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Utility theory was developed in the 1940s to help quantify the uncertainty that existed in varied fields. 1 In the past 20 years, the application of utility theory to health care was undertaken to help quantify uncertainty regarding medical diagnostic and therapeutic procedures. 1-3 In essence, the utility value of a patient is a direct reflection of patient preferences. Utility assessment evaluates how effectively a patient is able to function in his or her activities of everyday life and allows an objective measurement of quality of life associated with a health (disease) state.
By convention, a utility (or utility value) of 1.0 indicates a state of perfect health, whereas a utility of 0 indicates death. Diseases that impair quality of life minimally, such as treated systemic arterial hypertension, may cause only a minimal decrease in utility to the 0.95-0.99 range, 2 whereas those that affect lifestyle dramatically, such as severe stroke, can markedly decrease the utility to 0.30. 4
Blindness has been reported by Torrance and Feeny 2 to be associated with a utility of 0.39, although the definition of blindness was not elaborated. Legal blindness of an eye is typically defined in many countries as Snellen visual acuity [= or <, slanted]20/200 in that eye. 5 Therefore, blindness could refer to vision ranging from 20/200 to no light perception. It was the authors' opinion that there might be a widely varying degree of patients' perception of their quality of life within the range of vision that qualifies as legal blindness. In particular, it was believed that those with no vision whatsoever had substantially more difficulty with the daily activities of life than those with limited vision. For this reason, a study was undertaken to determine utility values associated with theoretical total blindness (no light perception in each eye) and compare them with utility values encountered with other levels of legal blindness (vision [= or <, slanted]20/200) that were not as severe.
Methods
STUDY POPULATION AND SETTING
Consecutive ambulatory patients from the office practice of one physician at Wills Eye Hospital (GB) were selected for study. The patients were all adults taken predominantly from a vitreoretinal population. Included among the diseases that caused the visual loss were retinal detachment, age related macular degeneration, diabetic...