Secondary prevention in diabetes mellitus

THE PAPER by Bennett and Knowler is concerned in the main with primary prevention of diabetes. The comments in this discussion will reflect another traditional public health concern, that is, the role of secondary prevention in this disease. Is there a need for screening or examining in a systematic fashion those persons known to have diabetes to determine whether more preventive or therapeutic efforts would benefit this high risk population? I will limit my discussion of this question to the eye and visual function in diabetic persons. Diabetes is a major cause of blindness in the United States and has been estimated to account for 5000 new cases each year [l]. The adverse effects of diabetes on the visual system may occur through several different pathways. Retinopathy is the pathologic process which is most commonly thought to occur in eyes of diabetic persons. In 1979-1980 the Wisconsin Epidemiologic Study of Diabetic Retinopathy was undertaken. That study was designed to determine the prevalence and severity of retinopathy in diabetic persons who received primary medical care in an eleven county area (Health Service Area 1) in southern Wisconsin [2]. All persons whose age at onset of diabetes was less than 30 years and who were taking insulin were examined; these persons have been referred to as the “younger onset” group. A stratified sample of persons who were diagnosed after 30 years of age was also examined; these persons have been referred as the “older onset” group. The population has been described in detail in other reports [3-51. Rates of legal blindness, that is, visual acuity of 20/200 or worse in the better eye may be compared with rates reported from the Framingham Eye Study, and from the Health and Nutrition Examination survey. Rates of legal blindness increased with increasing age in all groups. The rates in the diabetic persons were much higher at each age. In the younger onset persons, the overall rate of legal blindness was 3.6%; about 86% of the cases were attributable to diabetic retinopathy. In the older onset persons, the rate of blindness was 1.6x, and 33% of the cases were caused by diabetic retinopathy [6]. Davidson has cited rates of complications in diabetic patients. Rates of retinopathy, proteinuria, neovascularization, azotemia, blindness, and atherosclerosis all increased in frequency as the number of years of diabetes increased. Retinopathy occurred relatively early in the disease, and was the most frequent of these complications. More than 70% of patients had evidence of retinopathy after 25 years of the disease [7]. There are other recent sources of data that have been used to estimate the rates and severity of retinopathy in diabetic persons. Frank er al. [S] and Palmberg et al. [9] described the experience from their clinic practices in which they examined insulin dependent diabetic patients. Frank et al. reported no cases of retinopathy in 60 patients who had had diabetes for &4 years; Palmberg et al. found no cases in 80 patients who had &3 years of disease, but found 21% when he saw the same group again at 4-5 years. In the Wisconsin population, Klein et al. reported that in younger onset persons with from 0 to 4 years of diabetes, 13.6% had retinopathy [4].