Vision and quality of life: the development of a utility measure

To identify the content for a vision and quality of life-related utility measure (Vision Quality of Life Index [VisQoL]) for the economic evaluation of eye care and rehabilitation programs.

Focus groups of the visually impaired elicited key concepts. Based on these and previous research, 33 items were generated. These were administered to visually impaired adults (n = 70) and a representative sample of unimpaired adults (n = 86). The item bank was reduced through examination of item properties, exploratory factor (EFA), item response theory (IRT), and structural equation modeling (SEM) analyses. The resultant model was confirmed through administration to a second sample of participants.

Focus group themes included physical well-being, social well-being, independence, self-actualization, emotional well-being, and planning and organization. Poorly performing items were eliminated on basic psychometric properties, including failure to discriminate. Next, EFA loadings were used to select items. Twelve items survived. To minimize redundancy, IRT analysis and SEM reduced the VisQoL item pool to six items (Cronbach alpha = 0.88). To confirm this model, these items were then administered to an additional 218 participants; 35% with a vision impairment. A pooled SEM analysis showed the model to have very good fit properties (root mean square error of approximation [RMSEA] = 0.000). A preliminary test of the model against visual acuity showed a significant monotonic relationship.

The short 6-item VisQoL has excellent psychometric properties as a simple summative instrument. It can be used in its present state as a condition-specific outcome measure for the evaluation of healthcare interventions for the visually impaired. The descriptive model is also suitable for generating utility values for the economic evaluation of vision-related programs and services.