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Glaucoma is a group of eye diseases that ultimately result in damage to the optic nerve. It can be present in one or both eyes. The optic nerve is critical to sight because because it transmits visual information from the retina to the brain.
Millions of nerve fibers run from your retina to the optic nerve. These fibers meet at the optic disc.
Inside the eye, a watery fluid is continually produced. This fluid helps to maintain the shape as well as the pressure of the eyeball. The pressure within the eye is called intraocular pressure or IOP. It is the result of the equilibrium between the fluid produced and output from the eye's drainage system. Your IOP can vary at different times of the day, but it normally stays within a range that the eye can handle. In some people, the fluid pressure within the eye is too high. This can lead to damage and death of the sensitive nerve fibers. As they dies, the optic nerve is pushed into a cuppe or curved shape. If the pressure remains too high for too long, the extra pressure may result in vision loss.
Elevated IOP is clearly a risk factor for glaucoma, but we now know that even people with "normal" levels of pressure can experience vision loss from glaucoma. Other factors such as disturbances of blood flow in the optic nerve head as well as intraocular chemicals may interact with IOP to affect the optic nerve. In about one third of cases, there is statistically "normal" IOP. There is no set threshold for intraocular pressure that causes glaucoma. One person may develop nerve damage at a relatively low pressure, while another person may have high eye pressures for years and yet never experience the same level of damage.
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In the early stages of the disease, there may be no symptoms. Vision stays normal, and there is no pain. It is estimated that 67 million individuals worldwide have glaucoma. More than 50 percent of individuals with glaucoma are undiagnosed and diagnosis can be difficult even with a routine eye exam. As the disease progresses, a person with glaucoma may notice his or her side vision gradually failing. If glaucoma remains intreated, a person will slowly lose peripheral vision. They seem to be looking through a tunnel. Over time, straight-ahead vision may decrease until no vision remains.
Glaucomas are classified according to onset (childhood vs. adult), etiology (primary vs. secondary) and underlying mechanism (open vs. closed angle).
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