Prevalence of Visual Impairment in the United States: Ease versus Accuracy

      “When I use a word…it means just what I choose it to mean – neither more nor less.”– Humpty Dumpty, in Through the Looking Glass, Lewis Carroll (1871)
      “Variability of Vision Health Responses Across Multiple National Survey in the United States,”
      • Rein D.B.
      • Lamuda P.A.
      • Wittenborn J.S.
      • et al.
      Vision impairment and blindness prevalence in the United States: variability of vision health responses across multiple national surveys.
      (see page 15) documents wide variability in estimates of visual impairment and blindness prevalence in the United States when surveys use participant self-assessment. This is a problem that epidemiologists have long recognized.
      Objectively assessing an individual’s state of health and disability by direct examination is far more accurate than an individual’s self-assessment, even when the self-assessment is based on questions related to specific tasks. I first learned this lesson nearly half a century ago, when serving on a National Academy of Sciences committee tasked with constructing questions that might serve as valid indicators of visual ability. After several meetings, I convinced myself (and therefore, my nonophthalmic colleagues) that one’s ability to “recognize a friend across the street” should scale with measured visual acuity. It didn’t, at least not to a useful degree. Those who claimed they could not recognize a friend across the street often had normal presenting acuity, while many who claimed they could were clinically blind (unpublished data, National Academy of Sciences).
      Obtaining accurate, objectively measured estimates of the prevalence of visual impairment and blindness is difficult enough: Examiners must be adequately trained and frequently retested for consistency; the population studied and rate of participation must be well defined and accurately assessed to ensure they are representative of the group to whom the results will be applied; and visual functioning must be carefully assessed, with and without spectacles that subjects might bring with them (“presenting acuity” or “uncorrected acuity”) and after careful refraction (“best-corrected acuity”). These are all measurements of their existing or potential visual status, not how they perceive their status or actually “function.”
      As the study by Rein et al
      • Rein D.B.
      • Lamuda P.A.
      • Wittenborn J.S.
      • et al.
      Vision impairment and blindness prevalence in the United States: variability of vision health responses across multiple national surveys.
      makes clear, careful measurement of an individual’s visual acuity (as assessed in the National Health and Nutrition Examination Survey) must often differ considerably from the same individual’s self-assessment of his/her visual functioning. This seeming discrepancy will vary with a host of factors, including the subject’s social, economic, educational, and cultural background. “Blindness” may mean something very different to a person in a job or social position with few visual demands than it might to a person in a highly technical profession.
      Why is this particularly important? Because a 2016 National Academies of Sciences, Engineering, and Medicine report (for which I was a reviewer) recommended obtaining frequent, accurate estimates of visual impairment and blindness in the United States as a basis for stimulating interest and efforts directed to eye health.
      National Academies of Sciences, Engineering, and Medicine
      Making Eye Health a Population Health Imperative: Vision for Tomorrow.
      Without accurate estimates of visual impairment and the toll it takes on American health and productivity, vision health would never receive the attention it deserves. But one could readily argue, as the analyses by Rein et al
      • Rein D.B.
      • Lamuda P.A.
      • Wittenborn J.S.
      • et al.
      Vision impairment and blindness prevalence in the United States: variability of vision health responses across multiple national surveys.
      suggest, that frequent, relatively inexpensive surveys recording a sample’s perception of their visual functioning are no substitute for accurate, standardized examinations by highly trained observers. Yes, the former can be inexpensive “add-ons” to other questionnaire surveys, but less frequent, more reliable examination surveys might well prove far more enlightening.
      Historical experience bears this out: The first widely quoted estimates of the prevalence of visual acuity and ocular disease in the United States came from the National Eye Health Examination Survey,
      • Ganley J.P.
      • Roberts J.
      Eye conditions and related need for medical care among persons 1-74 years of age: United States, 1971-72.
      a “survey” that turned out to be overambitious, using a host of ophthalmology residents of varying training, supervision, and commitment. The results, although interesting as the first of their kind, were never considered particularly accurate. This helped give rise to more closely supervised, intensive examinations of limited, but well-defined populations, as in the Baltimore Eye Survey
      • Tielsch J.M.
      • Sommer A.
      • Witt K.
      • et al.
      Blindness and visual impairment in an American urban population.
      and subsequently similar undertakings in London, Rotterdam, and elsewhere.
      The most important contribution of Rein et al
      • Rein D.B.
      • Lamuda P.A.
      • Wittenborn J.S.
      • et al.
      Vision impairment and blindness prevalence in the United States: variability of vision health responses across multiple national surveys.
      might well be their illumination of the shortcomings of assessing the prevalence of visual dysfunction by merely questioning survey subjects.

      References

        • Rein D.B.
        • Lamuda P.A.
        • Wittenborn J.S.
        • et al.
        Vision impairment and blindness prevalence in the United States: variability of vision health responses across multiple national surveys.
        Ophthalmology. 2021; 128: 15-27
        • National Academies of Sciences, Engineering, and Medicine
        Making Eye Health a Population Health Imperative: Vision for Tomorrow.
        2-5. The National Academies Press, Washington, DC2016: 2-12
        • Ganley J.P.
        • Roberts J.
        Eye conditions and related need for medical care among persons 1-74 years of age: United States, 1971-72.
        Vital and Health Statistics. Series 11, 1983
        • Tielsch J.M.
        • Sommer A.
        • Witt K.
        • et al.
        Blindness and visual impairment in an American urban population.
        The Baltimore Eye Survey. Arch Ophthalmol. 1990; 108: 286-290

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