Glaucoma​—The Thief of Sight

FOR a moment, keep your eyes focused on the last word in this sentence. Without moving your eyes, could you see some of the area above, below, and on either side of this magazine? Most likely you could, thanks to what is known as peripheral vision. This ability makes you aware of that suspicious-looking person who is approaching you from the side. It helps you to sidestep objects on the ground and avoid bumping into walls as you walk. And if you drive a car, peripheral vision can alert you that a pedestrian has stepped off the curb.

But even as you read this page, your peripheral vision could slowly be disappearing​—without your even realizing it. Worldwide, an estimated 66 million people are affected by a group of eye diseases collectively known as glaucoma. Of that number, over five million have become totally blind, making glaucoma the third-largest cause of permanent blindness. “Yet even in developed countries with public educational programmes that target glaucoma, half of the individuals with glaucoma remain undiagnosed,” states the medical journal The Lancet.

Who is at risk of developing glaucoma? How is it detected, and how is it treated?

What Is Glaucoma?

First we need to understand a little about our eyes. A brochure produced by the Glaucoma Foundation of Australia explains: “The eye’s rigidity is obtained through pressure​—the soft tissues of the eye are ‘pumped up,’ just like a car tyre or a balloon.” Inside the eye, a pump called the ciliary body moves a fluid known as aqueous humor from the blood vessels into the eye. “The aqueous circulates deep inside the eye, nourishing the living structures of the eye and returns to the blood stream through a strainerlike structure called the trabecular meshwork.”

If this meshwork becomes blocked or constricted for any reason, the pressure inside the eye will increase and eventually begin to damage the delicate nerve fibers at the back of the eye. This condition is called open-angle glaucoma and accounts for about 90 percent of all cases.

The pressure inside your eye, known as intraocular pressure (IOP), can vary from hour to hour and is affected by a variety of factors including your heartbeat, the amount of fluids you drink, and your body position. These natural variations cause no damage to your eye. High pressure in the eye is not by itself proof of glaucoma, since “normal” eye pressure varies from person to person. Still, high IOP is one of the indicators of glaucoma.

A rare form of this disease is called acute, or angle-closure, glaucoma. Unlike open-angle glaucoma, this type involves a sudden increase of pressure in the eye. It causes severe pain in the eye, along with blurred vision and vomiting. If not treated within hours of the onset of symptoms, it will often cause blindness. Another category is called secondary glaucoma. As the name implies, this type is triggered by such other conditions in the eye as tumors, cataracts, or eye injuries. A small group of people are afflicted by the fourth type, known as congenital glaucoma. This type is present at birth or shortly thereafter and is indicated if the infant has enlarged eyeballs and an increased sensitivity to light.

 How It “Steals” Vision

Glaucoma could steal up to 90 percent of your vision in one eye without your being aware of it. How is that possible? All of us have a naturally occurring blind spot at the back of each eye. This spot on the retina, where your nerve fibers join together to form the optic nerve, is devoid of light-sensing cells. You are unaware of this blind spot, however, because your brain has the ability to “paint in” the missing bits of the picture. Ironically, it is the brain’s ability to do this that makes glaucoma so insidious.

Dr. Ivan Goldberg, a leading Australian ophthalmologist, told Awake!: “Glaucoma is called the sneak thief of sight because it doesn’t give you any symptoms. The most common kind of glaucoma is slow and steady and, without any warning, causes damage to the nerve structure that connects the eye to the brain. Whether your eyes water or they don’t, whether they are dry or not, whether they see clearly to read and write or they don’t has nothing to do with glaucoma. You can have perfectly comfortable eyes and have very bad glaucoma.”

Detecting the Thief

Unfortunately, there is no single comprehensive test for glaucoma. Using a device known as a tonometer, an eye specialist may start by checking the fluid pressure in your eyes. The instrument is used gently to flatten the cornea, or front part of your eye. The amount of force required to perform this task  is measured, and in this way the pressure inside your eye can be gauged. The eye specialist may also look for signs of glaucoma by using instruments that identify damaged tissue in the nerve structure that connects the eye to the brain. Dr. Goldberg says: “We see if the nerve fibers or blood vessels at the back of the eye are unusual in shape, because that can be an indication that nerves are being damaged.”

Glaucoma is also detected by visual-field testing. Dr. Goldberg explains: “A person looks into a bowl of white light, and there is a brighter white light that is shone at a little spot inside that bowl. The person responds by pressing a button when he or she can see the little white light.” Failure to recognize the white light when it is at the outer edge of your visual field could indicate glaucoma. New instruments are being developed that might simplify this rather tedious procedure.

Who Is at Risk?

Paul is a healthy man in his early 40’s. He says: “I went to the optometrist to be tested for a new pair of glasses, and during the visit he asked me if I had a family history of glaucoma. I did some investigating and discovered that both an aunt and an uncle had this condition. I was referred to an eye specialist, who confirmed that I had glaucoma.” Dr. Goldberg explains: “If your mother or father has it, your risk of getting glaucoma goes up three to five times. And if you have a brother or a sister with glaucoma, then your risk of getting it goes up between five and seven times.”

Dr. Kevin Greenidge of the Glaucoma Foundation in the United States highlights other risk factors, saying: “If you are over 45 and of African descent, or if you have any of these risk factors​—family history of glaucoma, nearsightedness, diabetes, a previous eye injury or regular use of cortisone/steroid products—​get your eyes tested every year.”  Even if you have no risk factors and are under 45, the foundation recommends that you still have your eyes checked for glaucoma every four years. If you are over 45, you should have this checkup every two years.

Treat It and Beat It

The treatment for Paul’s glaucoma includes the use of special eye drops once a day. Paul says: “The drops I use inhibit the production of the aqueous fluid in the eyeball.” Paul also underwent a treatment in which a laser beam was used to “drill” about ten tiny holes in the front of his eyes near where the natural drain holes occur. He says: “When I had my first eye treated with the laser, I was quite tense and nervous, and this magnified the discomfort that I felt. However, when my second eye was treated a few days later, I knew what to expect. I was far more relaxed, and the doctor had virtually finished the operation before I realized it.” Treatment has helped stabilize the pressure in Paul’s eyes.

Paul’s outlook is thus positive. He says: “My retinas have only been slightly damaged, and thankfully, I still have my full peripheral vision. If I remember to use my eye drops each day, it is likely to stay that way.”

Is the “sneak thief of sight” stealing your vision? If you have never had your eyes checked for glaucoma​—and especially if you are in one of the risk groups—​it would be wise to ask your doctor for a glaucoma examination. As Dr. Goldberg says, “much of the damage from glaucoma can be prevented by timely and appropriate treatment.” Yes, you can thwart this thief of sight!

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Your risk of developing glaucoma increases if

● You are of African descent

● Someone in your family has glaucoma

● You have diabetes

● You are nearsighted

● You are a regular, long-term user of cortisone/steroid​—used in some medical creams and asthma sprays

● You have a previous eye injury

● You are over 45 years of age

[Picture]

Regular testing can prevent serious vision loss

[Diagram/Pictures on page 25]

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OPEN-ANGLE GLAUCOMA

Cornea

Iris

Lens

Retina

Optic disk, or blind spot, is where nerve fibers join to form the optic nerve

Optic nerve carries visual impulses to the brain

Ciliary body, where the fluid is made

1 Aqueous humor is a clear fluid that nourishes the lens, the iris, and the inside of the cornea. It is not the same as tears, which bathe the outside of the eye

2 Trabecular meshwork drains the fluid

3 If the meshwork is blocked or clogged, pressure increases inside the eye

4 If pressure increases, the delicate nerve fibers at the back of the eye get damaged, causing glaucoma or reduced vision

[Pictures on page 25]

Optic disk

What you would see

NORMAL VISION

EARLY GLAUCOMA

ADVANCED GLAUCOMA

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Photos of optic disks: Courtesy Atlas of Ophthalmology