Developing an Algorithm to Convert Routine Measures of Vision into Utility Values for Glaucoma

Abstract

Purpose: Measures of quality of life called utility values (UVs) are needed to deliver the most cost-effective health care for glaucoma patients. UVs are rarely measured in clinical research and practice whereas clinical outcomes such as visual field are routinely collected. The aim of this study was to develop an algorithm that calculates UVs directly from combinations of routine measures of binocular visual field, visual acuity, and contrast sensitivity.

Methods: A total of 132 outpatients with primary open angle glaucoma were recruited. The Time Trade-off (TTO) question was administered during face-to-face interviews. Binocular ETDRS logMAR visual acuity (VA_B), binocular Pelli-Robson contrast sensitivity (CS_B), and Humphrey 24-2 monocular visual field tests were performed on the same day. Integrated (binocular) visual field (IVF) scores were derived. Tobit regression analyses were used to model utility values based on combinations of IVF, VA_B, CS_B and other controlling factors.

Results: UVs recorded for 123 cases correlated significantly with both clinical measures of binocular visual function (r = −0.47, IVF; r = −0.48, VA_B; r = 0.50, CS_B; P <0.0001) and measures of vision-specific quality of life (r = 0.54–0.6, P <0.0001). Two final models incorporate terms for IVF and VA_B, with or without living arrangements, and explain 22% and 31% of variation in utilities. CS_B was not included in either model due to co-linearity between CS_B and VA_B confounding the models.

Conclusion: The models provide preliminary algorithms for predicting the expected UVs for glaucoma populations directly from clinical outcomes collected routinely in clinical practice.

Keywords::

• Glaucoma
• Quality of life
• Utility values
• Time trade-off
• Cost-utility

ACKNOWLEDGMENTS

The authors wish to thank all participants who took part in the study; Professor Jack Dowie, London School of Hygiene and Tropical Medicine, for his inspiration during the conception of the project; Dr Patricio Schlottman, Dr Rizwan Malik and other members of the Glaucoma Research Unit and the Research & Development Department of Moorfields Eye Hospital, for their supervision and support during data collection; and Professor Gary Rubin of the Institute of Ophthalmology for advice on methodology.

This study was supported by an Investigator Initiated Research Grant from Pfizer Inc, New York Headquarters (2005-0570), and a grant awarded by Moorfields Eye Hospital Special Trustees, London, UK.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the article.