GLAUCOMA — THE SNEAK THIEF OF SIGHT

Glaucoma (pronounced glaw-KOH-muh) has been called “the sneak thief of sight,” because the condition comes on gradually before the victim is aware anything is wrong. Glaucoma refers to a group of diseases that elevate eye pressure, damage the optic nerve (carries images we see to the brain), cause visual field loss (side vision, then front vision); and if not caught, can cause blindness. The disease can usually be controlled through early detection and regular dilated eye examinations and treatment by an eye care professional.

Types of Glaucoma

Open-angle glaucoma and closed-angle glaucoma are the two primary and most common types of glaucoma. Open-angle is so-called because the angle between the iris and the cornea is normal but the drainage holes get clogged from the inside; in closed-angle glaucoma the angle is narrower than normal. If fluid can’t flow easily through the opening in the pupil, the iris pushes forward and blocks the drainage holes (see Diagram to the right).

Other types of glaucoma can be linked to genetics, injuries or inflammation of the eye, eye diseases (i.e., cataracts or eye tumors) or other health conditions (i.e., advanced diabetes).

This article will primarily address the open-angle glaucoma, the most common type, but it will touch briefly on closed-angle glaucoma.

Causes of Open-Angle Glaucoma

Most people are aware that glaucoma has something to do with the pressure inside the eye. This pressure is called intraocular pressure (IOP). For clarification, please look at the front of the eye in the diagram below, followed by an explanation given by the National Eye Institute (NEI):

“At the front of the eye, there is a small space called the anterior chamber. Clear fluid flows in and out of the chamber to bathe and nourish nearby tissues. In glaucoma, for still unknown reasons, the fluid drains too slowly out of the eye. As the fluid builds up, the pressure inside the eye rises. Unless this pressure is controlled, it may cause damage to the optic nerve and other parts of the eye and loss of vision.”

If the IOP is found to be high with known optic nerve damage, it is considered glaucoma; if the IOP is high with no optic nerve damage, it is considered ocular hypertension or glaucoma-suspect. In all cases, a close watch is needed through dilated eye exams.

There are usually no symptoms in open-angle glaucoma until vision is impaired. Blind spots and vision changes develop as the optic nerve deteriorates — first, the peripheral vision (side vision) is affected; second, the central vision (front vision), and if not treated, blindness can occur. Other noticeable changes or symptoms could include the inability to adjust the eyes to darkened rooms, mild and chronic headaches, or frequent changes of eyeglasses that do not correct vision.

Closed-angle glaucoma is less common and occurs as the lens of the eye gradually becomes larger, resulting in part of the iris obstructing the angle causing it to close. This blocks the aqueous humor from reaching the drainage system. This condition is usually acute and occurs suddenly and painfully and requires emergency medical attention. Individuals may experience severe eye or facial pain, loss of vision or blurred vision, headaches, red eyes, haloes appearing around lights, nausea and vomiting. Closed-angle glaucoma can also be chronic, developing gradually over time.

Risk Factors

Today, nearly three million people have glaucoma. Before a complete diagnosis for glaucoma is determined, the American Academy of Ophthalmology (AAO) mentions that there are important risk factors to be taken into account, such as

And, recently, scientists have recognized other possible risk factors, such as exfoliation syndrome (buildup of whitish material on the lens of the eye) and poor blood flow to the optic nerve, which could be caused by low blood pressure.

Tests and Treatments

Studies has shown that the risk of blindness from glaucoma can be reduced by early detection and treatment through a dilated eye examination at least once every two years. For conclusive findings your eye doctor may suggest some of the following tests include intraocular pressure measurement (tonometry); optic nerve damage evaluation (ophthalmoscopy); drainage angle of the eye (gonioscopy), near and far vision measurement (visual acuity); visual field measurement (perimetry); and the most recent diagnostic tool, the nerve fiber layer measurement (GDx Nerve Fiber Analyzer).

Available treatments used today do not cure the disease, but lowering the pressure within the eye is believed to slow the progression of the disease. Open-angle glaucoma treatments include medications, laser surgery and operative surgery. In its early stages, glaucoma is usually treated with daily eye drops or pills, or both. Some drugs are designed to reduce pressure by slowing the flow of fluid into the eye; others help to improve fluid drainage. You may want to talk with your eye care professional about the proper treatment for you and any side effects that could occur. Be sure that your eye care and health care professionals have a list of all your medications, over-the-counter drugs and supplements.

In some patients with open-angle glaucoma the beneficial effect of the eye drops wears off with time and laser surgery (trabeculoplasty) is recommended to enlarge the drain to help control eye pressure; in closed angle or acute glaucoma, laser surgery (iridotomy) may be needed to improve the flow of aqueous fluid to the drain. In some cases, laser surgery may be used even before medications are tried.

In some cases, operative surgery (trabeculectomy) is required to create a new drainage channel for the fluid to leave the eye; hence, lowering the pressure.  Recently, another treatment, known as endoscopic laser surgery, is being performed on persons with severe glaucoma damage that has not responded to standard glaucoma treatment. The long-term effects of this surgery are still being evaluated.

Research

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Glaucoma research has come a long way from thinking that it is simply a condition caused by increased pressure within the eye. Recognizing risk factors, including hereditary and genetic makeup, is changing the conception of what glaucoma is and what causes it.

Numerous laboratory and clinical studies are being conducted across the country. Here are just a few of the topics being researched: gene therapy, diagnostic techniques; medications; aqueous humor inflow and outflow; tissue changes in the optic nerve; surgical procedures; surgical wound healing; role of nutrition through food and supplements —vitamins, minerals and herbs (Sources: National Eye Institute; American Academy of Ophthalmology; “Understanding Glaucoma,” Krames Communications). 

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The Visionary, published as a service of the Illinois Society for the Prevention of Blindness,
is available upon request. The information contained in this issue,
taken from sources considered to be accurate,
does not replace the need for professional eye care consultations and treatments.

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