The finding came from new research, conducted by a team at the Johns Hopkins University School of Medicine, Baltimore, and was published in JAMA, December 12 issue.
Background information in the report stated: "It is estimated that more than 14 million individuals in the United States aged 12 years and older are visually impaired (<20/40). Of these cases, 11 million are attributable to refractive error."
The most frequent reasons Americans experience nonrefractive visual impairment are:diabetes. Since the eye is one of the main organs impacted by diabetes, patients can develop certain visual conditions.
"The prevalence of diagnosed diabetes has increased among adults in recent years, rising from 4.9 percent in 1990 to 6.5 percent in 1998, 7.9 percent in 2001, 10.7 percent in 2007, and 11.3 percent in 2010," the authors explained.
The researchers, led by Fang Ko, M.D., set out to evaluate the prevalence of nonrefractive visual impairment and the risk factors associated with the condition.
Data was gathered and analyzed from the National Health and Nutrition Examination Survey (NHANES), a representative sample of the American population.
Questionnaires, physical exams, and laboratory tests were given to 9,471 and 10,480 subjects aged 20 and older in 1999-2002 and 2005-2008 respectively.
Participants were considered to have nonrefractive visual impairment when their visual acuity was less than 20/40 when measured by an autorefractor - a tool which evaluates a person's refractive error.
Results showed that the prevalence of nonrefractive visual impairment increased 21%, from 1.4% in 1999-2002 to 1.7% in 2005-2008. They also found that non-Hispanic whites experienced a 40% increase, from 0.5% to 0.7%.
The factors that were linked to nonrefractive visual impairment included:
- older age
- lower education level
- diabetes diagnosed at least 10 years ago
The researchers concluded:
"We report a previously unrecognized increase of visual impairment among U.S. adults that cannot be attributed to refractive error. If the current finding becomes a persisting trend, it could result in increasing rates of disability in the U.S. population, including greater numbers of patients with end-organ diabetic damage who would require ophthalmic care. These results have important implications for resource allocation in the debate of distribution of limited medical services and funding. Continued monitoring of visual disability and diabetes, as well as additional research addressing causes, prevention, and treatment, is warranted."