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A weighted version of the Melbourne Low-Vision ADL Index: a measure of disability impact
S A Haymes1, A W Johnston, A D Heyes
1Department of Optometry and Vision Sciences, University of Melbourne, Carlton, Victoria, Australia. s.haymes@optometry.unimelb.edu.au
Objective:
To develop a version of the Melbourne Low-Vision ADL Index that measures the personal impact of disability in activities of daily living (ADL's). Also, to determine the relationship between clinical measures of vision impairment and disability impact.
Methods:
The Melbourne Low-Vision ADL Index (MLVAI) is a desk-based clinical assessment of disability in ADL's. Ability to perform each item is rated on a five-level descriptive scale from zero to four. In this study, the original version of the MLVAI was modified to measure disability impact. The simple modification involved weighting each item by the importance of that item to the person being tested. Importance was also rated on a five-level scale from zero to four. The validity and reliability of the Weighted Melbourne Low-Vision ADL Index (MLVAI(W)) was determined for 97 vision-impaired subjects in a cross-sectional study.
Results:
Cronbach's alpha coefficient indicated an internal reliability of 0.94, and an intraclass correlation coefficient indicated an overall reliability of 0.88. The standard error of measurement was 24.7 points (out of a possible score of 400). There was a statistically significant difference in test scores between normal subjects and vision-impaired subjects. All vision measures had a high, statistically significant correlation with MLVAI(W) score. Near-word acuity had the strongest correlation (r(s) = 0.78, p < 0.001), followed by Melbourne Edge Test contrast sensitivity (r(s) = -0.72, p < 0.001). Visual field had the weakest correlation (r(s) = -0.52, p < 0.001). The best predictive model of MLVAI(W) score incorporated the variables age, near-word acuity, and visual field. Together, these variables accounted for 65.1% of the variance in MLVAI(W) score.
Conclusions:
The MLVAI is highly valid and reliable when weighted by a scale that reflects the personal importance of ADL's. The MLVAI(W) can provide information over and above that obtained with the usual clinical vision measures and may be used to assess low-vision patients and to measure low-vision rehabilitation outcomes. It is suggested that the assessment of disability using the original MLVAI and the assessment of the impact of disability using the MLVAI(W) should be kept separate to facilitate the clear interpretation of the outcomes of low-vision rehabilitation.