Overall design
The study was part of a general cross-sectional survey of DM patients carried out to assess and establish the prevalence of DM complications including retinopathy among diabetic patients in Al-Ain District, UAE during 2003/2004.
Subjects and setting
Multi-stage random sampling was used to select 8 primary health care centers (PHC) in Al-Ain district (out of 22 rural and urban health care centers) in addition to two diabetic clinics in the only two governmental hospitals in the district (Tawam and Al-Ain hospitals). Thus, our sampling frame included all UAE national and non-national DM patients (types 1 and 2) of all ages of both genders, attending any of the selected primary health care centers (PHC) for any reason and diabetic clinics at the two hospitals for follow up. Within these primary sampling units (PHC and hospital clinics), a systematic random sampling was carried out to select a sub-sample of patients to be approached for participation in the study. In the absence of a computerized database in the UAE every third diabetic patient was approached to participate during the study period. A sample size of 625 was calculated to give a standard error in the prevalence of retinopathy of less than 2%. In total 600 patients were contacted by general practitioners and diabetologists, out of which, 513 patients (86%) agreed to enroll. The study was approved by the ethical committee of the Faculty of Medicine and Health Sciences of the UAE University.
Data collection
After receiving informed consent, known diabetic patients in Al-Ain were interviewed by the treating doctors at PHC and hospital clinics and information pertinent to their DM type, duration, compliance with treatment as assessed by doctors, associated complications and co-morbidity was collected. Additionally, blood pressure was measured by the PHC/hospital nurse early in the morning and prior to drawing blood samples in the sitting position, using a standard mercury sphygmomanometer. Height was measured without shoes, and weight recorded while wearing indoor clothing. Body mass index (BMI) (weight in Kg, divided by height in meters squared) was calculated. The WHO (1977, 1979) classification for BMI was used to estimate the degree of obesity [10]. Fasting blood samples were taken to assess lipid profile, blood sugar and glycated hemoglobin (HbA1C) levels. Total lipid profile (total cholesterol (TC), high density lipoprotein (HDL), TC/HDL Ratio, low density lipoprotein (LDL) and triglycerides) were measured by a capillary tube whole blood method using the Cholesterol LDX lipid analyzer. Dyslipidaemia was taken to be present when the total cholesterol was > 5.60 mmol/L and/or triglycerides > 2.10 mmol/L, LDL > 3.4 mmol/L, and or HDL < 0.91 mmol/L [11]. Glycated hemoglobin (HbA1C) was measured using the Bayer DCA 2000+ analyzer and a value of less than 7% was taken to indicate good glycemic control. A standard 12- lead electrocardiogram (ECG) was recorded for all patients. The WHO definition of hypertension was used in this study: systolic blood pressure 160 mmHg or more and/or a diastolic blood pressure 95 mmHg or more, or on going treatment with antihypertensive drugs. MA was assessed using semi-quantitative dry immuno chemical screening strips (Micral 11 ® test strips (Roche diagnostic GmbH Mannheim Germany). Micral Tests were performed on first morning urine sample collections and a value of more than 20 μg/min was judged as pathological.
All patients were referred to two ophthalmologists working at the two main hospitals of Al-Ain district and underwent detailed eye examination. After adequate mydriasis, the examination of the interior segment was carried out using Haag Streit slit lamp 900BQ with stereovariator. The intraocular pressure was measured using applanation tonometry. Fundus photography operating with a digital camera (Super 66 equipped with stereo fundus lens).
Diabetic retinopathy was classified using Watkins et al (2003) standards, and as follows: i) background retinopathy, if microaneurysms, haemorrhages (dot, blot or flamed shaped) or hard exudates and/or macular edema were present; ii) proliferative diabetic retinopathy, if cotton wool spots, multiple large blot haemorrhage, neovascularisation of the retina or iris, angle, venous beading, loops, and reduplication, arterial sheathing or atrophic looking retina were present; and iii) advanced diabetic eye disease, if vitreous haemorrhage, retinal detachment or rubeosis iriditis or glaucoma was present [12].
According to standard practice, dense cataract and blind patients with diabetes were also considered to have diabetic ophthalmopathy whenever it was impossible to establish the cause of their blindness. The severity of retinopathy was determined by the grading of the most seriously affected eye.
Statistical analysis
The data was coded and processed on IBM compatible computers, using the Statistical Package for Social Sciences (SPSS) software (version 13). Descriptive analysis, using standard statistical methods was performed. Chi-square tests and Fisher exact tests were used to ascertain the association between retinopathy and clinical variables. The Mantel-Haenszel test was used to adjust relationships between categorical variables for dichotomous confounders, while logistic regression was used to estimate the simultaneous effect of several determinants on a dichotomous (yes/no) outcome.