Visual impairment is increasing among American adults

Image: PD/Laser therapy in Diabetic Retinopathy

Key study points:

1. Nonrefractive visual impairment (NVI) has increased by 21% from 1999-2002 and 2005-2008.
2. The prevalence of a diabetes diagnosis of 10 years duration or longer, a risk factor for NVI, rose from 2.8% to 3.6% between 1999-2002 and 2005-2008.

Primer: Visual impairment can be divided into the refractive and nonrefractive categories; the latter group refers to defects that cannot be corrected using eyeglasses or contact lenses. Common causes of NVI include glaucoma, macular degeneration, and diabetic retinopathy. Diabetic retinopathy is the leading cause of blindness among US adults aged 40 and older. Diabetes mellitus prevalence has been increasing amongst 20-40 year olds, rising from 2.1% in 1990 to 3.7% in 1998. Given the intimate connection between diabetic retinopathy and NVI, the present study attempted to assess whether changes in the rate of NVI diagnosis reflect the growing prevalence of diabetes, and thus diabetic retinopathy, in the past several years.

Background reading:

1. Causes and prevalence of visual impairment among adults in the United States [Arch Opthalmol]
2. Diabetes mellitus and visual impairment: national health and nutrition examination survey, 1999-2004 [Arch Ophthalmol]

This [retrospective cross-sectional] study: The authors of this study utilized data from the NHANES database collected during two time periods, 1999-2002 & 2005-2008. Visual acuity and demographics for all patients above 20 years old were noted. Nonrefractive visual impairment (NVI) was designated as visual acuity of 20/40 or less that remained uncorrected after refraction. Further, risk factors including BMI, hypertension, hyperlipidemia, diabetes of 10 years duration or more, and education level were also assessed.

Prevalence of NVI rose from 1.4% in the 1999-2002 period to 1.7% in 2005-2008, reflecting a significant 21% increase. This rate of change was highest among young non-Hispanic Caucasians. Diagnosis of diabetes was the only risk factor that demonstrated a significant change in prevalence during the 2005-2008. Odds ratios of the association between NVI and diabetes diagnosis were 1.93 in the 1992-2002 period and 2.67 in the 2005-2008 period.

In sum: This publication is the first study to demonstrate a significant chronologic increase in NVI. Further, the results indicate an increase in the overall prevalence of long-standing diabetes amongst younger adults (20-40 years old), which may explain association between diabetes diagnosis of at least 10 years and NVI. Indeed, this connection poses significant public health implications, as it suggests that longstanding diabetes may put patients at risk for ophthalmic complications and that the rise in NVI in the past decade may at least be partially explained by the growing diabetes epidemic. The results of this study highlight the importance of diabetes prevention among young adults and the crucial need for improvements in eye care among diabetics, especially given the costly nature of NVI management.

Strengths of this study include the use of NHANES, a rigorous database containing a large and representative sample and data that reflects both subjective (interviews) and objective (exams) measures. Weaknesses of the paper include the use of an autorefractor to assess visual acuity, as this has not been shown to be equivalent to a physician’s exam. In addition, the cause of NVI was not identified in the NHANES database. While the authors concluded that macular degeneration, cataract, or glaucoma in the 20-40 year old population is extremely rare and thus likely related to the diagnosis of diabetes in this age group, there remains the possibility of underlying confounders that may not have been controlled for. Thus, the study would have been stronger if the specific cause of NVI had been identified.

Click to read the study in JAMA

Click to read the accompanying editorial in JAMA

By [SSS] and [MK]

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