDA)

An outstanding scholar still in his 30s, John felt his "sight getting weak and dull" — occupational eyestrain, he supposed. Soon his left eye dimmed, starting from the left side. Then his right eye failed, "perceptibly and gradually over three years." By age 43, he was totally blind.

That was in 1652. John Milton triumphed over blindness, still serving the British foreign office and writing literary classics like "Paradise Lost." Yet he never ceased lamenting "how my light is spent/Ere half my days, in this dark world and wide."

What relegated him to seeing "a universal blank" was probably open-angle glaucoma, which today needlessly blinds 80,000 Americans each year. It causes another 900,000 to lose some vision. Yet now we have means Milton lacked to thwart "the sneak thief of sight" with a number of treatments approved by the Food and Drug Administration.

Glaucomas are a group of diseases sharing certain features, commonly including high intraocular pressure (IOP), damaged optic nerves, and loss of peripheral vision. Early detection can contain two glaucomas: chronic (sometimes called common) and acute.

Primary open-angle glaucoma (chronic glaucoma) affects mostly adults over age 35. This most prevalent glaucoma is the sneak-thief disease without noticeable symptoms. By the time it's detected, it has started doing damage.

The uncommon primary angle-closure glaucoma (acute glaucoma) may seem the opposite of common glaucoma, erupting in a sudden, violent attack. It's also possible to get both common and acute ("combined-mechanism") glaucoma together. The unusual low-pressure glaucoma is another variant. Regular eye examinations can help protect against the onset of open-angle and closed-angle glaucomas.

The cornea is the clear outer covering of the eye. Separating it from the iris (the colored part) is the anterior chamber, a space filled and inflated by aqueous humor. This fluid (unrelated to the tears which bathe the outside surface of the cornea) originates in the ciliary body just behind the iris. It circulates in the anterior chamber, nourishing the eye's delicate tissue and keeping it from collapsing, at a pressure usually measuring between 10 and 20 millimeters of mercury. To maintain equilibrium, the aqueous humor drains through a porous tissue in the angle in front of the iris, where it meets the cornea, called the trabecular meshwork.

If the aqueous humor cannot drain properly, either because the drainage canals become clogged (as in chronic glaucoma) or because the iris is pushing against the cornea (as in angle-closure glaucoma), it backs up, exerting pressure on the gel in the vitreous cavity at the center of the eye. Eventually the building pressure affects the delicate optic nerve at the rear. Since the optic nerve transmits visual images to the brain, damage to parts of it correspondingly reduces vision.

Pressure over 21 millimeters may prompt concern, while pressure over 24 mm can indicate glaucoma level — but not always. These measures are not absolute. Some individuals tolerate higher pressures than others. Half the people with undiagnosed glaucoma have pressures below 22 mm, while others with higher pressures never develop glaucoma, with optic nerve damage causing loss of vision. Low-pressure glaucoma can be especially elusive. Moreover, tonometry (the measurement of eye pressure) can be affected by many factors, even by the time of day (IOP measuring highest in the morning).

Tonometry measures the force necessary to indent the eye. One method is to anesthetize the eye, then press a tonometer onto it. Another is to measure the force needed for a puff of air to indent the cornea.

While widespread eye-puff testing at health fairs detects pressure levels, a more thorough examination calls for an ophthalmoscopic test enabling doctors to see into your eye to examine the optic nerve for damage or a high ratio of its central cup to the surrounding disc. (See accompanying article.) They must also take personal characteristics into account in evaluating an individual's risk of glaucoma.

Chronic (Primary Open-Angle) Glaucoma

Physicians do not like to begin therapy prematurely in individuals identified as at risk for chronic glaucoma. Patients considered "pre-glaucoma" should have their eyes examined as often as their doctors think necessary.

Increasingly frequent dosages of medications may be needed as the eye develops tolerance to the medicine. Drug therapy can effectively thwart the progress of glaucoma, but it can mean taking an escalating variety of eye drops and pills, with various side effects, for life.

Topical medications for glaucoma are serious medicine, not to be confused with over-the-counter eye drops for easing common eye irritations. The most popular maintenance eye drop, Timoptic (timolol maleate), may have side effects on the nerves, digestion, vision, skin, respiration, and heart of some individuals. Timoptic is a beta-blocker eye drop. Taken usually twice daily, beta blockers decrease production of aqueous humor. Side effects may include lowered pulse rate and blood pressure, exacerbated asthma, and fatigue. In June 1995, British researchers reported that drops in this class may be related to breathing impairment in elderly people with previously unrecognized respiratory problems.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.