Causes of Vision Impairment
The following estimates are from Prevent Blindness America (National Society to Prevent Blindness, 1980) and reflect 1978 estimates. While these estimates are not recent, they are the only comprehensive statistics which could be located which indicate the percentage of all cases of blindness accounted for by each disease (for all ages and ethnic groups).
Existing Cases of Legal Blindness
(Based on the number of legally blind persons in the population at a given time).
The leading causes of existing cases of legal blindness and the percentage of cases of legal blindness caused by each are as follows:Glaucoma (12.5)
Macular degeneration (11.7)
Cataract (8.3%)
Optic nerve atrophy (7.0)
Diabetic retinopathy (6.6)
Retinitis pigmentosa (RP) (4.7)
Myopia (4.0)
-
All other/unknown (45.2)
New Cases of Legal Blindness
(New cases of legal blindness which occur during the year)
The leading causes of new cases of legal blindness and the percentage of cases of legal blindness caused by each are as follows:Macular degeneration (16.8%)
Glaucoma (11.5%)
Diabetic retinopathy (10.1%)
Cataract (9.8%)
Optic nerve atrophy (4.3%)
All other/unknown (47.5%)
Macular Degeneration
According to The Eye Diseases Prevalence Research Group (2004a), age-related macular degeneration is the leading cause of blindness among European-descended people older than 65 years (p. 564).
Macular degeneration affects more than 1.75 million individuals in the U.S. This number is expected to increase to almost 3 million by 2020 due to the rapid aging of the U.S. population (The Eye Diseases Prevalence Research Group, 2004a).
An estimated 9 million persons in the U.S. have some form of age-related macular degeneration (1.75 million have AMD and 7 million are at substantial risk of developing AMD) (The Eye Diseases Prevalence Research Group, 2004 a).
An estimated 5% of people age 65 and older in the U.S. have some visual impairment as a result of macular degeneration (National Advisory Eye Council, 1993). Based on 2000 population estimates, this represents approximately 1.7 million older persons.
As the U.S. population ages, more elderly persons will become blind from macular degeneration than from glaucoma and diabetic retinopathy combined (National Advisory Eye Council, 1998, p.14).
Glaucoma
Approximately 2.2 million Americans (1.9%) age 40 and older, have glaucoma (Prevent Blindness America, 2002).
It is projected that the number of Americans with open-angle glaucoma will increase to more than 3 million by 2020 (The Eye Diseases Prevalence Research Group, 2004b).
About 163,000, or 2%, of persons age 40 and older in New York State have glaucoma (Prevent Blindness America, 2002).
Ethnic differences in the prevalence of glaucoma are evident as indicated in the following estimates:
Almost 4% of African-Americans (409,643) (age 40 and over) are reported to have glaucoma as compared to about 1.7% of Caucasians (1.6 million) and 1.5% of Hispanics (131,654) (Prevent Blindness America, 2002).
Based on findings from the Baltimore Eye Survey, the prevalence of vision impairment due to glaucoma is four to six times higher among African-Americans than Caucasians (Tielsch, Sommer, Witt, Katz, & Royall, 1990).
Research on a population-based sample found that glaucoma is the leading cause of blindness among Hispanics (Rodriguez, 2002).
Cataract
NOTE: - A review of the available data revealed that prevalence estimates of cataract vary considerably among different sources. According the National Advisory Eye Council, "Data on cataract blindness and cataract surgery provide incomplete information about the magnitude of the cataract problem. Large numbers of persons with visual impairments from cataract are not included in these data because their impairment is not sufficient to require surgical correction or to result in blindness" (1993, p. 156), or they may not be aware that they have the condition. Furthermore, as indicated by the Cataract Management Guideline Panel (1993), a problem in determining the prevalence of cataracts is the varying definitions used in the literature (e.g., presence of lens opacities; loss of visual acuity).
Estimates Based on Clinical Data:
Cataract affects 20.5 million (1 in 6) Americans age 40 and older. By 80 years of age, more than one half of Americans have cataract (Prevent Blindness America, 2002).
By 2020, the number of persons who have cataract is estimated to increase to 30.1 million by 2020 (The Eye Diseases Prevalence Research Group, 2004b).
There appears to be a higher prevalence of cataracts among females. According to estimates of Americans age 40 and older, a higher proportion of females have cataracts (20%) as compared to males (14%) (Prevent Blindness America, 2002).
In the Framingham Eye Study, cataract (defined as lens opacities accompanied by visual acuity of 20/30 or worse, including aphakics) was found in 5% of persons age 55-64, 18% of persons age 65-74, and 46% of persons age 75-84. Lens opacities (including aphakics) were found in 42% of persons age 55-64, 73% of persons age 65-74, and 91% of those 75-84 (Cataract Management Guideline, 1993).
- The 1971-1972 National Health and Nutrition Examination Survey of the National Center for Health Statistics reported that 28.5% of persons 65-74 had lens opacities accompanied by a decrease in visual acuity (20/25 or worse). Lens opacities were present in 58% of persons in this age group (National Advisory Eye Council, 1993; Cataract Management Guideline Panel, 1993).
Estimates Based on Self-Report
Based on data from the 1996 National Health Interview Survey, 15% of persons between 65-74 (2.8 million) and 20% of persons age 75 and older (2.7 million) self-report the presence of cataracts (Adams, Hendershot, & Marano, 1999).
Diabetic Retinopathy
An estimated 20.8 million people in the U.S. have diabetes. Of those, 6.2 million are undiagnosed(American Diabetes Association, n.d.,a).
Approximately 40% (6 million) of all people with diabetes have diabetic retinopathy. An estimated 5% of persons with diabetes have the sight-threatening form of this disease (Prevent Blindness America, 1994).
An estimated 5.3 million Americans age 18 and older have diabetic retinopathy (2.5%) (Prevent Blindness America, 2002 ).
Annually, 12,000 to 24,000 people lose their sight from diabetic retinopathy (American Diabetes Association, n.d.,b).
Diabetes is the leading cause of new cases of legal blindness among adults 20 to 74 years of age (American Diabetes Association, n.d.,b).
Among persons with juvenile diabetes, 25% will have diabetic retinopathy after 5 years; almost 60% after 10 years; and 80% after 15 years (Prevent Blindness America, 1994).
Mexican Americans are almost twice as likely and non-Hispanic blacks are almost 50% as likely to develop diabetic retinopathy as non-Hispanic whites, (American Diabetes Association, n.d.,b).
AIDs Related Visual Impairment
The estimated proportion of persons with AIDS who will develop CMV retinitis ranges from 20% (Jabs, Davis, & Mowyer, 1992) to approximately 40% (cited in Gallant, et al. (1992).
Cancer
Retinoblastoma is the most common intraocular malignancy of childhood. There are between 300 and 400 new cases diagnosed annually (National Advisory Eye Council, 1998).
Approximately 1,500 new cases of choroidal melanoma are diagnosed annually (National Advisory Eye Council, 1998).
Corneal Disease
Diseases and injury to the cornea are the leading cause of visits to physicians for medical eye care in the United States (National Advisory Eye Council, 1998).
Low Birth Weight
Blindness occurs mainly among children with birth weights below 1,000 grams (2 lbs, 3 oz) at rates of 5% to 6% (Hack, Klein, & Taylor, 1995).
Retinitis Pigmentosa
Retinitis pigmentosa is the most common cause of inherited blindness (National Advisory Eye Council, 1993).
Retinitis pigmentosa, for which there is no known cure, affects 100,000 Americans (Foundation Fighting Blindness).
An estimated one out of 80 people carry the recessive gene for RP (National Advisory Eye Council, 1993).
Usher Syndrome
The following estimates are from Foundation Fighting Blindness (2004):
There are about 10-15,000 people with Usher Syndrome.
Usher Syndrome is the major cause of deaf-blindness.
Refractive Errors
Myopia (nearsightedness) affects more than 30.5 million Americans age 40 and older (26%) (Prevent Blindness America, 2002).
Hyperopia (farsightedness) affects 12 million Americans age 40 and older (10%) (Prevent Blindness America, 2002).
It is estimated that between 1% and 4% of the childhood population are affected by strabismus and 1% to 2% suffer from amblyopia (National Advisory Eye Council, 1993).
In the United States, less than 2% of all children beginning school (age 5) are myopic. By the end of grade school (age 11 or 12) more than 15% are myopic. By adulthood, about 25% Americans are myopic, thereby requiring some form of optical correction to see clearly beyond an arm's length (National Advisory Eye Council, 1993, p. 247).
Although amblyopia, strabismus, nystagmus, and myopia seldom cause legal blindness they produce substantial visual loss that interferes with learning and working, and the overall quality of life (National Advisory Eye Council, 1993).