Glaucoma is a disease that causes loss of peripheral vision due to damage to the retina and optic nerve. Severe glaucoma results in what is called "tunnel vision" because the remaining visual field is like looking through a tunnel. Different types of glaucoma have different causes including: increased or decreased eye pressure, sudden fluid blockage, congenital defects and complications from injury or infection.
Increased or Decreased Eye Pressure Can Cause Glaucoma
Increased eye pressure is caused when fluid reaches the angle where the cornea and iris meet and drains too slowly, causing fluid buildup to the point that the optic nerve is damaged. Increased eye pressure doesn't necessarily mean the person has glaucoma; there must be nerve damage that causes vision loss. Pressure may cause the eyeball to tear loose from the optic nerve. Although high blood pressure is most frequently associated with causing glaucoma, the disease can occur when the person has low or normal eye pressure. In fact, having low blood pressure may be a risk factor.
Sudden Blockage
Sudden blockage at the angle where the iris meets the cornea prevents fluid from draining. The patient experiences severe pain caused by an increase in eye pressure. The patient requires immediate treatment such as medications or laser surgery to avoid complications that can cause blindness.
Congenital Eye Defects
Children may be born with eye defects that cause drainage to be slowed. These defects are usually genetic and inherited. Symptoms that should alert parents and doctors to consider defects that may cause glaucoma include cloudy corneas, sensitivity to light, eyelid spasms 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).
Trauma or Infections
Glaucoma may be caused by complications of other ocular or systemic diseases or trauma. This type of glaucoma is called secondary glaucoma. Secondary glaucoma may be caused by an infection such as uveitis (inflammation of the middle layer of the eye), eye injuries, advanced cataracts, surgical procedures or prolonged use of corticosteroid (used to treat eye inflammations). A severe form of secondary glaucoma--called neovascular glaucoma--is linked to diabetes and may be referred to as diabetic hemorrhagic glaucoma.
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.
