Patient-based health status measures have an important role to play in the assessment of health care outcomes. Among these measures, global assessments increasingly have been used, although the understanding of the performance of these indicators and the determinants of patients responses is underdeveloped. In this study, the performance of a single-item global indicator of visual function in cataract patients of four international settings was compared.
Visual acuity and ocular comorbidity was assessed by patients' ophthalmologist using Snellen-type charts in patients referred for a first cataract surgery in the United States, Manitoba (Canada), Denmark, and Barcelona (Spain). Patients also were interviewed by telephone and asked to report overall trouble with vision on a single-item indicator ("great deal," "moderate," "a little," "none") and to complete the Visual Functioning Index (VF-14), a scale of visual function ranging from 0 (worst function) to 100 (best level of function), along with other questions including the degree the patient was bothered by symptoms as measured by the Cataract Symptom Score (CSS). A total of 1,407 patients completed the clinical examination and the preoperative interview.
Distribution of overall trouble with vision varied across the sites, with the proportion of patients reporting a great deal of trouble ranging from 21.7% to 37.9%. In all sites, patients reporting more trouble with vision tended to show a poorer age-adjusted and sex-adjusted visual acuity. The proportion of patients reporting great deal of trouble with vision was higher in the groups with worse visual acuity (P < 0.001). In multivariate analysis, after controlling for clinical and sociodemographic factors, the patients from Manitoba (OR = 0.32, 95% CI = 0.20, 0.51) and those from Barcelona (OR = 0.33, 95% CI = 0.20, 0.56) were less likely to report a great deal of trouble with their vision (P < 0.01) than the Danish and US patients. No such differences were found among the US patients from three sites.
There is international variation in the self-reporting of global visionrelated functional capacity that is not explained by clinical or sociodemographic factors, which may be because of cultural differences. International comparisons of patient-based health outcomes should not rely only on single-item indicators until there is convincing evidence of their cross-cultural equivalence.
*From the Health Services Research Unit, Institut Municipal d'Investigació Mèdica (IMIM), Barcelona, Spain.
†From Community Health Sciences, Faculty of Medicine, University of Manitoba, Canada.
‡From the Institute of Social Medicine, Faculty of Medicine, University of Copenhagen, Denmark.
§From Copenhagen University Eyeclinic, Hvidovre hospital, Copenhagen, Denmark.
∥From the Center for Hospital Finance & Management, Department of Health Policy & Management, School of Public Health, Johns Hopkins University, Baltimore, Maryland.
This work was partially undertaken with a grant from the Agency for Healthcare Policy and Research (No. HS 07085). The Spanish team was additionally supported by grants of the Fondo de Investigación Sanitaria (FIS) (Expte. No. 95/0229) and the Agència d'Avaluació de Tecnologia Mèdica de Catalunya; the Danish team was additionally supported by the following foundations: Danish Eye Research the John & Birthe Meyer, and Denmark's Health, and by the Danish Medical Research Council.
Address correspondence to: Jordi Alonso, MD, PhD, Health Services Research Unit, IMIM, Carrer del Doctor Aiguader, 80.08003 Barcelona, Spain.