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Editors Selection IGR 14-2
Health and Quality of Life: Impact of VF loss on QoL
Comment by Paul Healey on:
21402 Impact of visual field loss on health-related quality of life in glaucoma: The Los Angeles Latino Eye Study, McKean-Cowdin R; Wang Y; Wu J et al., Ophthalmology, 2008; 115: 941-948
How do people go blind from glaucoma? As students we are told glaucoma is a generally asymptomatic disease. Yet it is the most common cause of irreversible blindness worldwide. The idea that patients with glaucoma have 'normal' vision and quality of life right up until they become blind is commonplace. Health economists refer to it as 'falling off the cliff'. It makes it very difficult to work out the benefits of diagnosis and treatment. For most of course of the disease there is no benefit because there is no loss of quality of life. At the end stage there is no benefit because there is no treatment that can restore the quality of life so devastatingly lost. When assessing loss of quality of life, health economists have another problem. Telling someone they have a disease will itself cause a loss of quality of life. Measuring quality of life in people who do not know they have a disease is difficult. McKean-Cowdin et al. (484) provide new and important data from the Los Angeles Latino Eye Study suggesting our concept of 'normal' glaucoma patients is false. The authors measured Health-related Quality of Life in LALES participants with the well established NEI-VFQ-25 and SF-12 questionnaires. They found that Quality of Life measured by the VFQ-25 and the physical component of the SF-12 was lower in participants with glaucoma compared to those without. This finding persisted in the 75% of cases who did not know they had glaucoma when they answered the questionnaires, suggesting it was indeed a disease effect. The key areas of loss of quality of life were in vision-related role function, driving difficulties, vision-related dependency and peripheral vision. Among participants with glaucoma, quality of life was worse in those with any visual field loss. Location of visual field loss was also important with large effects found in those with central and bilateral peripheral field loss compared to no visual field loss. For unilateral peripheral field loss, effect sizes were small to moderate.
Telling someone they have a disease will itself cause a loss of quality of lifeThe last and most important finding was a consistent drop in VFQ scores with decreasing visual field mean deviation in either the better eye or the summated binocular visual field of participants with glaucoma. The loss of quality of life was linear from an MD of 0Db down to -30db. For the composite VFQ, 1.3 units of quality of life were lost per dB drop in visual field MD. For the VFQ driving score, 2.3 units were lost per dB. When combined with cohort data from other studies suggesting the average glaucoma patient loses about 1dB in MD per year, these data finally allow us to estimate lifetime loss of quality of life in glaucoma. The fact that this loss occurs throughout the range of MD suggests that loss of quality of life in glaucoma occurs at all stages, not just in advanced disease. As long as confounders such as cataract can be excluded, these findings should cause us to reconsider the effects of early and moderate glaucoma on our patients' health and our interventions to improve it.
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