Epidemiology of Ocular Functions and Diseases in Persons With Diabetes

Visual impairment (visual acuity poorer than 20/40) in those with type 2 diabetes was estimated to affect 937,000 Americans age ≥40 years in data collected in the 1990s. While data from the National Health and Nutrition Examination Surveys collected in 1999–2004 and 2005–2008 suggest that this prevalence is declining, the prevalence of visual impairment is about two to three times as high in persons with diabetes as in those without the disease. Prevalence estimates for those with type 1 diabetes suggest that they too have a disproportionate prevalence of visual impairment compared to those without diabetes. Diabetic retinopathy is one of the five most common causes of severe visual impairment (visual acuity of 20/200 or worse) in the U.S. population. There are important differences in the distribution of low vision (best-corrected visual acuity of <20/40 in the better eye, excluding those who were blind) attributable to diabetic retinopathy by racial/ethnic group with 4.9%, 14.5%, and 13.0% of whites, blacks, and Hispanics, respectively, being affected. For blindness (best corrected visual acuity <20/200 in the better seeing eye), the corresponding prevalences are 5.4%, 7.3%, and 14.3% for the three races/ethnicities. The risk of visual impairment increases with increasing duration of diabetes for both type 1 and type 2 diabetes. Among risk factors that affect vision in persons with diabetes, the level of glycemia is the most important. In prevalence data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) for persons with type 1 diabetes, those in the highest quartile of glycosylated hemoglobin (A1c) were about four times as likely to experience doubling of the visual angle (a loss of 15 or more letters on the LogMar Chart, e.g., a change in visual acuity in the better eye of 20/20 to 20/40 or 20/30 to 20/60 or worse) over 10 years as those with A1c in the lowest quartile. For those with type 2 diabetes, the effect across quartiles was about 1.5 times. Fortunately, treatments are available for some specific ocular complications that have a direct effect on visual acuity. The decreased visual acuity that is the most important functional effect of diabetes on the eye is largely attributable to anatomic pathologic conditions, such as diabetic retinopathy, diabetic macular edema, cataract, glaucoma, and corneal disease. Of these, the most important, due to the chance of permanent decreased vision, are severe diabetic retinopathy (i.e., proliferative diabetic retinopathy [PDR]) and diabetic macular edema. In the WESDR, a largely white cohort, 71% of persons with type 1 diabetes and 47% of persons with type 2 diabetes had retinopathy, 23% and 6% had PDR, and 11% and 8%, respectively, had macular edema at the baseline examination (1980–1982). Risk factors for development and progression of diabetic retinopathy and incidence of PDR include longer duration of diabetes, higher level of glycemia, greater body mass index, higher blood pressure, and the presence of nephropathy. Hispanics and blacks have higher prevalences of retinopathy compared to whites due, at least in part, to differences in health care access. Panretinal photocoagulation for treatment of PDR and focal and grid laser photocoagulation for clinically significant macular edema (CSME) have reduced the risk of severe vision loss by as much as 90%. Intravitreal injections of anti-vascular endothelial growth factor for CSME have shown efficacy in randomized controlled clinical trials in diminishing the effects of these retinal complications on vision and are expected to result in further prevention of visual loss. However, these treatments are expensive and associated with the risk of complications. While the prevalence of severe diabetic retinopathy is likely to be somewhat lower currently than in the past, evidence from cohorts defined in the early years of the 21st century suggests that this condition has not been overcome, and with the likely increases in the number of youths and adults with type 2 diabetes, diabetic retinal outcomes will continue to be important health burdens. Vision loss associated with diabetic retinopathy has been associated with poorer health-related quality of life. Guidelines for screening for PDR and macular edema have been developed. Studies have shown the efficacy and cost-effectiveness of such screening, yet some groups, such as Hispanics, are not getting timely dilated eye examinations as recommended in the guidelines. Aside from aging, diabetes is the most common risk factor for cataract. Cataract surgery with implant of artificial intra-ocular lenses is highly successful in restoring vision when cataract is the primary reason for decreased vision in those with diabetes. However, the surgery can have side effects or complications inherent in intra-ocular surgery that are more common in those with diabetes than in those without it. In addition, cataract surgery is a major health care cost because of its frequency, and when resources are scarce, surgery may be delayed, prolonging the time and inconvenience of decreased vision associated with cataracts. The need for surveillance and care for those with diabetic ocular complications is likely to increase with the projected increase in the number of people with diabetes. In addition, changes in therapy, both general medical and specific ocular, are changing care patterns. Therefore, to anticipate health care needs and costs, and as part of a comprehensive public health program to diminish the disabilities associated with ocular problems related to diabetes, ongoing collection of population-based data on this subject is needed.