What Is the Medical Definition of Glaucoma?Glaucoma refers to certain eye diseases that affect the optic nerve and cause vision loss. Most, but not all, of these diseases typically produce elevated pressure inside the eye, called intraocular pressure (IOP). Normal IOP is measured in millimeters of mercury and can range from 10-21 mm Hg. An elevated IOP is the most important risk factor for the development of glaucoma.Elevated IOP is sometimes called ocular hypertension. If your doctor diagnoses ocular hypertension, it does not mean you have glaucoma, but it does mean you are at a higher risk for developing the condition, and you should see an ophthalmologist (a medical doctor who specializes in eye care and surgery) frequently.Do You Always Go Blind from Glaucoma?Half of the people with glaucoma are usually unaware of it until a serious loss of vision has occurred. The disease is not curable, but can be managed. Early diagnosis and treatment usually results in excellent success, and vision is saved.Many factors are associated with an increased risk of developing glaucoma, some of which are elevated IOP, a family history, ethnic background, and older age.What Are the Types of Glaucoma?The two main types of glaucoma are angle closure and open angle.In angle-closure glaucoma, the normal drainage canals within the eye are physically blocked. Angle-closure glaucoma can be acute (sudden) or chronic (long-lasting). In acute angle-closure glaucoma, a sudden increase in IOP occurs because of the buildup of fluid known as aqueous humor. Acute angle-closure glaucoma is considered an emergency because optic nerve damage and vision loss can occur within hours of the onset of the problem. Chronic angle-closure glaucoma may cause vision damage without symptoms.In open-angle glaucoma, the drainage system remains open. Open-angle glaucoma also may cause vision damage without symptoms.Normal (or low) tension glaucoma is an unusual and poorly understood form of the disease. In this type of glaucoma, the optic nerve is damaged even though the IOP is consistently within a range usually considered normal.Childhood glaucoma is rare and starts in infancy, childhood, or adolescence. It is similar to open-angle glaucoma, and few, if any, symptoms are present in the early stage. Blindness can result if it is left untreated. Like most types of glaucoma, this childhood form is thought to be inherited.Congenital glaucoma is a type of childhood glaucoma that usually appears soon after birth, although it may be delayed until later in the first year of life. Unlike childhood glaucoma, though, congenital glaucoma often has noticeable signs that may include tearing, light sensitivity, and cloudiness of the cornea. This type of glaucoma is more common in boys and can affect one or both eyes.Secondary glaucoma refers to an increased IOP that is a result of a structural problem within the eye. This secondary type may be the result of injury to the eye or other medical conditions. This form of glaucoma is different because treatment is aimed at treating the underlying cause as well as lowering the increased pressure within the eye. What Does Glaucoma Look Like? Illustration of the eye. Illustration of the eye.