Low Vision Exam
Low vision is a partial loss of sight (also referred to as partially sighted or visually impaired). It is often a loss of visual acuity or sharpness, but may also be a loss of side vision or extreme difficulty with light or glare. Low vision exists when functional vision cannot be adequately corrected with eyeglasses, contact lenses, medications or surgery.
Legal blindness is a level of visual impairment that has been defined by law to determine eligibility for benefits.
The term Legally Blind identifies an individual whose central visual acuity is 20/125 or poorer in the eye with better vision when wearing best correction.
Legally Blind also applies to those individuals that may see better than 20/125 but have a limitation of their peripheral vision. Limitation of peripheral vision may be defined as a visual field diameter of 20 degrees or less in the eye with the larger visual field or a mean deviation of -22dB or greater in the eye with the better visual field.
The Four Most Common Causes of Vision Loss
Age-Related Macular Degeneration (AMD) is the leading cause of irreversible central vision loss in Caucasians over the age of 50 in the U.S. The incidence and progression of all the features of AMD is known to increase significantly with age. It results from damage to the macula, which is the central part of the retina responsible for central vision and ability to see detail. Although the extent of central vision loss can be significant, macular degeneration alone does not cause total blindness.
Glaucoma in its most common form is the second leading cause of blindness in the United States, and the leading cause of blindness among African-Americans. Glaucoma is a disease where pressure within the eye is so high that it can damage the optic nerve and lead to vision loss. It affects side vision long before central vision is affected. Although glaucoma cannot yet be prevented, it can usually be controlled or stopped with treatment and medication.
Diabetic Retinopathy is a complication of diabetes caused by damage to blood vessels in the retina. It is one of the four leading causes of severe vision impairment in older Americans. The risk of developing diabetic retinopathy is greater the longer someone has diabetes. According to the American Academy of Ophthalmology, about 80 percent of people who have had diabetes for at least 15 years have some damage to the retina.
Cataract is a clouding of the lens of the eye, which is normally clear. Light can no longer pass through the lens easily, and vision becomes hazy or blurred. The current treatment, which is safe and highly successful, is surgical removal of the lens which is usually replaced with an intraocular man-made lens.
Projected Estimates of Vision Impairment
According to Prevent Blindness America, twice as many people will be blind in 2030 as there are today (Prevent Blindness America, 1998-2000). The following projections are based on estimates of self-reported vision impairment from The Lighthouse National Survey on Vision Loss (The Lighthouse Inc., 1995) and applied to U.S. Census population projections.
- 9% of persons age 45 and older report a severe vision impairment, representing 8.7 million persons. By the year 2010, when all baby boomers are age 45 and older, this number will increase to 10.7 million.
- About 7.3 million, or 21% of persons age 65 and over, report some form of vision impairment. As baby boomers age, this number will reach 8.3 million in the year 2010; 11.3 million in 2020; and in 2030, 14.8 million persons age 65 and older will report some form of vision loss.
- About 3.8 million, or 11% of persons age 65 and over, report a severe vision impairment. As baby boomers age, this number will reach 4.3 million in the year 2010; 5.9 million in 2020; and in 2030, 7.7 million persons age 65 and older will report a severe vision impairment.
What kinds of devices are available to individuals with low vision to better-enable them to conduct their activities of daily living?
Magnification can be provided in strong reading glasses which require a very close reading distance. There are a variety of lighted and unlighted handheld magnifiers which are particularly good for reading.
There are many electronic devices that use a camera and television in combination with zoom features which allow the patient to magnify text or distance objects.
There are also numerous telescopic devices for distance magnification. Tennessee is one of several states which allow drivers to where a small telescope mounted in the upper portion of the eyeglasses for driving. These bioptic telescopes are prescribed in particular driving situations where patients are very close to legal limits and functional capabilities, but need an occasional boost in vision.
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