The Socioeconomics of Diabetic Retinopathy

Data from the United Kingdom quantify the societal burden of diabetic eye disease.

MONEESH PATEL, MBChB ∙ HEAN-CHOON CHEN, MBBS

Diabetes affects 5% of the world's population and its prevalence doubles every generation. The International Diabetes Federation estimates that in 2005 approximately 333 million people in the world aged 20 to 79 had diabetes. In the United Kingdom, with a population of over 60 million, more than two million people have been diagnosed with diabetes and an estimated 750,000 people have undiagnosed diabetes. In this population, more than 250,000 people have type 1 disease, while 1.8 million have type 2 diabetes, with the latter group making up about 90% of the population of patients with diabetes.^1,2

DIABETES IN THE UNITED KINGDOM

The UK prevalence figure for diabetes is predicted to reach three million by 2010. The incidence of type 1 diabetes in children is rising at a rate of 3% to 4% a year,³ while the increase in type 2 diabetes is closely linked to an aging population and rapidly rising numbers of obese or overweight people. Type 2 diabetes is also becoming increasingly common in the young in developed countries.

As well as being a major cause of vision loss in adults, diabetes is a leading cause of kidney failure and amputations. It is also a major risk factor for heart disease, stroke, and birth defects in children born to mothers with the disease. On average, life expectancy is reduced by 20 years in people with type 1 diabetes and by 10 years in people with type 2 diabetes. It is predicted that, in the next 10 years, there will be a 25% increase in the number of diabetes-related deaths.

Diabetic macular edema.

Access to good advice and effective health care is a priority for people who want to reduce these risks, including the threat to vision. Medical care aims to help reduce blood-sugar levels and blood pressure and to detect and treat complications at an early stage. Delays in diagnosing a person with diabetes, which can be as long as 12 years after the onset of the disease, mean that between one-third and one-half of patients with diabetes already have evidence of organ or tissue damage when diagnosed.

Individuals from disadvantaged sectors of society are considered to be at greater risk of developing type 2 diabetes and are more likely to experience complications from diabetes leading to higher rates of morbidity and mortality than those from more affluent sectors of society. The higher prevalence of diabetes in more disadvantaged areas could be attributable to a variety of factors that include obesity and physical inactivity, which are strong risk factors for type 2 diabetes and glucose intolerance.⁴ It is also known that people from lower socioeconomic backgrounds are less likely to attend for routine health checks, at which urine or blood glucose are measured.^5,6

THE COST OF MANAGING DIABETES MELLITUS AND ITS COMPLICATIONS

Diabetes has a high cost for individuals and the state. For individuals, there are both health and financial costs, with the latter comprising the cost of purchasing health care and the loss of earnings. Worldwide, it is estimated that the spending on diabetes mellitus and its complications totaled $232 billion in 2007, with more than 50% of this spent in the United States and 25% in Europe.

In the poorest nations of the world, type 1 diabetes is not infrequently a fatal disease because of the lack of access to insulin. With the increasing prevalence of the disease, the worldwide cost will rise due to increased health and social care costs, disability payments, and loss of income generation. In industrialized countries, the healthcare costs approximately break down into 25% for controlling blood sugar, 25% for managing long-term complications, and 50% for additional medical care associated with diabetes. This contrasts markedly with lower-income countries, where almost 100% of costs are associated with controlling blood sugar. In the United States, acute hospitalization accounts for 44% of the costs associated with diabetes, with 22% for outpatient care, 19% for drugs, and 15% for nursing care.⁵

In the United Kingdom, the Audit Commission estimates that 9% of all hospital costs (£1.9 billion) are attributable to diabetes, with additional costs in primary care. Results of the T2 ARDIS survey estimate £2.0 billion National Health Service (NHS) costs for caring for type 2 diabetes alone (4.7% NHS spend in 1998).⁷ Patients with diabetes consume a disproportionately high level of health resources. Although 2% to 3% of the UK population has diabetes, these people account for 10% of hospital admissions.

DIABETIC RETINOPATHY

Diabetic retinopathy (DR) is considered to be the leading cause of blindness in the working-age population in the developed world. It is particularly prevalent in the poor, the elderly, and in ethnic minorities who have greater difficulty accessing health care. In England, DR is the third most common cause of vision loss in adults, accounting for 5.9% of all severe visual-impairment registrations and is the fourth most common cause of partially sighted registrations, making up 7.4% of all such registrations.⁹

Some British studies have suggested that 5% to 10% of diabetic patients have sight-threatening retinopathy, with up to 40% of these patients having some degree of retinopathy at diagnosis.^10,11 The incidence of diabetic retinopathy increases with duration of disease; 90% of patients with type 1 diabetes and 60% of those with type 2 diabetes have some retinopathy 20 years after onset of disease. People with diabetes are 25 times more likely to suffer severe, permanent vision loss than people who do not have diabetes.¹²

Current management strategies emphasize screening and risk-factor reduction. The International Diabetes Federation guidelines state that, at a minimum, all people with diabetes should have annual direct fundoscopy and an examination of visual acuity by a trained provider, with more frequent screening for those with existing disease affecting vision or pregnancy.

Specialist training to detect the presence of DR is important, as the sensitivity of a primary provider with a standard ophthalmoscope is only 50%.¹³ If DR progresses despite risk-factor reduction, and vision becomes impaired or threatened, the proven therapy of choice is laser photocoagulation.¹⁴ The Disease Control Priorities Project has found annual screening and laser treatment to be relatively cost-effective, costing up to $700 per quality-adjusted life year in developing countries.¹⁵

Diabetic eye disease, like many diabetes-related chronic complications, attracts much greater prominence in wealthier countries, being largely overlooked in many developing countries. However, evidence indicates that populations in the latter countries will increasingly suffer from this disease over the next two decades, where up to 80% of the worldwide population of diabetic patients will be based. It is, however, a largely preventable cause of vision loss that can be controlled through cost-effective interventions, but many less wealthy nations lack adequate healthcare infrastructures to manage diabetes mellitus and its many complications. Success in reducing this growing threat to sight will be contingent on better research, attention to cultural implications, increased access to health resources, and improved health systems.

WHAT IS THE COST OF VISION LOSS?

The cost to the state of a person with permanent vision loss will vary according to many factors, including the age of the person, the provisions the state provides for a blind person, and also what is used as the definition of blindness. A commonly applied definition of blindness is 20/200 or worse in the better-seeing eye. Table 1 summarizes data available from various studies estimating the cost of vision loss from age-related macular degeneration and DR.¹⁶

The Cost of Blindness Report 2003 stated that the total annual costs for England for those registered as blind or partially sighted range from £1.4 billion to £2.9 billion, calculated from social benefit costs and loss of productivity, excluding direct treatment costs.²⁴ The actual numbers of blind and vision-impaired people may, however, be three times higher than those on the official Register with possibly 920,000 blind or visually impaired people in England and the annual cost to the state being as high as £8.8 billion. Meads and Hyde presented a similar figure in their 2003 study, with an annual cost to the UK government calculated to be up to £6455 per person; almost 50% of these costs represented loss of productivity.¹⁶ As diabetic retinopathy affects a proportionately greater number of working-age people, the cost to society of a person permanently vision-impaired from DR is likely to be higher than some other conditions.

More recent data for 2008 state the economic costs of partial sight and blindness on the United Kingdom total £22 billion, with direct healthcare costs amounting to £2.14 billion. This research estimated that there were a total of 1.8 million people with partial sight and blindness in the UK adult population in 2008, with 3.5% from diabetic retinopathy.²⁵

Early detection and treatment of DR could potentially avoid or reduce these costs; it is the stated aim of the English National Diabetic Retinopathy Screening Committee to reduce blindness from DR by 10% within five years of the launch of its program in 2006. Currently, there are approximately 9000 patients registered blind per year, secondary to DR, in England. In the United States, screening and treatment of eye disease in patients with diabetes mellitus costs $3190 per quality-adjusted life-year (QALY) saved. This cost is a weighted average (based on prevalence of different subtypes diabetic patients) of the cost-effectiveness of detecting and treating diabetic eye disease in those with insulin-dependent diabetes mellitus ($1996 per QALY), those with non–insulin-dependent diabetes mellitus (NIDDM) who use insulin for glycemic control ($2933 per QALY), and those with NIDDM who do not use insulin for glycemic control ($3530 per QALY).²⁶

In the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), 3.6% of younger-onset patients and 1.6% of older-onset patients (aged ≥30 years at diagnosis, an operational definition of type 2 diabetes) were legally blind at the end of the study²⁷ In the younger-onset group, 86% of blindness was attributable to DR and in the older-onset group, one-third of the cases of legal blindness were due to DR.

The 25-year WESDR follow-up data showed an increased risk of incidence of proliferative DR with higher glycosylated haemoglobin, higher systolic blood pressure, proteinuria, greater body mass index at baseline, and an increase in the glycosylated haemoglobin between the baseline and four-year examinations.²⁸ The incidence of macular edema was associated with male sex, more severe diabetic retinopathy, higher glycosylated haemoglobin, proteinuria, higher systolic and diastolic blood pressure, and more pack-years of smoking.²⁹

The Diabetic Retinopathy Study (DRS) and Early Treatment of Diabetic Retinopathy Study (ETDRS) have demonstrated the efficacy of laser treatment in DR. A more recent study compared two laser photocoagulation techniques for the treatment of diabetic macular edema: the modified ETDRS direct/grid photocoagulation technique and a potentially milder (but potentially more extensive) Mild Macular Grid (MMG). At 12 months after treatment, the MMG technique was less effective at reducing retinal thickening, as measured with optical coherence tomography, than the ETDRS laser photocoagulation approach. However, the visual acuity outcome with both approaches is not substantially different.³⁰

CONCLUSION

The gradient between health and socioeconomic status is well established,^31,32 and it may be perceived that, for those with diabetes, the gradient would be even more pronounced because of the chronicity of the many potential complications, which have both mortal and morbid consequences.³³ However, the picture is not clear. Many studies have demonstrated that, while there have been significant improvements in the treatment of diabetes in the last decade, patients from socioeconomically underprivileged sections of society have benefited less than their more affluent counterparts.^34-39

However, the results of research are inconsistent.⁴⁰ One study reports that across a sample of more than 29,000 individuals with type 2 diabetes whose mortality in relation to their social differences were documented, no significant differences were found among the women with diabetes.⁴¹ Mortality for the men was slightly increased for those less educated, but the gradient was less steep than for the non-diabetic population. Other studies have also reported conflicting results.^42,43

Within any one society, the mechanisms by which socioeconomic disadvantage translates into worse clinical outcomes are unclear but may relate to access to healthcare provisions, education (and understanding of diabetes and its myriad complications), compliance with treatment regimens, and patient participation in self-management. Improved (and more universal) healthcare provisions, targeted healthcare provisions to greater uptake of services, improved education of patients, and the availability of effective therapies may serve to attenuate the relationship between socioeconomic status and diabetes morbidity/ mortality. It is important that there is an improved understanding of the relationship between socioeconomic disadvantage, provision of health care, and outcomes in diabetes in order that stretched healthcare resources are most effectively utilized. RP

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