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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.
Timoptic's century-old predecessor, pilocarpine, requires more frequent use to do its job, increasing drainage of aqueous fluid in both open- and closed-angle glaucomas. Pilocarpine is a miotic, designed to increase aqueous fluid drainage. Because miotics work by making the pupil smaller, they can result in dim vision and may increase the risk of cataracts.
Another class of medications, adrenergic agonists, such as epinephrine, also increases aqueous humor drainage, with possible side effects of allergic reactions, blurred vision, headache, and increased heart rate. Alpha adrenergic agonists decrease aqueous humor production after surgery or aid patients taking maximum dosages of other medications. Side effects include red eyes, allergic reactions, and dry mouth.
Diamox carbonic anhydrase inhibitor tablets, like beta blockers, decrease production of aqueous fluid, but these drugs seem to provoke more prominent side effects in some people, including mental depression, kidney stones, tingling in the hands and feet, and sometimes anemia.
FDA's May 1995 approval of a Carbonic Anhydrase Inhibitor in eye drop form as Trusopt (dorzolamide) provides a medication that may have fewer and reduced incidence of these severe side effects.
Since reactions to medications vary so much from person to person, a drug that causes one individual problems may be easily tolerated by another. An appropriate drug regimen, therefore, needs to be worked out carefully between patient and health professional.
Glaucoma medications are potent drugs. Those who take them should consult a pharmacist to be certain that they won't interact adversely with any other prescriptions or over-the-counter drugs being taken. For example, some over-the-counter products, including decongestants, may not be suited for people at risk of glaucoma.
Acute (Closed-Angle) Glaucoma
A century after Milton gradually lost his sight, composer Johann Sebastian Bach went blind in a violent flash, probably from acute (closed-angle) glaucoma. Bach thought he aggravated his weak vision by a lifetime of copying music in the dim light of church organ lofts; his portrait shows a characteristic squint. Though a surgeon claimed to have operated successfully on Bach's eyes, the composer's vision failed again in a few days. He died a few months later, after a futile--and possibly harmful--second operation.
Acute glaucoma may seem the opposite of open-angle because it erupts in violent attacks and intense pain, rather than emerging subtly. Yet patients may not notice minor preliminary episodes, which pave the way for serious seizures. People beset by a major seizure must get to an ophthalmologist, or at least a hospital emergency room, promptly to save their vision.
Monitoring can protect people prone to acute glaucoma from major attacks.
Acute glaucoma attacks are emergencies because aqueous fluid gets trapped in the angle of the eye suddenly. Having nowhere to go, its abrupt backup can damage the optic nerves, eventually squashing them irreparably.
Regular, thorough eye checkups can detect the risk of acute glaucoma. High IOP, family history, and other indicators resemble those for common glaucoma, but very farsighted people and those of Asian descent are most vulnerable to angle-closure glaucoma. Once a major angle-closure attack seems imminent, preventive laser surgery is advisable, since an attack can damage the eye quickly.
Regular monitoring of people diagnosed with narrow-angle conditions looks for increased IOP or tissue damage. Telltale symptoms of an attack include blurred vision, halos around lights, and eye pain sharp enough to induce vomiting. The eye becomes reddened, feeling as if it could burst (though it can't). Persons experiencing such attacks should go immediately to an ophthalmologist or an emergency room, ideally calling in advance to ready staff to receive a case of closed-angle, acute glaucoma.
Emergency procedures use eye drops and clinical eye massage to reduce IOP and prevent the eye from hardening. Once stabilized, the patient may have laser surgery to create an artificial opening for aqueous fluid to drain. Acute glaucoma usually attacks one eye before the other, so laser surgery on the unaffected eye may be recommended at the time to forestall a second attack there.
Laser Surgery
Some patients may require traditional scalpel surgery, but in recent years laser operations have come into favor. Laser surgery can't repair existing damage, but it usually stops glaucoma, both in acute emergencies and open-angle cases. It may involve minor side effects, including restrictions on wearing contact lenses, but its risks are quite low. Sometimes it must be repeated if its drainage openings begin to close.
Light amplification by stimulated emission of radiation--LASER--sends a uniform, focused beam of light to pinpoint applications. In glaucoma surgery for angle closure, the laser creates a minute hole in the iris, just large enough to allow aqueous fluid to flow freely.
Despite its high-tech wizardry, most laser surgery for glaucoma seems quite undramatic to the patient undergoing it. (See "Light for Sight," FDA Consumer, July-August 1990.) An acute glaucoma patient peers into the eyepiece on one side of a boxy device while a surgeon manipulating controls peers into an eyepiece opposite. There's little or no additional pain, often not even unpleasant sensation, as the surgeon beams an intense beam of light to "burn" an escape channel for aqueous fluid, usually in the upper edge of the iris.
The Nd:YAG (neodymium:yttrium aluminum garnet crystal) laser has emerged with several advantages over the earlier argon laser, including lower energy requirement, fewer pulses, reduced obstruction, and a lower rate of subsequent closure of incisions. Its portability allows the YAG laser to serve even remote Inuit villages in Alaska previously inaccessible for sophisticated optical surgery.
No wonder that laser surgery in just 25 years has largely displaced traditional scalpel surgery, which involves hospital stays and higher risks. Its low risk allows use earlier in the course of the disease, when its potential benefit is greater.
On the Horizon
Diligence in countering early the subtle onset of glaucoma is the best protection. Research is making such diligence easier.
Ongoing research aims to simplify dosage demands while reducing side effects. For instance, the nuisance of taking preventive eye medications several times a day discourages some people from protecting themselves fully. Work is under way to perfect a once-a-week eye preparation and one-a-day eye drops to ease the use of topical eye medications. Already, dispenser tips that measure more consistent doses of eye drops are improving their use.
Even the standard course of escalating treatment for common glaucoma is being reconsidered. The practice more common in Europe suggests that reversing this order by starting with surgery may be promising. In August 1993, the National Eye Institute announced the Collaborative Initial Glaucoma Treatment Study to compare the long-term effect of treating newly diagnosed primary open-angle glaucoma with standard treatment versus immediate laser surgery.
S.J. Ackerman is a writer in Washington, D.C.
The academy's guidelines include comparing the diameter of the eye's cup to that of its disc to obtain a physical gauge of the likelihood of glaucoma. Estimates are made vertically along an imaginary line drawn through the center of the disc from the 12 o'clock to the 6 o'clock position. The normal optic nerve illustrated with a small cup has a cup-to-disc ratio of less than 0.5, indicating a low probability of glaucoma. Moderately advanced cupping, with a cup-to-disc ratio of 0.6 to 0.8 and a neural rim starting to thin, increases the suspicion of glaucoma. Almost total cup-to-disc ratio of 0.9, exhibiting a very thin neural rim, creates a high level of glaucoma suspicion.
Personal history factors also enter the assessment; these are shown in both table format and in chart form (for browsers that do not support tables). Other variables in risk assessment include extreme nearsightedness or farsightedness, high blood pressure, and steroid use.
People at risk of glaucoma should faithfully have eye checkups at the intervals recommended by their ophthalmologists. Everyone over 40 should have a full eye examination every two years, regardless of risk factors; African Americans should be vigilant after age 30. Adult relatives of persons diagnosed with glaucoma should have regular eye checkups. Glaucoma seems to be hereditary, and even cousins may be at risk if you are.
Glaucoma treatment decisions are personalized. Even eye color may affect the rate at which a person absorbs eye medications.