Self-reported Assessment of Visual Function in a ...

Self-reported Assessment of Visual Function in a Population-Based Study: The SEE Project Marian Valbuena,1 Karen Bandeen-Roche,1 Gary S. Rubin,2 Beatrix Munoz? Sheila K. West,5 and the SEE Project Team PURPOSE. TO report

on the usefulness of the Activities of Daily Vision Scale (ADVS) questionnaire for assessing visual functioning, a population-based sample of elderly Americans.

The ADVS questionnaire was administered to a population-based sample of 2520 community-dwelling individuals 65 to 84 years of age in Salisbury, MD. Items and subscales were evaluated for internal consistency, item discrimination, and content validity. Published subscale groupings and item associations in our population were compared for coherence using correlation, factor, and cluster analyses. Whole-sample and race- and gender-specific analyses were conducted. External validity was explored by regressing ADVS scores on standard psychophysical vision measures. METHODS.

RESULTS. ADVS scores were skewed to high visual functioning levels; approximately 60% of the population had function scores of 95 or better (of a possible 100). The overall, night driving, and near vision scales were internally consistent and had strong item-subscale associations; the day driving and glare subscales were not acceptable regarding these properties. The far vision subscale was acceptably scalable but only weakly differentiated from the other subscales. Overall, night driving, near vision, and far vision scores were all statistically and independently associated with multiple psychophysical vision measures. Findings were consistent across race and gender subgroups. CONCLUSIONS. AS assessed by the ADVS, reported visual functioning is high in our representative older population. The overall scale and selected subscales effectively distinguish persons along a spectrum of ability. They correlate with measures of visual impairment in a reasonable way and thus hold promise for risk factor investigations. The published day driving and glare subscales should be examined for relevance and consistency before being applied in population-based settings. Methods specific to population-based settings should be investigated for their ability to better elicit additional visual function dimensions and early visual disability. {Invest Ophthalmol Vis Set. 1999; 40:280-288)

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substantial volume of recent ophthalmologic research has been devoted to visual functioning measurement. This research focus has ample precedent in the general medical literature, in which numerous scales have been developed for self-report of physical functioning.7"9 Despite the recent advent of "performance-based" assessment of physical functioning,10" self-report measures persist as standard outcomes. One compelling reason for this is that the ultimate goal of therapy is to restore one's ability to function in

From the 'Department of Biostatistics, 2Lions Low Vision Center, and the 3Dana Center for Preventive Ophthalmology, Wilmer Institute, The Johns Hopkins University, School of Hygiene and Public Health, School of Medicine, Baltimore, Maryland. Supported by National Institute on Aging, Bethesda, Maryland, Grant PO1AG10184. SKW is a Research to Prevent Blindness Senior Scientific Investigator (Research to Prevent Blindness, New York, New York). KBR is a Brookdale National Fellow, Brookdale Foundation, New York, New York. Submitted for publication November 21, 1997; revised August 7, 1998; accepted August 19, 1998. Proprietary interest category: N. Reprint requests: Karen Bandeen-Roche, School of Hygiene and Public Health, Johns Hopkins University, Department of Biostatistics, 615 N. Wolfe Street, Room E3OO6, Baltimore, MD 21205-2179.

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everyday life. As useful as performance- and test-based measures are for tracking disease, then, it can be argued that they indirectly measure the day-to-day functioning outcome that is most relevant for evaluating treatments. A second reason is that self-reported functioning measurements are not merely surrogates of "more objective" performance measures but rather differ in content.12 Specifically, one's functioning in an everyday environment may differ dramatically from that in an exceptional, standardized setting. Moreover, it may vary systematically with nonphysiological factors among persons with similar physiological impairment. These considerations carry over to vision-related outcomes and are particularly important in epidemiologic investigations that aim to describe how physiological impairment affects one's usual functioning ability. In this article, we report on the self-reported visual functioning assessment of just such an investigation-the Salisbury Eye Evaluation (SEE) project. In the SEE project, the Activities of Daily Vision Scale (ADVS2) served as the primary assessment of self-reported visual functioning. Like many functioning questionnaires, it comprises items that elicit subjects' ratings of their level of difficulty doing various activities. The ADVS was chosen as the only standardized visual functioning instalment available at the time. 21314 Whereas the ADVS was designed as a tool to assess Investigative Ophthalmology & Visual Science, February 1999, Vol. 40, No. 2 Copyright © Association for Research in Vision and Ophthalmology

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treatment effectiveness in patients with cataracts, the SEE sample was selected to be representative of a community-dwelling older population without an a priori screening for visual status. This contrast is important because the goals of assessment differ substantially in patient- versus population-based settings. In evaluating treatment efficacy, it is necessary and appropriate to assess a wide range of activities hypothesized to be made difficult by the condition being treated. Often, there is no expectation that most individuals will engage in every listed activity. In a population-based study whose aim is to identify epidemiologic risk factors for functional decline, participants' functional status must be defined with as broad a severity range and as little incidental variation as possible. Of concern in using the ADVS for this purpose: there is no guarantee that activities that define a broad range of functioning in cataract patients will adequately distinguish severity in persons with much milder impairment, and the benefits of eliciting information about uncommon activities must be weighed against the incidental variability introduced by measuring function with very different activity profiles. Although ADV scales and subscales were reported to appropriately measure functioning in the cataract patient population on which it was developed, it is unknown whether these are effective for summarizing functioning data from representative older populations. This article reports self-reported visual functioning in the SEE population, as measured by the ADVS. Moreover, it examines the psychometric performance of the ADVS functioning measures in our population-based sample.

TABLE 1. Demographic Characteristics of Study

METHODS

Self-reported Visual Functioning Assessment

Study Population

The ADVS was administered as part of the in-home interview by trained interviewers. The instrument was read aloud to each participant as published excluding the question on the use of bus service, which is not available in Salisbury. This left questions on 21 daily activities related to visual functioning (Table 2). For each activity, participants were first asked whether they had done the activity within the previous 3 months. If so, the level of difficulty in doing the activity was scored (2 = extreme difficulty; 3 = moderate difficulty; 4 = a little difficulty; and 5 = no difficulty). Participants who had not done the activity in the previous 3 months were asked whether this was because of vision problems. If so, a most severe level of difficulty (1 = unable to do due to vision) was recorded; if not, the participant was not scored on the activity. The first data column (n) in Table 2 identifies how many persons had difficulty scores recorded for each activity. Nearly all persons not having difficulty scores reported not doing the activity for nonvision reasons, as opposed to having no response recorded at all. ADVS overall and subscale scores were calculated as follows. Each activity done recently or not done because of vision problems was given a score of 1 to 5, as described above. For each subscale, all recorded activity scores were averaged, eliminating activities not participated in for reasons other than vision. Then, the average subscale scores were rescaled to a range of 0 to 100, with 0 denoting responses of "unable to do due to vision" on all scored activities and 100 denoting responses of "no difficulty" on all scored activities. The overall score was computed by averaging all recorded activity scores and then rescaling to a range of 0 to 100.

The SEE study sample consisted of 2520 elderly communitydwelling individuals in the area of Salisbury, MD. This sample has been described in detail elsewhere.15 In brief, an age- and race-stratified random sample of 65- to 84-year-old residents in selected Maryland zip code areas was drawn from national Healthcare Financing Administration Medicare eligibility lists. All African Americans and approximately 60% of the white population were selected. Sampled persons were contacted in their homes by a trained interviewer, who assessed two additional eligibility criteria for inclusion in the SEE study: ability to leave home for a clinic visit (e.g., not bedridden) and a MiniMental State Examination (MMSE16) score of 18 or higher. Study participants were administered a 2-hour in-home interview followed within a few weeks by a 4- to 5-hour clinic examination. Informed consent was obtained from all study participants. The tenets of the Declaration of Helsinki were followed, and all procedures were approved by the Joint Committee on Clinical Investigation of The Johns Hopkins University School of Medicine. Among 3906 potentially eligible study candidates, 85 could not be contacted, 935 refused to participate at all, and 366 refused to participate in the clinic examination after completing the in-home interview. Overall, this gives an eligible participation rate of 65%. A detailed comparison of study participants and eligible persons who refused to participate is given in Munoz et al.17 In brief, study participants were younger, better educated, less likely to report poor health status, recent falls, or disability, and less likely to grade their vision as good, than were persons who refused to participate.

Participants Age at time of clinic exam

65-69 years 70-74 years 75-79 years 80-86 years Gender Male Female Race White African American Education 12 years Mini-Mental State Exam score