DIABETIC-RETINOPATHY - SCREENING AND PREVENTION OF BLINDNESS - A DOCTORAL THESIS

Diabetic eye disease is a major cause of blindness in the Western Worl d and remains one of the most serious complications of diabetes mellit us Retinopathy is the ocular complication of diabetes that most often leads to impaired vision. In recent years laser treatment has been int roduced that can significantly decrease the likelihood of blindness in diabetic patients, if the eyes are treated at the appropriate stage o f the disease. It remains a public health problem to make sure that ea ch patient is treated at the optimal time in the development of the ey e disease. Several types of screening programs have been designed thro ughout the world to meet this problem. We now report on our active scr eening program for diabetic eye disease and describe the sight and eye condition of the diabetic patients who have been involved in this pro gram. In 1980, regular eye screening for diabetic retinopathy was init iated at Department of Ophthalmology, Landakot Hospital. The number of diabetic patients seen regularly has increased considerably since the n, with 70-80% of type 1 diabetic patients in the country participatin g in the program in 1990, increasing to over 90% in 1994. About a fift h of type 2 diabetics in the country participated in the program in 19 90. The patients have undergone annual eye examinations and fundus pho tography. Laser treatment is administered for proliferative retinopath y and diabetic macular edema according to the Diabetic Retinopathy Stu dy and Early Treatment Diabetic Retinopathy Study criteria. In 1990, w e embarked on a cross-sectional study to evaluate the prevalence of re tinopathy and visual impairment of the type 1 and type 2 patients part icipating in our program. At the time of study, 205 insulin-taking pat ients, with age at diagnosis of less than 30 years participated in our screening program. Out of those, retinopathy was present in 106 (52%) patients, proliferative retinopathy in 26 (13%) and macular edema in 19 (9%). Visual acuity of 196 patients (96%) was equal or better than 6/12 in their better eye, 6 patients (3%) had 6/18 - 6/36 in their bet ter eye, and 2 patients (1%) had equal or worse than 6/60 in their bet ter eye, or legally blind. We concluded that the prevalence of retinop athy and visual impairment in type 1 diabetic patients in the country was low compared with other countries. In 1990, out of 245 diabetic pa tients with Type 2 diabetes, retinopathy was present in 100 patients ( 41%), proliferative retinopathy had been present in 17 (7%) and 24 (10 %) had diabetic macular edema. A total of 224 patients (91%) had visua l acuity equal or better than 6/12 in their better eye, 17 patients (7 %) with 6/18-6/36 in their better eye, and 4 patients (1.6%) equal or worse than 6/60 in their better eye, or legally blind. We concluded th at the prevalence of visual impairment of those type 2 diabetic patien ts participating in our screening program at the time of study was low compared with population-based studies from other countries. In 1992 we examined ways to make the screening program more efficient by ident ifying subgroups at low risk for developing eye disease that required treatment and therefore needed less frequent screening. We studied whe ther diabetic eye disease screening programs could be trimmed by exclu ding children and examining diabetic patients without retinopathy ever y other year. We examined all children under the age of 15 at the time of study and went through the files of all patients under age 15 exam ined from 1980 to 1992 at our diabetic eye screening program. We also followed for two years the type 1 and type 2 diabetic patients found t o have no retinopathy in 1990, establishing their retinopathy stage tw o years later. Our results indicated that diabetic children under the age of 12 do not need regular screening for eye disease. Biannual exam inations seemed to suffice in type 1 and 2 diabetic patients without r etinopathy. However, in a setting where the eye clinic is located apar t from the diabetic clinics, examinations every other year present pra ctical problems which may result in a less effective screening for dia betic eye disease. In 1994, the four-year incidence of diabetic retino pathy and visual impairment in the type 1 diabetic patients participat ing in the study in 1990 was established to elucidate whether the scre ening program was also associated with a low incidence of blindness in type 1 diabetic patients. Out of 205 patients participating at baseli ne, 175 patients (85%) participated over the full four-year period. Th e 4-year incidence of any retinopathy was 38%, of proliferative retino pathy 7%, and of macular edema 3%. Out of 174 patients, 7% showed impr ovement in visual acuity of 2 Snellen lines while 3% experienced worse ning of visual acuity of 2 Snellen lines during the four-year period. No diabetic suffered more than 2 lines deterioration of vision and no- one went legally blind. The incidence of retinopathy in Icelandic type 1 diabetics participating in our annual eye screening program was low and the visual acuity stable. During the period from 1979-1994 the pe rcentage of registered legally blind in Iceland, who were blind out of diabetic retinopathy, decreased from 2.4% to 0.5%, which is statistic ally significant. Our results suggested that visual impairment in diab etics can be prevented with active regular screening and timely laser therapy when needed. Also, excellent general diabetes care for diabeti c patients in Iceland may play a part in the low incidence of retinopa thy and visual impairment of type 1 diabetic patients in the country. In our diabetic eye screening program, each eye examination is followe d by fundus photography. Accordingly, retinopathy stage can be followe d photographically over several years. From vessel measurements of pho tographs taken of patients with diabetic macular edema participating i n the screening program, it was demonstrated that macular vessels cons trict after macular laser treatment. We conducted a study to assess wh ether excessive dilatation in diameter and elongation of retinal vesse ls occurred in the development of diabetic macular edema, supporting a hypothesis that the development of diabetic macular edema could be li nked to hydrostatic pressure changes described in Starling's law. From fundus photographs of diabetic patients attending our regular eye scr eening program, we measured the diameter and segment length of retinal vessels in 36 patients in 3 retinopathy groups (12 patients