Glaucoma (glah-CO-muh) is an eye disease characterized by higher-than-normal pressure inside your eye. The pressure can increase gradually or suddenly, slightly or dramatically, and it may occur for various reasons, depending on the type of glaucoma. Of all the possible causes of blindness, glaucoma is among the most common, but it's also the easiest to prevent. Chronic glaucoma is of two types: chronic simple glaucoma and chronic secondary glaucoma. About 95 percent of all cases of glaucoma are chronic simple glaucoma. The word simple means that the rise in pressure isn't the result of any known underlying cause. Heredity is apparently one factor, which is why you should be tested before you reach age 40 if you have a family history of glaucoma. People of African ancestry also have the disease in far greater numbers than members of other races, possibly because of the greater amount of pigmentation present in very dark eyes. Chronic secondary glaucoma, which makes up about five percent of glaucoma cases, seems to develop in people whose eyes tend to inefficiently drain aqueous (AH-kwee-us) fluid. It has all the symptoms of chronic simple glaucoma; however, the cause of the defect in drainage is undefinable, although it's usually a complication of another eye problem. Other causes of poor drainage in this type of glaucoma may be an internal eye infection, allergic reaction, trauma, tumor, or scar tissue. Chronic secondary glaucoma can also be a complication of a cataract, when the diseased lens encroaches upon the front of the eyeball, causing the drainage angle to be narrowed or blocked. It can also be a side effect of a medication, such as one of the corticosteroids (cor-ti-koe-STER-oids).