Glaucoma causes loss of peripheral vision due to damage to the retina and optic nerve. Risk factors include being over 60 years of age, having a family history of glaucoma and being of African American decent. The most common type of glaucoma, called open-angle, is caused by increased eye pressure when fluid drains too slowly. Other types of glaucoma include closed-angle, congenital and secondary glaucoma. Symptoms greatly vary depending on the type of glaucoma.
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Open-Angle Glaucoma
During the early stage of open-angle glaucoma there are no symptoms and vision appears normal. As peripheral vision gradually deteriorates the person will have greater difficulty scanning the environment and may bump into objects located at his sides or trip over obstacle located in his missing lower visual field. The peripheral visual field serves as a warning system, enabling the person to pick up quick movement such as a child running into the street even while using central vision to look straight ahead. The cells that sense peripheral vision also function better in dim light than do the cells used for central vision. Therefore, the person with glaucoma will experience more severe disability at night while functioning without the peripheral field's warning system. Left untreated, further progression of glaucoma causes tunnel vision because the remaining visual field is like looking through a tunnel. Ultimately, central vision may totally disappear, causing blindness.
Closed-Angle Glaucoma
People with closed-angle glaucoma will have sudden increase in eye pressure, causing intense pain, nausea, eye redness, halos around lights and blurred vision. This is caused by blockage where the iris meets the cornea. The iris is the membrane that covers the eye and controls how much light enters the retina. The cornea is the transparent cover over the iris. Without immediate treatment for the blockage, the person can become blind within one or two days.
Congenital glaucoma
Children may be born with defects that slow down drainage in the eye, causing blockage. Symptoms are obvious and may include cloudy eyes, light sensitivity and excessive tearing. Congenital glaucoma is associated with abnormalities such as aniridia (absence of the iris) and Marfan's syndrome (a genetic disorder of connective tissue). Congenital glaucoma typically occurs more often in boys than in girls.
Secondary Glaucoma
Glaucoma may be caused by complications from eye injuries such as a corneal abrasion that cause severe sensitivity to light or other injuries that present with symptoms of redness, pain and/or swelling. Other secondary causes of glaucoma include eye infections such as uveitis (inflammation of the middle layer of the eye). Eye infections can be differentiated from allergies because the allergies will always affect both eyes; whereas, an infection generally affects only one eye. Symptoms of eye infections include redness, pain, discharge and light sensitivity. Secondary glaucoma can also be caused by cataracts or tumors. Cataract symptoms include a cloudy lens and blurry vision. An eye tumor may present with symptoms of pain, swelling and loss of vision.
References
- "Coping with Vision Loss"; Bill Chapman; 2001.
- "Low Vision Rehabilitation"; Mitchell Scheiman; 2007.
- "Foundations of Low Vision"; Anne L. Corn and Alan J. Koenig; 2004.
