Evaluation of a Vision-Related Utility Instrument: The German Vision and Quality of Life Index
ABSTRACT PURPOSE: Multi-attribute utility instruments (MAUIs) which contain a descriptive system including several health dimensions with associated levels of increasing severity are commonly used to measure utilities. However, the validity of the descriptive systems is rarely examined using modern psychometric theory. Therefore, we evaluated the psychometric properties of the German version of the Vision and Quality of Life Index (VisQol), a six item vision-related MAUI. Methods: The German VisQol was self-administered to 340 patients and 280 controls. All subjects underwent a full ophthalmological examination including best-corrected visual acuity (VA) testing. The psychometric properties of the VisQoL were assessed using Rasch analysis. Results: The VisQoL's descriptive system did not function in controls. In patients, after collapsing response categories to resolve disordered thresholds, and omitting misfitting persons, the measurement properties (i.e. precision, unidimensionality and targeting) of the German VisQoL were satisfactory. Most person misfit related to unexpected responses to item four ('organizing assistance'). Rasch generated person estimates were not different between age categories, gender or underlying ocular condition, but decreased significantly with presence of visual impairment in the better eye (LogMAR≥0.5, 1.20±4.62 compared to 3.46±3.52, p<0.001). Conclusions: The German VisQoL's descriptive system displayed adequate fit to the Rasch model after removal of a large proportion of patients with poor fit statistics. However, the wording of item four should be revised in order to reduce respondent confusion and measurement 'noise'. The scale's descriptive system does not function in a sample of visually unimpaired persons most likely due to a lack of variance in the measured trait.
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ABSTRACT: A multi-attribute utility instrument (MAUI) consists of a descriptive system in which the items and responses seek information about a concept of the universe of health-related QoL, and responses to these items are then weighted and combined to produce the index. The 6-item Vision and Quality of Life Index (VisQoL) is the only available vision-related MAUI, developed and validated in Australia, specifically for visually impaired (VI) populations.. The psychometric properties of the VisQoL have not yet been investigated in an Indian VI sample; this was the aim of the present study. The Indian VisQoL was administered to 349 VI adults face-to-face by a trained interviewer at the Vision Rehabilitation Centres of a tertiary eye care facility, South India. Rasch analysis was used to assess the psychometric properties. Rescoring was necessary for all except one item before ordered thresholds were obtained. All items fit the Rasch model and unidimensionality was confirmed. Person separation was acceptable (2.01) indicating that the instrument can discriminate among three strata of participants' vision-related QoL (VRQoL). The VisQoL items were substantially targeted to the participants' VRQoL (- 0.69 logits). One item ('ability to have friendships') demonstrated large differential item functioning by work status; working participants reported the item to be more difficult (-1.13 logits) relative to other items when compared to the non-working participants. The 6-item Indian VisQoL satisfies unidimensional Rasch model expectations in VI patients. Disordering of response categories was evident; replication is required before a common rescoring option should be considered.Investigative ophthalmology & visual science 06/2013; 54(7). DOI:10.1167/iovs.13-11892 · 3.66 Impact Factor
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ABSTRACT: Purpose Patients with eye diseases often have a better-seeing eye (BSE) and a worse-seeing eye (WSE). This review will carve out the current knowledge in which the relationship to BSEs and WSEs contributes to overall visual functioning and vision-related quality of life (VRQoL). Methods Searches were from database inception to the current date. Terms used for the search were “better eye”, “worse eye”, “utility”, “life quality”, “quality of life”, “VFQ-25”, and “visual acuity”. Results There is a lack of a clear definition for BSE and WSE, and the used definitions are regularly dependent on the underlying eye disease. “BSE” and “WSE” can interact in terms of binocular inhibition or summation. Measured influences of the BSE and WSE on VRQoL are dependent on the underlying instrument used for the measurement. Several studies show impaired VRQoL if only one eye is affected from disease, with unimpaired vision of the BSE. VRQoL can improve significantly when treating the BSE and the WSE. In eye diseases with impairment of the central vision, there is a better correlation between the BSE and VRQoL. However, in eye diseases with peripheral vision impairment, eg, glaucoma, functional parameters of the WSE are better predictors for VRQoL. Conclusion The WSE appears to have a stronger influence on VRQoL than is generally assumed. This is especially the case if the underlying eye disease does not affect central vision but peripheral vision.Clinical ophthalmology (Auckland, N.Z.) 09/2014; 8:1703-9. DOI:10.2147/OPTH.S64200