Wednesday, January 03, 2007

What is the link between being visually impaired and Diabetes?

Persons with diabetes are more likely to be visually impaired than persons without the disease.

1 In 2005, CDC estimated that 14.6 million persons in the United States had diagnosed diabetes and an additional 6.2 million had undiagnosed diabetes.

2 Despite the importance of detecting and treating vision problems caused by refractive errors (i.e., correctable visual impairment [CVI]), a limited number of studies have attempted to determine the proportion of persons with diabetes whose poor vision could be corrected with accurately prescribed glasses or contact lenses.

To estimate that proportion, CDC analyzed 1999-2004 data from the National Health and Nutrition Examination Survey (NHANES). This report describes the results of that analysis, which indicated that among U.S. adults aged 20 years with diabetes,* 11.0% had visual impairment (i.e., presenting visual acuity worse than 20/40 in their better-seeing eye while wearing glasses or contact lenses, if applicable) and approximately 65.5% of these cases of visual impairment were correctable.

Health-care providers and persons with diabetes should be more aware that poor vision often is correctable and that visual corrections can reduce the risk for injury and improve the quality of life for persons with diabetes.

NHANES is an ongoing series of cross-sectional surveys on health and nutrition designed to be nationally representative of the noninstitutionalized, U.S. civilian population by using a complex, multistage probability design. All NHANES surveys include a household interview followed by a detailed physical examination. For the 1999-2000, 2001-2002, and 2003-2004 surveys, participants also were asked questions regarding vision function, and the physical examination included a vision examination in which visual acuity was measured before and after an objective autorefraction test (optical correction measured by an autorefractor).

In this study, visual acuity before correction was defined as distance visual acuity with whatever form of current correction (e.g., glasses or contact lenses) the participant might have worn at the time of examination. Visual acuity after correction was defined as potential visual acuity as assessed by an objective autorefraction test. Only those participants whose visual acuity before correction was worse than 20/30 were administered the autorefraction test. Diabetes was defined as a self-reported previous diagnosis of the disease.

In the NHANES surveys conducted during 1999-2004, the combined household interview response rate was approximately 82%, and the medical examination response rate was 77%. Of 15,332 adults aged 20 years, 22 were excluded because of lack of diabetes information or because their diabetes was diagnosed only during pregnancy. Another 2,306 adults for whom visual acuity before correction values were missing were excluded from the study.

For this analysis, 1,237 adults aged 20 years with self-reported diabetes were divided into three groups according to their visual acuity in the better-seeing eye (before and after optical correction): (1) normal: visual acuity of 20/40 or better; (2) mild impairment: visual acuity better than 20/200 and worse than 20/40; and (3) severe impairment: visual acuity of 20/200 or worse. The prevalence of CVI was defined as the proportion of adults with mild or severe impairment before correction who were found to have the potential for normal visual acuity after correction.

All analyses were weighted to make estimates representative of the U.S. civilian, noninstitutionalized population. Results also were analyzed by age group (20-64 years compared with 65 years), sex, and race/ethnicity (non-Hispanic white, non-Hispanic black, Mexican American, and other).

Overall, the prevalence of CVI among U.S. adults aged >20 years with diabetes was 7.2%, which indicated that the proper prescription for glasses or contact lenses would have restored normal visual acuity to 65.5% of visually impaired adults with diabetes.

The results indicated that 9.7% (95% CI [confidence interval] = 7.9%-11.8%) of U.S. adults with diabetes had mild visual impairment, and 1.4% (CI = 1.0%-1.9%) had severe visual impairment before correction; 2.9% (CI = 2.1%-3.9%) had mild impairment, and 1.0% (CI = 0.6%-1.5%) had severe impairment after correction. Approximately 0.3% of adults with diabetes who had severe visual impairment before correction had only mild visual impairment after correction. Thus, optical correction would have restored normal visual acuity to approximately 73.4% of adults with mild impairment and 9.1% of adults with severe impairment.

Although the crude prevalence of CVI among adults aged 65 years with diabetes (7.3%) was similar to that among those aged 20-64 years (7.2%), 89.2% of visual impairment cases among the younger age group were correctable, compared with 46.4% of cases among the older age group. The age-adjusted prevalence of CVI was similar among men (7.3%) and women (7.2%). Although not statistically significant, the age-adjusted prevalence of CVI was higher among non-Hispanic blacks (7.9%) and Mexican Americans (8.1%) than among non-Hispanic whites (5.6%).


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