Preference-based quality of life measures in people with visual impairment.

The use of preference-based measures of quality of life represents the application of principles of decision theory and welfare economics to the measurement of health-related concepts. In this Perspective, we present the theoretical basis of preference-based measures in the assessment of the impact of vision-related disease on quality of life and their role in cost-effectiveness analysis. We discuss the use of the standard gamble and time trade-off in eliciting utilities and the limitations of both methods. Scaling issues related to utility are discussed, in particular the reasons for use of the "policy scale" (i.e., a scale where utilities are anchored at 1.0 for perfect health and 0 as death). This is contrasted with the use of the "vision-truncated scale" (i.e., a scale with 1.0 representing perfect vision and 0 being death), which is commonly used in assessment of vision-related utilities. We discuss problematic aspects of using the truncated scale in conducting cost-effectiveness research for vision-related disease, and provide a theoretical and empirical discussion of these limitations. In particular, we point out how these results raise questions concerning the conceptual relationship between vision- and health-related quality of life. Finally, we present the results of previous cross-cultural and trans-national studies of vision-related quality of life to demonstrate how utility studies might provide insight into the meaning of disease across cultures.