March 1991, Volume 41, Issue 3

Original Article

PREVALENCE OF DIABETIC RETINOPATHY IN PAKISTANI SUBJECTS A PILOT STUDY

Akhtar Jamal Khan  ( Akhtar`s Eye Hospital, Rashid Minhas Road, Gulshan-e-Iqbal, Karachi. )

ABSTRACT

Of 3000 diabetic patients screened, 780 were diagnosed to have retinopathy. The incidence of the complication was higher in the age group of 51 years and above, and of diabetes (76.7%) (JPMA 41: 49, 1991).

INTRODUCTION

The average life of diabetic patients has been prolonged with the advent of antidiabetic drugs. Unfor­tunately, the incidence of diabetic retinopathy has increased many folds. In a nonselective randomized population based study in 1959 at Liaquat Medical College, Hyderabad, the incidence of diabetes was 1.7% in patients below 40 and 3% in above 40 years age group1. In another survey at Karachi in 1986, it increased to 7.66%1. The present study was conducted to determine the incidence of retinopathy both proliferative and back­ground type, and see the effect of the duration of diabetes on the patients.

PATIENTS AND METHODS

An IBM personal computer was used to compile the data of 3,000 diabetic patients examined. Ml patients underwent a prdiminary examination, including exter¬nal ocular tests, recording of visual acuity and the best corrected visual acuity. Intraocular pressure was recorded by applanation tonometry. Fundus examina¬tions by indirect ophthalmoscope as well as with slit lamp and fundus lens were done routinely. For per¬manent record, coloured photographs by Topcon Fun¬dus Camera were taken in all cases where changes due to diabetes were noted either in the anterior or posterior segment. Fluorescein angiography was carried out only for macular oedema. Diabetic retinopathy was further classified into background type of diabetic retinopathy (BDR) and proliferative diabetic retinopathy (PDR).

RESULTS

Three thousand diabetics were included in the study of which 780 (26%) had retinopathy. Four hundred and nine (52%) were males and 371 (48%) females. Six hundred and seventeen (79%) cases had background, and 163 (2 1%) proliferative retinopathy. Of the 409 male diabetics the incidence of it increased alarmingly with the prolongation of the duration  retinopathy rose from 0.7% in the 2 1-30 year age group to 66.1% in the age group 51 years and above while the incidence in the female population was 1.1% in the age group 21-30 years and 54.2% in the age group of 51 years onward (Table I).

A remarkable correlation was observed between the duration of diabetes and retinopathy. Of 780 patients with retinopathy 182 (23.3%) had diabetes for 1-5 years and 598 (76.7%) for 6-16 years. The effect of duration of diabetes on the development of retinopathy is similar in both sexes (Table II).

DISCUSSION

The two common hypotheses for pathogenesis of diabetic retinopathy are (i) high blood pressure and low intraocular pressure (I.O.P) 3 and (ii) hypoxia leading to production of vasoproliferative substances4,5 ­Stefansson et al3 observed that high blood pressure and low I.O. P. were present in a majority of their patients with diabetic retinopathy. In contrast those diabetics, who had low blood pressure and high intraocular pressure, did not develop diabetic retinopathy. The auther also observed that if the diabetic patients who had low blood pressure with diabetic retinopathy, developed glaucoma, the progress of diabetic retinopathy was retarded or stopped. Therefore, they opined that high blood pressure and low intraocular pressure were the main causes of diabetic retinopathy, rather than hypoxic retina, as suggested by others4-7. The initial changes in the capillary cell population, which include endothelial proliferation on the venous side and generalized pericyte damage, are possibly related to the capillary venous dilation linked with the initial increase in blood flow8. The first sign of diabetic retinopathy is therefore an increased permeability to fluorescein dye as measured by fluorophotometer9-12. In diabetics there is an increase in hemoglobin A1c and decrease in 2-3 diphosphoglycerate (2-3 DPG) which increases the affinity of Hb for oxygen. Thus oxygen release is affected. The total oxygen consumption of the diabetic retinaincreases by 10-12% above the normal13,14, so it is believed that these two factors, i.e. increased consumption and decreased availability of oxygen, lead to tissue hypoxia state. Constant high blood pressure, prolonged hyper­glycaemia, increased Hb Aic and decreased 2-3 DPG cause hindrance in dissociation of oxygen, from Jib molecule and on the other hand increased consumption of oxygen by diabetic retina causes an imbalance be­tween supply and demand. This probably leads to venous capillary dilation surrounded by capillary closure. Another factor which plays an important role in the pathogenesis of loss of retinal pericytes and thickening of basement membrane is aldose reductase15. Hohman16 grew human retinal capillary pericytes in tissue culture and demonstrated presence of aldose reductase in these pericytes. In various population based studies conducted in different parts of the world, including Australia17,18, Denmark19, Iceland20 and United States21 it was estab­lished that the prevalence of diabetic retinopathy varies between 24 and 70%. However the reason for large variations in the prevalence of total (24% to 70%) and proliferative (4.5% to 22%) retinopathy, may be due to the fact that these studies were not performed under the same conditions22 (Table III). According to a study conducted in Sweden24. the prevalence of retinopathy in insulin-treated diabetics of  40 years of age or younger was 66% and in orally treated diabetic patients of all ages it was 17%. There was an increasing prevalence of retinopathy in all age groups with longer duration of diabetes. Background retinopathy was present in 31% subjects and proliferative in 13%.22. The results of our study are comparable to the figures quoted by other investigators. A higher age group and a long duration of diabetes influence the develop­ment of the retinal changes. The pathogenesis is yet to be determined.

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