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Common Visual Impairments
March 20, 2008
Visual impairment is a term used by researchers that refers to a "functional loss of vision" (National Dissemination Center for Children with Disabilities (NICHCY), 2003). Prevent Blindness America defines visual impairment as vision of 20/40 or less in the better eye with corrective lenses or a visual field of less than 20 degrees diameter.
- Glaucoma is a disease of the eye that is caused by a gradual degeneration of cells in the optic nerve. The loss of these cells leads to a gradual narrowing of the field of vision beginning at the periphery. There is no known cause for the most common form of glaucoma, but it is commonly believed to be associated with the inability of fluid to drain from the eyes causing an increased intraocular pressure. Onset generally occurs later in life and people over 60 are six times more likely to get glaucoma than the younger population. While there is no way to prevent glaucoma, it can be successfully treated if diagnosed early.
- Age-related macular degeneration (MD) is caused by the malfunction of photosensitive cells in the macula which results in a loss of the central field of vision. Additional symptoms may include a distortion of images especially at the center of the visual field; a darkened area in the center of an image; and diminished color perception. The peripheral vision of people with macular degeneration is unaffected. Laser therapy is often used as a treatment in some MD, but this intervention does not guarantee that vision will be saved.
- Optic nerve atrophy (ONA) is caused by tissue damage in the optic nerve resulting in either partial or profound loss of vision. The causes of ONA vary widely. In adults, ONA can be caused by trauma, toxic substances, radiation, and shock. Disease related causes include multiple sclerosis, brain tumor, or stroke. In children, ONA is commonly caused by anoxia, tumors, hydrocephalus, heredity, and rare degenerative disorders. Optic nerve atrophy reduces central vision acuity resulting in an inability to see detail. It also reduces the field of vision, causing images in the periphery to be lost. Once vision is lost through ONA, it cannot be recovered.
- Diabetic Retinopathy is a visual disorder associated with diabetes that causes retinal blood vessels to leak into the retina causing macular edema. Vision loss from diabetic retinopathy generally worsens over time. It will begin with a blurring of the vision and as it develops will cause development of cloudy vision, blind spots, or floaters. Careful control of diabetes and regular eye exams can delay the development of the disorder.
- Retinitis Pigmentosa (RP) is a progressive disorder that results from the degeneration of photoreceptor cells of the retina. As these cells degenerate, gradual vision loss occurs. The disease often first occurs in adolescence and continues to progress as the individual ages often resulting in blindness in young adults. RP is a genetic disorder that is linked to more than 70 different genetic defects.
- Cataracts result from a clouding of the lens of the eye. Symptoms of cataract include blurred vision, light sensitivity, double vision, and an apparent fading or yellowing of colors. While the most common cataracts are age-related, other types of cataracts include: secondary cataracts - resulting from diseases; traumatic cataracts - resulting from injury to the eye; cataracts resulting from exposure to radiation. In the United States, cataract surgery is an outpatient procedure that replaces the damaged lens of the eye with an intraocular lens.
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Resources and Additional Information
American Foundation for the Blind: www.afb.org
National Eye Institute: www.nei.nih.gov