Quality of Life Assessment in Diabetic Patients

IRENE A BARBAZETTO, MD, & HOWARD F FINE, MD, MHSc

INTRODUCTION

Vision impairment due to diabetic retinopathy (DR) and other eye diseases is associated with a significant decrease across all domains of quality of life (QoL). It has an impact comparable to that of major medical conditions. Although the direct physical impairment may be minor, the effect on the patient's psychological well-being can be severe and the reduction of independence is often overlooked when assessing disability.¹

Increasingly, researchers and clinicians are trying to quantify the impact of DR and its treatments on patients' QoL. The measurement of patient-reported health outcomes is a discipline aimed at exploring the effect of disease on QoL from the patient's perspective.² Health-related quality of life (HRQoL) is how people's own health affects their satisfaction with and enjoyment of living, including physical, psychological, and social functioning. HRQoL offers information that is complementary to other biophysical measures in evaluating the impact of disease on a patient and may aid not only in optimizing patient care but also in allowing one to analyze the cost-effectiveness of various treatments.

HEALTH RELATED QUALITY OF LIFE

Studies commonly measure HRQoL by means of utility value. Utility theory in health care sprang from economic theories introduced by von Neumann and Morgenstern³ in 1944 to deal with quantification of uncertainty and was later modified by Weinstein and Sasson⁴ in the 1970s to facilitate cost-effectiveness analysis in health care. A utility value of 1 is defined as perfect health and 0 as death. Disease states fall somewhere between 0 and 1. Several methods exist to measure health state preferences. Four methods more commonly used are standard gamble, time trade-off, willingness to pay, and rating scale methods.⁵

The standard-gamble method asks patients how willing they would be to risk a worse health state in hopes of achieving an improved health state. The time trade-off method asks how much life expectancy in years they would give up for a better health state. The willingness-to-pay technique asks subjects to evaluate their health state in monetary terms. Rating-scale methods offer them graphical or numeric scales on which to rate their health state.

HRQOL FOR VISUAL DISORDERS

Utility values in ophthalmology are usually highly correlated with the acuity of the better-seeing eye. Several vision-specific HRQoL measures have been introduced over the years. Commonly used tests include the Visual Functioning Index (VF-14) and the National Eye Institute Visual Function Questionnaire (NEI-VFQ) and its variations.

The VF-14 is a functional assessment consisting of
14 questions designed to elicit how patients function with their current vision. Here is an example of one question:

K Do you have any difficulty, even with glasses:

A Reading small print such as labels on medicine bottles, a telephone book, food labels?

A Writing checks or filling out forms?

Respondents who answer affirmatively must then rate the difficulty as "little," "moderate," "a great deal," or "unable to do the activity." The VF-14 was validated for patients with retinal disease in 1999.⁶ It addresses functional limitations but does not specifically elicit how visual decline affects patients' overall sense of well-being.

The NEI-VFQ investigates visual/functional limitations and how they have an impact on a patient's overall social and emotional functioning. This 51-item metric was validated in 1998 on patients with cataract, macular degeneration, DR, glaucoma, cytomegalovirus retinitis, and low vision.⁷ The areas tested (number of questions) were: general health (2), general vision (2), ocular pain (2), near vision (7), distance vision (7), vision-specific social functioning (4), vision-specific mental health (8), expectations for visual function (3), vision-specific role functioning (5), dependency due to vision (5), driving (4), peripheral vision (1), and color vision (1). This comprehensive metric is commonly employed in large ophthalmic trials. A drawback is that questionnaires with numerous items can be unwieldy, time consuming, and expensive to administer.

Intending to streamline the NEI-VFQ, a shorter version with 25 items was validated in 2001, the 25-Item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25). It can be administered in 5 minutes.⁸ The Table shows a comparison of the questionnaires.

DIABETIC RETINOPATHY AND HRQOL

Brown and colleagues published a 1999 study exploring the general relationship between QoL and vision loss from DR using the time trade-off method. They found that the average person with 20/40 vision in the better-seeing eye was willing to trade 2 of every 10 years of life in return for perfect vision (utility value of 0.8), while the average person with counting fingers vision in the better eye was willing to trade approximately 5 of every 10 years (utility value of 0.52) in return for perfect vision.⁹ Subsequent analyses in DR patients not only confirmed these findings but also showed that these results were independent of gender, formal education, and duration of visual loss. Notably, the utility value in this study directly depended on the degree of visual loss due to the disease.¹⁰

Klein and colleagues examined the association of the NEI-VFQ-25 questionnaire and diabetes-related symptoms and comorbidities in patients with type 1 diabetes. In their study, lower total NEI-VFQ-25 scores were independently associated with poorer visual acuity (VA), more severe retinopathy, older age, a history of loss of tactile sensation, and more total pack-years of cigarettes smoked.¹¹ However, the association of lower scores in HRQoL tests with severe visual impairment is not specific for DR. When they were stratified for VA loss, DR and age-related macular degeneration seemed to have comparable visual utility scores.¹²

The assessment of QoL is test-dependent but is also affected by environmental and socioeconomic factors. For example, the loss of driving ability may have less impact in an environment with a supportive infrastructure. Using the RetDQoL test, a diabetic-specific 4-phase iterative approach incorporating qualitative and quantitative methods, European researchers demonstrated that, although many patients were able to cope with and adjust to the loss of driving, the concerns and worries of visual impairment due to diabetes had a significant impact on QoL.¹³

The impact of visual impairment is not only significant for QoL but also for life expectancy. A study by Knutdson and colleagues showed that persons with visual impairment from DR had greater mortality than persons without.¹⁴

HOW TREATMENTS AFFECT HRQOL

Changes in QoL after intervention for sight-threatening retinopathy have also been subject to investigation and the results to date have been somewhat controversial. Tranos and colleagues evaluated 55 patients before and
3 months after focal photocoagulation for diabetic maculopathy. Using the NEI-VFQ questionnaire, they found a significant improvement after treatment in QoL associated with many aspects of vision and vision-related functions, such as near and distance vision, vision-specific social functioning, vision-specific mental health, and expectations for visual function and dependency due to vision.¹⁵

Sharma and colleagues conducted a cost-effectiveness analysis for grid laser treatment for diabetic macular edema (Figure) based on the data of the ETDRS study group. In their analysis, patients with a 40-year life expectancy experienced an increase in QoL after laser treatment corresponding to an additional 3 months of life.¹⁶

More recently, Scanlon and colleagues evaluated 240 patients with DR before and 2 weeks after laser photocoagulation. They found a pronounced reduction of QoL after the first laser treatment but an improvement as patients progressed to receive multiple treatments. This may be explained by treatment-related diminution in visual field and from progression of disease. Many patients felt that their expectations were met, but the treatment had less of an impact than they had hoped for. Yet patients stated that they were willing to repeat laser treatment if needed.¹⁷

It should be kept in mind that poor vision often is correctable and visual recovery can reduce the risk for injury and improve the QoL for diabetics. A recent study by the Centers for Disease Control showed a prevalence of 7.2% of correctable visual impairment among US diabetics aged 20 years or older. The authors conclude that the proper prescription for glasses or contact lenses would have restored normal VA to 65.5% of visually impaired diabetics.¹⁸

OUTLOOK

To improve diabetic care and to serve patients better, ophthalmologists will need to pay more attention to the patient's perspective. Currently no data are available regarding QoL measures for surgical interventions, injections of triamcinolone or anti-VEGF substances, or the use of protein kinase C inhibitors. Detailed analysis could help not only to better address patients' expectations but also to provide more individualized treatments. In the future, newer and potentially less destructive treatments may aid us not only to better control patients' diseases but also to better address their specific needs and to improve their QoL. RP

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Irene A. Barbazetto, MD, and Howard F. Fine, MD, MHSc, are both ophthalmologists with the E.S. Harkness Eye Institute at Columbia Presbyterian Hospital in New York. Dr. Barbazetto can be reached at (212) 305-9535 or at ib206@columbia.edu. The authors have no financial interest in the topics discussed. This manuscript was supported by the Heed Ophthalmic Foundation.