According to the American Academy of Ophthalmology, more than 90 percent of adult glaucoma patients have chronic open angle glaucoma . This type of glaucoma develops gradually, as the drainage portion of the eye becomes less efficient. Often symptomless, it is usually detected during routine eye examinations. Acute closed angle glaucoma , which occurs less frequently, is an emergency condition that develops suddenly and is usually characterized by blurred vision, severe eye pain, headache, rainbow haloes around lights, and nausea and vomiting. Secondary glaucoma occurs because of something else that happened to the eye, e.g., injury, inflammation, or disease.
Congenital glaucoma is present at birth.
In addition to these four basic types of glaucoma there is also a rare condition known as low tension glaucoma , where sustained, abnormally low eye pressure causes vision loss. According to the National Society to Prevent Blindness, of the nearly two million Americans over the age of 40 who have glaucoma, more than 500,000 are African-Americans. In addition, glaucoma can develop at an earlier age among African-Americans and be more difficult to treat. Apart from African ancestry, other risk factors include a family history of glaucoma or diabetes, advancing age, extreme nearsightedness, past eye injuries, diabetes, and taking steroid medications for a long time. The most important action anyone at risk can take is to have regular, comprehensive eye examinations.