Reliability of the time trade-off technique of utility assessment in patients with retinal disease

Background: Studies in medical fields other than ophthalmology have given c onflicting results regarding the reliability of the time trade-off techniqu e of utility assessment. We performed a study to determine the test-retest reliability of the time trade-off technique for assessing utilities in pati ents with ocular diseases of the retina and to investigate possible factors associated with differences in utility over time. Methods: Patients referred to the retina service of a tertiary care hospita l in eastern Canada were eligible for the initial interview if they had bes t corrected vision of 20/30 or worse in at least one eye and were deemed co mpetent to answer the required questions. Patients were interviewed prospec tively between December 1999 and March 2000 during a normal 30-minute perio d needed for pharmacologic mydriasis to occur. Demographic, clinical (inclu ding Snellen visual acuity) and time trade-off utility information was coll ected through chart review and standardized interview. Patients who complet ed the interview successfully were called back 28 days later for follow-up. Results: Of the 138 eligible patients 112 (81.2%) completed the initial int erview. Of the 112, 96 (85.7%) completed the second interview. Half of the respondents were women, and all but one respondent were white. The mean age was 65.3 years. The primary reasons for visual loss included diabetic reti nopathy (59 patients [61.4%]) and age-related macular degeneration (14 pati ents [14.6%]). The intraclass correlation coefficient between the initial a nd follow-up visual utilities was 0.7634 (95% confidence interval 0.6655-0. 8355). Interpretation: Our results show excellent reliability of the time trade-of f technique of utility assessment in patients with ocular diseases of the r etina.