The Impact of Anchor Point on Utilities for 5 Common Ophthalmic Diseases
Received 31 October 2006; received in revised form 5 June 2007; accepted 5 June 2007. published online 10 September 2007.
Purpose
To elicit utilities on a perfect health and perfect vision scale for 5 common eye diseases.
Design
Cross-sectional observational preference study.
Participants
We included 434 patients: 58 with diabetic retinopathy, 99 with glaucoma, 44 with age-related macular degeneration (AMD), 124 with cataract; 109 with refractive error.
Testing
Standard gamble utilities were estimated using a computer-based preference assessment interview platform.
Main Outcome Measures
Standard gamble utilities, a quality-of-life measure that examines the willingness to accept a risk of death or unilateral blindness in return for perfect health or perfect vision.
Results
Using the standard policy scale, where health equivalent to death is 0 and perfect health is 1, participants with asymptomatic diabetic retinopathy had a utility of 0.93. By comparison, symptomatic diabetics had a further utility loss of 0.14. Asymptomatic glaucoma participants had a utility of 0.92 with a decrease of 0.03 for early field loss and a further decrease of 0.03 with central field loss. Participants with AMD who had ≥20/100 better-eye visual acuity reported a utility of 0.89, whereas those with more severe AMD reported 0.76. However, neither clinical cataract opacity score nor refractive error correlated with utility. Adjustment for age and comorbidity did not alter these relationships. For the same participants, utilities measured with different anchor points—monocular blindness as 0 and perfect vision as 1—were lower, especially among participants with increased disease severity. The difference between utility assessed on this perfect vision–blindness scale and the perfect health–death scale ranged from 0.04 for those with severe refractive error to 0.19 for symptomatic diabetics and 0.37 for those with severe AMD.
Conclusions
This paper elicits utilities with different anchor points from a previously unreported sample of 434 patients. Lower utility scores normally imply greater benefit with successful treatment or prevention of disease, but switching from the conventional policy scale to the perfect vision scale also consistently results in lower scores. Because most previous ophthalmic studies have used perfect vision as the upper anchor, the resulting utilities may not have been accurate.
Available online: September 12, 2007.
1Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri.
2Department of Biostatistics, Washington University School of Medicine, St. Louis, Missouri.
ABSTRACT