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Glaucoma-A Silent Thief

Cover Story

Issue: December 2009

By: Stacy Schwan

It is a silent thief, slowly stealing precious sight from millions of unsuspecting people worldwide. Of more than 2.2 million Americans over age 40 who have glaucoma, about half never learn about it until it is too late. By then the damage has been done—they’ve been robbed blind.

Have you had your eye exam this year? And have you been screened for glaucoma? These are questions that general physicians should routinely ask every patient, says Julie A. Chen, M.D., ophthalmologist and glaucoma specialist with Solano Regional Medical Group in Fairfield.

Because the most common types of glaucoma are asymptomatic until the optic nerve has been irreparably damaged, it is important to be screened regularly, particularly for those in high risk categories. “We’re trying to increase awareness among patients and also among primary care providers and other eye care professionals that glaucoma screening is something that should be placed up there with prostate cancer screening and breast cancer screening, something they think about in their routine evaluation of patients,” Dr. Chen says.

A neurodegenerative disorder

“Glaucoma can be thought of as a neurodegenerative disorder, much like Alzheimer's or Parkinson's,” says Dr. Chen. “Glaucoma is a group of diseases that causes damage to the optic nerve. It is normal for the optic nerve to age over time, but what distinguishes glaucoma is that this aging process is abnormally accelerated.”

The two most common types of glaucoma are open angle glaucoma, affecting about 95% of glaucoma patients, and angle closure glaucoma. “In the case of open angle glaucoma, the eye’s drainage system becomes clogged over time, ultimately resulting in damage to the optic nerve,” says Dr. Chen. “In this type of glaucoma, patients have no symptoms and no early warning signs, which is why screening exams and early detection are the keys to preventing vision loss.”

Angle closure glaucoma is much rarer and is usually acute, but it may also be silent and chronic. In acute angle closure glaucoma the normal flow of eye fluid (aqueous humor) becomes suddenly blocked. Symptoms may include severe eye pain, blurred vision, nausea and vomiting, and colored halos around lights. Acute angle closure glaucoma constitutes an emergency and must be treated immediately or blindness could result in one or two days.

A third type of glaucoma is congenital glaucoma, “which is much more uncommon but much more devastating,” says Dr. Chen. “A baby born with glaucoma often presents with tearing, an enlarged appearing eye, and light sensitivity. That type of glaucoma is much more difficult to treat, but luckily it’s much more rare.”

A misunderstood disease

Glaucoma is a very misunderstood disease, says Dr. Chen. “It was once thought that high pressure inside the eye—intraocular pressure—was the main cause of the optic nerve damage. So many people equated glaucoma with high eye pressure, and that is simply not the case. As glaucoma specialists, we often see patients with very advanced glaucoma who were told in the past that they did not have glaucoma just because their eye pressure was normal. High eye pressure is one leading risk factor for glaucoma, but many patients with glaucoma have normal or even low eye pressures.”

In fact, according to some researchers, it is possible that fluctuations in intraocular pressure are just as damaging as high intraocular pressures. “One of the challenges in treating and diagnosing glaucoma is that there is no way to monitor a patient's pressure continuously throughout the course of the day, and there's no simple at-home eye pressure measurement device like the blood pressure cuffs many patients use to monitor hypertension,” says Dr. Chen. “We generally see glaucoma patients every 3 to 4 months, therefore, we don't really know what the eye pressure is at any other time of during that period. Some studies have shown that in some patients, the eye pressure is highest at nighttime while the patient as asleep, and we have no way of measuring that currently.”

A lot of patients also wonder about the correlation between eye pressure and blood pressure, Dr. Chen notes. “High blood pressure and high eye pressure are not really correlated in any predictable fashion. In fact, in some cases, over-treatment of hypertension or a low blood pressure can be a risk factor for glaucoma because this affects the ocular perfusion pressure. Put simply, ocular perfusion pressure is the difference between the blood pressure in the body and the pressure in the eye. If the blood pressure in the body is too low, and the intraocular pressure is high, this results in low ocular perfusion pressure and the optic nerve may not receive an adequate blood supply.”

Another misconception about glaucoma is that if you have excellent vision, you cannot have glaucoma. In fact, there are no real symptoms for open angle glaucoma, and that’s why it’s so dangerous, Dr. Chen says. “Glaucoma steals sight without any warning or without any symptoms, and it affects your peripheral vision first. So you wouldn’t notice a change in your vision until it creeps into your central vision, and by that time, the glaucoma is already very advanced and you’ve probably already lost over 90% of your vision.”

Risk factors

Major risk factors for glaucoma include age, heredity and ethnicity. People age 60 and over are at most at risk, age 40 and over for African Americans. “I like to tell my patients that if everyone lived to be 200, everyone would develop glaucoma,” says Dr. Chen. “But you’re much more likely to develop it if you’re over 60.”

Family history increases the risk for all types of glaucoma of up to five times over someone with no family history.

Ethnicity is another important risk factor for glaucoma. Studies show that African Americans are five times as likely to develop glaucoma as Caucasians. The risk is also higher for Hispanics and Native Americans, and East Asians have a slightly higher risk for angle closure glaucoma.

Certain risk factors—such as high eye pressure, a thin cornea, and abnormal optic nerve anatomy—can only be measured through a comprehensive, dilated eye exam.

“Some other risk factors are steroid use, which includes steroid inhalers to control asthma; eye injuries or trauma to the eye; diabetes; nearsightedness; or prior surgeries,” says Dr. Chen.

Importance of glaucoma screening exams

A lot of patients just have their glasses checked every year and assume that they are being adequately screened for glaucoma and other eye diseases, which may not always be the case. “Unfortunately, once damage from glaucoma occurs it cannot be reversed, even with surgery,” says Dr. Chen. “The official recommendation by the Academy of Ophthalmology and by the American Glaucoma Society is that anyone with risk factors for glaucoma, or anyone over the age of 40 even with no risk factors, should get a thorough screening exam with an ophthalmologist.

“The challenge is, just measuring the eye pressure is not an adequate screening test for glaucoma,” Dr. Chen adds. “You should really have an optic nerve evaluation. There’s a huge group of patients that have what we call normal tension glaucoma, particularly Japanese patients. Almost all Japanese patients with glaucoma do not have high eye pressures. Refractive surgery—that is lasik surgery—has also become popular, and it thins the cornea. Once you’ve had that surgery, your eye pressure measure is artificially low, so patients that have had the procedure almost never would present with a high pressure, even if they did have glaucoma.”

Confusion over coverage

Dr. Chen admits that health insurance for eye care can be confusing, even for a healthcare provider. “There’s medical insurance, which covers examinations for eye disease and would cover a glaucoma screening exam. A lot of patients also have separate vision plans, which covers refractions, glasses, and also covers screening eye exams. Some patients don’t realize that they have the option to both see an optometrist through their vision plan and also see an ophthalmologist through their medical insurance.”

Once again, she stresses, the most important thing is to obtain a thorough baseline screening and then proper follow up screenings at intervals thereafter.

“It’s always very tragic when we see someone who comes into the clinic in the very late stages of glaucoma and we feel like had they come in 10 years earlier we could have really made a difference,” Dr. Chen says.

Treatment options

Treatment options are changing all the time, says Dr. Chen. “The primary treatment is usually topical eye medications, and those are constantly being developed. There is a lot of glaucoma research directed toward trying to develop neuroprotective drugs to treat glaucoma, much like the drugs for Alzheimer's and Parkinson's.”

Both laser and conventional surgery may be used in addition to medication in an attempt to save what vision remains. New surgical techniques have improved outcomes, however they do not improve sight already lost from glaucoma.

The glaucoma surgeries Dr. Chen performs include trabeculectomy, ExPRESS shunt and Ahmed glaucoma valve implants. “These are all surgeries performed to lower the intraocular pressure of
the eye. In trabeculectomy, a microscopic piece of tissue is removed from the drainage angle of the eye. Essentially, this works like a pressure release valve, creating an alternative channel for the fluid to drain out of the eye. The fluid then collects under the conjunctiva and forms a small bleb. The ExPRESS shunt and Ahmed valve are more recently developed surgeries which also work to lower the intraocular pressure by creating an alternative channel for the intraocular fluid to escape from the eye that may provide a more controlled release mechanism.”

Laser procedures performed by Dr. Chen include peripheral iridotomy, peripheral iridoplasty and selective laser trabeculopasty.

Early intervention is key

Glaucoma is the second most common cause of blindness in the United States and is a disease for which there is no cure. Rather than discouraging Dr. Chen from entering the specialty, these grim facts have challenged and motivated her to attempt to fill an unmet need.

“It’s not as exciting as, maybe, doing refractive laser surgery, but it is something that affects a huge proportion of individuals in the United States. There is a lot of research and development that still needs to be done in the area, and because there is no cure for glaucoma, we’re constantly trying to develop improved treatments and better surgeries so that we can prevent vision loss in more of our patients,” she says.

“That’s why we emphasize seeing an ophthalmologist to have early screening. Because glaucoma it is a treatable condition, and if you intervene early with medications, you can avoid vision loss.”

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