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Huibert Simonsz, Elizabeth van de Graaf, Joost Felius, Gerard Borsboom, Hendrikus Kelderman; Principal component analysis of both AS-20 and A&SQ questionnaires in 110 subjects of the historic Waterland cohort. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3645.
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© ARVO (1962-2015); The Authors (2016-present)
The AS-20 questionnaire was presented to the historic Waterland cohort, who had been treated for amblyopia and strabismus by the only orthoptist in Waterland in 1968-73, filled out the A&SQ in 2003, and were re-examined in 2004 (N=137), to determine with factor analysis whether the domains of AS-20 and A&SQ correlated with similar aspects of underlying quality of life.
After fruitful preliminary analysis in 86 patients, remaining persons re-examined in 2004 were approached. With common-factor analysis the overlap was assessed between the AS-20 subscales: psychosocial (10 questions) and functional (10) and the prehypothesized domains of the A&SQ: fear to loose function of the better eye (2), depth vision (10), visual disorientation (3), double vision (3) and psychosocial (5). We applied common-factor analysis of the polychoric correlation-matrix. Values were imputed for missing answers and non-applicable questions. The analysis resulted in factor loadings, i.e. correlations of the questions with the factor. Their relation with past and present orthoptic findings was explored.
The analysis was extended to 110 persons. Common factor analysis showed 3 factors explaining 48.7% of the variance in answers. The psychosocial domains of both questionnaires overlapped (figure shows Factor 1 and 3 loadings). With 10 questions in A&SQ’s depth domain, only AS-20 #14 overlapped: “I have problems with depth perception”. Eight questions of the AS-20’s functional domain “I avoid reading because of my eyes”,“I stop doing things because my eyes make it difficult to concentrate”,“My eyes feel strained”,“I have problems reading because of my eye condition”,“I feel stressed because of my eyes”,“I worry about my eyes”,“I can’t enjoy my hobbies because of my eyes”,“I need to take frequent breaks when reading because of my eyes” constituted a separate group with no overlap with the A&SQ.
Discrepancies result from the different ways the 2 questionnnaires were made: The influence of lack of depth vision on quality of life of strabismus patients was overestimated when the prehypothesized domains of the A&SQ were conceived. Asthenopia is frequent among outpatient-clinic strabismus patients, the original source of the AS-20 questions and, hence, predominates its functional domain, but asthenopia was considered too aspecific for amblyopia and strabismus when the A&SQ was made.
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