Author: David P Crabb (United Kingdom)
Co-authors: Daniel S Asfaw, Nicholas D Smith, Deanna D Taylor
Purpose
Geographic atrophy (GA) can manifest as development of an absolute scotoma, an area of absence of function in the central retina. In turn, this can have a serious impact on health-related quality of life. New treatments for GA, which promise to halt or slow the progress of the disease, must be subject to health economic evaluation - these are not trivial exercises to do. Typically, regulatory bodies recommend that the public (not patients) value health states to derive utility values for economic evaluation of new treatments. We demonstrate how a computer-based gaze contingent simulated scotoma can be combined with a time trade-off (TTO) experiment to elicit utility values about severity of progressing scotoma in GA.
Setting/Venue
University based cross sectional study in people with normal vision.
Methods
Adults with normal vision were recruited and instructed to watch four films of everyday scenes shot from a point-of-view camera. Films were incorporated into a computer-based set-up, using an eye tracker, which applies a ‘simulated’ scotoma in correspondence to the user’s gaze. Before each film participants were told to imagine this condition would be their permanent vision. In experiment 1 participants viewed a film with a very large scotoma obscuring most (60%) of the screen followed by a film with a very small scotoma (2% of the screen) in the peripheral visual field. In experiment 2 participants viewed two ‘realistic’ central scotoma calculated from microperimetry measurements taken in GA patients; these conditions were similar but obscured 5% and 8% of the film respectively, with the latter encroaching on the point of regard, mimicking how GA might progress to foveal involvement. After each film, participants were asked to choose between 10 years of life with the condition they just observed versus varying amounts of perfect vision in 1-year decrements from 10 to 0 years. The difference between their choice is the number of years of perfect health they would trade to avoid the condition with the scotoma (TTO value [years]).
Results
Seventy-five young adults (52 female; median [interquartile range] age of 21 [20 to 22] years) with normal or correct-to-normal vision, established by a short optometric examination, completed the study. Each participant session lasted approximately 30-40 minutes. Films/conditions were presented in random order. In experiment 1, mean (SD) TTO value for the very large and very small scotoma was 5.0 (2.7) and 1.9 (1.4) years respectively. This means, for example, for a 10-year period, participants were prepared on average to trade 5.0 (95% confidence interval [CI]: 4.4-5.6) years of perfect health to avoid ten years of life with the very large scotoma. The mean (95%CI) difference of 3.1 (2.6, 3.6) years between the conditions in experiment 1 demonstrates the utility and good understanding of the task. In experiment 2 the mean (SD) TTO value for two realistic scotoma was 2.6 (1.9) and 3.5 (2.1) years respectively; the mean (95%CI) difference of 0.9 (0.5, 1.3) years was clearly different from zero and was statistically significant (P=0.001). This is an important result suggesting that even relatively small differences in 'GA like scotoma' can be quantified as preferred years of perfect vision in a TTO experiment in volunteers with normal vision.
Conlusions
We have shown how a computer based gaze contingent simulated scotoma can be combined with a TTO experiment to elicit utility values about severity of progressing scotoma in GA from people with normal vision. Specifically we have evidence that relatively small differences in GA like scotoma can be quantified as preferred years of perfect vision. In economic evaluation of healthcare interventions, utilities represent the strength of individuals’ preferences for different health states. Conventionally the valuations fall between 0 and 1, with 1 representing the valuation of a state of perfect health. TTO experiments are accepted to be a direct method for calculating a utility and our value for the difference between the progressing GA like scotoma would be considered 0.09; this is a significantly large utility value. Our methodology for eliciting utility values for vision impairment in members of the public may be preferable to previous approaches (e.g. obscuring contact lens) and will be useful in health economic evaluation of promised treatments for slowing progression of GA or other eye diseases that manifest scotoma.
Financial Disclosure
DPC: Allergan, Bayer, Santen, THEA (Honoraria); Allergan, Apellis, Roche, Santen (Unrestricted funding); Centervue, Apellis (Consultant)
Comments
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