Glaucoma

Glaucoma is one of the four leading causes of blindness throughout the world. The others are macular degeneration, diabetes and cataract. Glaucoma is a disease that is limited to the eye. It is associated with an increase in the pressure within the eye that results in damage to the optic nerve. This nerve carries visual images to the brain.

Some of the normal structures within the eye (cornea and lens) are devoid of blood vessels. The visual field is an important test both in the diagnosis of glaucoma and also for following any progression. This fluid is produced behind the iris, circulates into the anterior chamber of the eye and is drained out by a small canal, which has multiple sieve-like openings throughout the circumference of the eye. The fluid then re-enters the general circulation. In glaucoma there is an impediment to this drainage and pressure builds up. Strangely, and despite extensive research, we still do not know exactly what causes the obstruction to outflow.

The normal pressure within the eye is a range of 10-22 mm Hg (millimeters of mercury). We determine this indirectly by measuring the force necessary to flatten a very small area of the cornea with a gauge called a tonometer. However, pressure is only one factor in glaucoma. Some patients develop glaucoma with a pressure lower than 22mm and others do not with a pressure over 22mm. There are several types of glaucoma. A shortened classification is:

Open Angle
Narrow Angle
Congenital (present at birth)
Juvenile
Secondary (associated with other diseases)

While glaucoma may develop at any age, the incidence increases with increasing age. Those over 60 years of age are 6 times as likely to develop glaucoma as those under 60. Heredity is one risk factor as is the prolonged use of steroid medication.

The word angle refers to the anatomic area where the iris meets the clear cornea on the inside of the eye. This is where the small drainage canal is located. Open and narrow angle are the most common types of glaucoma and further discussion will be limited to these entities.

Open Angle Glaucoma

This is the most common type in the United States and accounts for about 85% of glaucoma cases. There are no symptoms until late in the disease. It is usually discovered on a routine examination. It is more common in women than men and the incidence is significantly greater (and harder to treat) in African Americans. It is a chronic disease with gradual progression over years if untreated.

The diagnosis is made by the finding of an increased pressure, the appearance of the optic nerve head in the back of the eye and changes in the peripheral visual field. The visual field is an important test both in the diagnosis of glaucoma and also in following any progression. The visual field is a computerized test that presents the eye with multiple lights in various areas of the peripheral field. Characteristic pattern defects in the vision of glaucoma patients indicated damage to the nerve fibers.

There are multiple options for the treatment of chronic open angle glaucoma. These include many different kinds of eye drops, some of which increase the outflow of fluid from the eye and others which decrease the production of fluid. Both will decrease the pressure within the eye. However, all of these medications have varying side affects and each patient must be evaluated individually as to which medication is best.

Surgical procedures also are used to control the pressure including laser and the creation of artificial draining channels.

Narrow Angle Glaucoma

This type of glaucoma is entirely different. The classic presentation is acute, painful with blurred vision and often nausea and vomiting (due to the pain). Narrow angle glaucoma results from a sudden occlusion of the angle, blocking the entire circumference of the drainage channels. Pressures within the eye often measure 50-80 mm of Hg. Narrow angle glaucoma is an ocular emergency. If the pressure is not brought under control within 48 hours, adhesions between the iris and cornea may permanently obstruct the outflow channels. Patients who are farsighted are at increased risk because of a shorter eyeball with resulting crowding of the angle.

Treatment consists of reducing the pressure with many of those agents used to treat open angle glaucoma then performing a laser iridotomy (hole in the iris) to allow fluid another avenue to pass into the drainage channel area. Often a preventive laser is preformed in the other eye first while pressure in the affected eye is being reduced. If treated early, chances are good that the pressure will be controlled, sometimes without medication.

Sometimes the glaucoma is the result of both an open and narrow angle mechanism.