Public Health Focus: Prevention of Blindness Associated with Diabetic Retinopathy

Each year in the United States, as many as 40,000 new cases of blindness occur among persons with diabetes (CDC, unpublished data, 1993). Diabetes is the leading cause of new blindness among U.S. adults aged 20-74 years (1). In addition, persons with diabetes are 25 times more likely than the general population to become blind. Most of this blindness in persons with diabetes results from diabetic retinopathy, a disorder characterized by microvascular changes and hemorrhage in the retina. Seven million persons in the United States have diabetes, and diabetic retinopathy will affect the majority during their lifetimes. This report summarizes information regarding the efficacy, effectiveness, and cost-effectiveness of screening for diabetic retinopathy.

The National Diabetes Data Group recognizes two major types of diabetes: insulin-dependent diabetes mellitus (IDDM) and noninsulin-dependent diabetes mellitus (NIDDM). Retinopathy occurs most frequently and severely among persons with IDDM (Figure 1), who represent approximately 5%-10% of all persons with diabetes (2). The prevalence of any diabetic retinopathy in this group is low immediately after diagnosis but increases to more than 90% after 15 years. The prevalence of proliferative diabetic retinopathy among persons with IDDM is negligible until 5 years' duration and increases to approximately 60% after 20 years. Among persons with IDDM, the prevalence of clinically significant macular edema (CSME) increases from less than 5% at short durations following diagnosis to more than 20% at 25 years' duration.

Approximately one third of all persons with NIDDM have insulin-treated diabetes. The prevalence of any retinopathy among persons with insulin-treated NIDDM steadily increases from 10%-30% at initial diagnosis to 90% at 25 years' duration (Figure 2); the prevalence of proliferative diabetic retinopathy increases from 2% at the time of diagnosis to approximately 20% after 20 years' duration. The prevalence of CSME is negligible at short durations following diagnosis but increases to more than 10% after 25 years.

Approximately half of all persons with diabetes have NIDDM treated by diet or oral hypoglycemic agents. The prevalence of any retinopathy among persons with non-insulin-treated NIDDM increases from 10%-20% at diagnosis to more than 60% at 20 years' duration. The prevalence of proliferative diabetic retinopathy increases from 2% at diagnosis to approximately 5% after 20 years' duration (Figure 2). The incidence and rate of progression of retinopathy are lowest among persons in this group. The prevalence of CSME in this group increases from less than 3% at short durations following diagnosis to more than 10% after 25 years. Efficacy/Effectiveness

Prospective clinical trials indicate that laser photocoagulation therapy is effective in reducing the risk of visual impairment (3,4). Panretinal laser photocoagulation can reduce the risk of severe visual loss by at least 60% in some persons with diabetes (5 ). An annual eye examination can identify diabetic retinopathy early and permit timely treatment to prevent loss of vision and possible blindness (6). However, about half of persons with diabetes had not had a dilated eye examination in the preceding year (7 ). Efficacy of Screening

The sensitivity of ophthalmoscopy in screening to identify diabetic retinopathy increases with the health-care provider's training and experience in performing eye examinations (8). Sensitivity of ophthalmoscopy performed by ophthalmologists, optometrists, trained ophthalmic technicians, and other health-care providers ranges from 50%-100% (9,10).

Retinal photography is a standard technique for examining eyes that have been pharmacologically (mydriatically) dilated or physiologically (nonmydriatically) dilated. Seven-field stereo retinal photography is both 100% sensitive and specific for diagnosing diabetic retinopathy and is the standard for evaluating severity of retinopathy in clinical trials and epidemiologic studies. Because stereo retinal photography is labor-intensive and expensive, other modes for screening have been tested and compared. Both mydriatic and nonmydriatic retinal photography, using wider angle lenses and fewer fields, have tested favorably. Cost-Effectiveness of Screening

For working-aged persons in the United States (i.e., persons aged 21-64 years), the federal budgetary cost of one person-year of blindness has been estimated at $11,896 (11 ). Economic evaluations indicate that screening for diabetic retinopathy costs less than the cost of one person-year of blindness. Findings from one study (12) indicate that biannual and annual screening programs for persons with IDDM and NIDDM are cost-effective. Specifically, this study evaluated the cost-effectiveness of annual or biannual screening using three different diagnostic strategies (i.e., ophthalmoscopy and retinal photography with and without dilation) (Table 1). Each of the six strategies was compared with the baseline costs and consequences of the natural disease progression. The impact of treatment with laser and vitrectomy was added to natural progression as part of the modeling. A limitation of this study was that the model did not include the incidental benefits of detecting and treating cataract, glaucoma, and macular edema.

A second study evaluated the cost-effectiveness of different screening protocols for diabetic retinopathy among persons with IDDM (13) and focused on the effectiveness of eye examinations at three (6-, 12-, and 24-month) intervals, with and without the performance of seven-field stereo retinal photography. Assumptions included a sight-year cost of $6300 (based on Social Security data), an annual cost of $3150 for sight loss associated with macular edema, and an average age at onset of 12.5 years. Based on these assumptions, and by varying the strategies, $62 million-$109 million and 71,000-85,000 sight-years would be saved annually in the United States.

Reported by: Div of Diabetes Translation, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: The findings in this report indicate that screening for diabetic retinopathy is both effective for preventing blindness and cost-effective. This prevention effort requires improvements in timeliness of screening, case-finding, and entry into the health-care system. To initiate treatment, all persons with diabetes (except those with IDDM of less than 5 years' duration) should receive an annual dilated eye examination performed by a trained provider and should receive appropriate referral and treatment.

To reduce blindness associated with diabetic retinopathy, public health and clinical health-care providers must identify and treat high-risk persons before loss of vision. Diabetes-control programs are effective in identifying and treating persons at high risk for vision loss (14). Tertiary prevention in the form of laser treatment for proliferative diabetic retinopathy and macular edema is available in all states and most areas. Ongoing investigations are assessing whether effective control of hyperglycemia will ensure secondary prevention of diabetic retinopathy and blindness.

References

1. National Society to Prevent Blindness. Visual problems in the U.S. data analysis definitions. Data Sources, Detailed Data Tables, Analysis, Interpretation. New York: National Society to Prevent Blindness, 1980:1-46.

2. Klein R, Klein BEK, Moss SE. The Wisconsin Epidemiological Study of Diabetic Retinopathy: a review. Diabetes Metab Rev 1989;5:5559-

4. Diabetic Retinopathy Study Research Group. Photocoagulation treatment of proliferative diabetic retinopathy: clinical application of Diabetic Retinopathy Study (DRS) findings, DRS report no. 8. Ophthalmology 1981;88:583-600.

5. Early Treatment Diabetic Retinopathy Study Research Group. Treatment techniques and clinical guidelines for photocoagulation of diabetic macular edema. Ophthalmology 1987; 94:761-74.

6. Ferris FL. How effective are treatments for diabetic retinopathy? JAMA 1993;269:1290-1.

7. CDC. The prevention and treatment of complications of diabetes mellitus: a guide for primary care practitioners. Atlanta: US Department of Health and Human Services, Public Health Service, 1991.

8. Brechner RJ, Harris M, Cowie K. Eyes and diabetes -- who's getting care? The National Health Interview Survey Diabetes Supplement 1989. Diabetes 1992;41(suppl 1):7A.

9. Singer DE, Nathan DM, Fogel HA, Schachat AP. Screening for diabetic retinopathy. Ann Intern Med 1992;116:660-771.

10. Nathan DM, Fogel HA, Godine JE. Role of diabetologist in evaluating diabetic retinopathy. Diabetes Care 1991;14:26-33.

11. Moss SE, Klein R, Kessler SD, Richie KA. Comparison between ophthalmoscopy and fundus photography in determining severity of diabetic retinopathy. Ophthalmology 1985;92:62-7.

12. Chiang YP, Bassi LJ, Javitt JC. Federal budgetary costs of blindness. Millbank Quarterly 1990;70:319-40.

13. Dasbach EJ, Fryback DG, Newcomb PA, Klein R, Klein BEK. Cost-effectiveness strategies for detecting diabetic retinopathy. Med Care 1991;29:20-38.

14. Javitt JC, Canner JK, Frank RG, Steinwachs DM, Sommer A. Detecting and treating retinopathy in patients with type 1 diabetes mellitus. Ophthalmology 1990;97:483-95.

15. Will JC, German RR, Michael S, Durth D. Compliance in eye disease screening programs. Diabetes 1991;40(suppl 1):351A.

    
    
    

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