Glaucoma is a potentially blinding disease that typically causes too much pressure in the eyeball. There are no early symptoms, but if detected early, glaucoma can be controlled. Glaucoma is the second leading cause of blindness in the world, according to the World Health Organization.
In a person with most types of glaucoma, normal fluid pressure inside the eyes (also called intraocular pressure) slowly rises as a result of the fluid aqueous humor not being able to drain properly in and out of the eye. Instead, the fluid collects and causes pressure damage to the optic nerve, and in rare cases, loss of vision.
Physicians used to think that high intraocular pressure was the main cause of optic nerve damage in glaucoma, but we now know that even people with normal intraocular pressure can experience vision loss from glaucoma. This type of glaucoma is called low-tension or normal-tension glaucoma.
Blindness from glaucoma is rare. If blindness does occur, it’s usually because the glaucoma is already advanced when it is first diagnosed, the eye pressure has not responded well to treatment, or patients have not used their prescription eye drops regularly.
Types of glaucoma
Open-angle glaucoma is the most common. In this type, the fluid that normally flows through the pupil into the anterior chamber of the eye cannot get through the filtration area to the drainage canals, causing pressure buildup in the eye. Nearly three million Americans – half of whom do not know they have the disease – are affected by open-angle glaucoma each year.
Low-tension or normal-tension glaucoma
Normal intraocular pressure ranges from 12 mm Hg to 21 mm Hg, but a person may have glaucoma even if their pressure is within this range. Low-tension or normal-tension glaucoma causes optic nerve damage and narrowed side vision.
With this type of glaucoma, the fluid at the front of the eye cannot reach the angle (the area of the eye where the cornea and iris join) and leave the eye because the angle is blocked by part of the iris (the colored part of the eye). This results in a sudden increase in pressure and is generally a medical emergency, requiring immediate treatment to improve the flow of fluid. In the United States, fewer than 10 percent of glaucoma cases are of this type.
Childhood glaucoma is a rare form that often develops in infancy, early childhood or adolescence. Prompt medical treatment is important in preventing blindness.
This type of childhood glaucoma occurs in children born with defects in the angle of the eye that slow the normal drainage of fluid. Prompt medical treatment is important in preventing blindness.
Secondary glaucoma develops as a complication of another medical condition or injury. In rare cases, secondary glaucoma is a complication following another type of eye surgery.
Risk factors for glaucoma
Although anyone can develop glaucoma, some people are at higher risk than others. The following are some common risk factors for glaucoma:
- Age – People over age 60 are at greater risk for developing glaucoma.
- Family history – People with a family history of glaucoma are more likely to develop the disease.
- High intraocular pressure – People with an elevated (greater than 21 mm Hg) intraocular pressure are at an increased risk.
- Medical conditions – Diabetes increases the risk for developing glaucoma. Diabetes can damage blood vessels in the eye, causing a greater risk in developing an increased intraocular pressure. A history of hypertension (high blood pressure), heart disease or hypothyroidism also can increase the risk for developing glaucoma.
- Medications – Inhaled steroids such as beclomethasone (Beclovent), fluticosone (Flovent) and budesonide (Pulmicort) may increase the risk for developing glaucoma.
- Race – According to the National Eye Health Education Program, higher-risk populations include African Americans older than 40 and Mexican Americans older than 60. Glaucoma is the leading cause of blindness for African-Americans.
The National Eye Institute, part of the National Institutes of Health, recommends that anyone in these risk groups receive an eye examination with dilated pupils every two years.