Glaucoma is a group of eye diseases which result in damage to the optic nerve and vision loss. A major risk factor is increased pressure in the eye. The disorders can be roughly divided into two main categories: "open-angle" and "closed-angle" (or "angle closure") glaucoma. Open-angle chronic glaucoma is painless, tends to develop slowly over time and often has no symptoms until the disease has progressed significantly. Closed angle glaucoma is usually chronic and asymptomatic but can present all of a sudden as well. This involves sudden eye pain, blurred vision, mid-dilated pupil, redness, nausea and vomiting, resulting from a sudden spike in intraocular pressure from iridotrabecular contact. Glaucoma can permanently damage vision in the affected eye, first by decreasing peripheral vision (reducing the visual field), and then potentially leading to blindness if left untreated.
The many subtypes of glaucoma can all be considered to be a type of optic neuropathy. The nerve damage involves loss of retinal ganglion cells in a characteristic pattern. Raised intraocular pressure (above 21 mmHg or 2.8 kPa) is the most important and only modifiable risk factor for glaucoma. Some may have high eye pressure for years and never develop damage, a condition known as "ocular hypertension". Conversely, the term 'low tension' or'normal tension' glaucoma is used for those with optic nerve damage and associated visual field loss, but normal or low intraocular pressure. Closed-angle glaucoma also involves damage to the optic nerve, however, is characterized by closure of part of the filtration angle as a result of iris apposition to the trabecular meshwork(iridotrabecular contact).
If the condition is detected early enough, it is possible to arrest the development or slow the progression with medical and surgical means. Open angle chronic glaucoma is treated with either glaucoma medication to lower the pressure, or with various pressure-reducing glaucoma surgeries. Treatment of closed angle glaucoma involves medication to bring the intraocular pressure down and laser surgery to the iris to open the drainage angle and hence reduce the eye pressure.
Glaucoma has been called the "silent thief of sight" because the loss of vision often occurs gradually over a long period, and symptoms only occur when the disease is quite advanced. Worldwide, glaucoma is the second-leading cause of blindness after cataracts. It is also the leading cause of blindness among African Americans. Although the term "glaucoma" has a history relating to disorders of the eye going back to ancient Greece, in English the word was not commonly used until after 1850, when the development of the ophthalmoscope permitted visualization of the optic nerve damage caused by glaucoma