de Fine Olivarius et al. BMC Public Health 2011, 11:80 http://www.biomedcentral.com/1471-2458/11/80 present for many years before vision begins to decline as a result of these pathologies. In the history of diabetes treatment, the development of diabetic retinopathy has been included in the out- come of numerous clinical trials though prevention of visual loss is the ultimate target for the patients. While the ocular predictors of future visual loss in diabetic patients are well-described [14-19], a comprehensive prospective study of ocular and non-ocular predictors of long-term changes in measured visual acuity has not been published before [14,16,19-23]. Our main aim was to study a broad range of predic- tors of vision loss in a population-based sample of patients newly diagnosed with type 2 diabetes and observed for 6 years. Methods Study population In the Danish Diabetes Care in General Practice study [24], 474 general practitioners agreed to include all sub- jects with newly diagnosed diabetes on their practice list (Figure 1). The 140 patients without a measurement of visual acuity at diagnosis did not differ from the 1,241 patients who were included in the present study regard- ing age (p = 0.36), sex (p = 0.31) and diagnostic plasma glucose (p = 0.81). At 6-year follow up, the 159 non- censored patients without information about visual acuity (Figure 1) did not differ from the 807 re-exam- ined patients with regard to age (p = 0.23), sex (p = 0.82), diagnostic plasma glucose (p = 0.43), prevalence of DR at diagnosis (3.2% (5/158) vs. 4.4% (35/800), p = 0.49) and prevalence of moderately impaired vision or worse at diagnosis (7.0% (11/159) vs. 3.3% (27/807), p = 0.10). A small number started insulin treatment within 180 days of diagnosis, so 97.6% of the 1381 patients who had started in the study were considered to have type 2 diabetes [24]. Informed consent was obtained from all participants, and the protocol was approved by the ethics committee for Copenhagen and Frederiksberg. Ophthalmologic examination Immediately after diabetes diagnosis, the general practi- tioner referred the patient to a practising ophthalmolo- gist who did a standard eye examination. The result of the funduscopy was recorded by the ophthalmologist in a multiple choice question with six response categories: no diabetic lesions, microaneurysms only, background retinopathy without or with maculopathy, and prolifera- tive retinopathy without or with new vessels on the optic disc. In open-ended questions information about other retinal pathologies, glaucoma, and eye operations was given, and the presence of cataract was indicated in a closed question. Information about glaucoma was also given as answers to open-ended questions about reasons Page 2 of 13 Inclusion criteria: 474 doctors were to include all patients on their practice list fulfilling the following criteria: 1) Diabetes mellitus diagnosed from 1 March 1989 to 28 February 1991 (71 doctors volunteered for a 1-year extension of this period) 2) Based on hyperglycaemic symptoms and/or raised blood glucose values measured in general practice, the diagnosis was established by a single whole blood or plasma glucose concentration 7.0/8.0 mmol/l measured at a major laboratory 3) Age 40 years or older at diagnosis Eligible patients (n = 1590) Primary exclusions: Severe somatic disease (n = 50) Severe mental illness (n = 50) Declined to consent (n = 62) Secondary exclusions: Diagnosis not confirmed (n = 47) Patients included in main study (n = 1381) Patients with visual acuity measured at diabetes diagnosis and included in the present study (n = 1241) Missing eye examination at diabetes diagnosis (n = 137) Missing measurement of visual acuity (n = 3) Died before follow-up (n = 264) Withdrew consent (n = 7) Lost to follow-up (n = 4) Missing eye examination at follow-up (n = 154) Missing measurement of visual acuity (n = 5) Patients with visual acuity measured at diagnosis and 6-year follow-up (n= 807 ) Figure 1 Flow of participants through study. for impaired vision. Visual acuity with best correction was estimated with an optotype chart, usually a Snellen chart, and given for each eye as the Snellen ratio at 6 metres or 20 feet or as decimal acuity, but all mea- surements were converted to decimal acuity and log- MAR [25]. The time (interquartile range, IQR) from diabetes diagnosis until the first eye examination was 45 (24-83) days. A total of 164 ophthalmologists partici- pated, and 68.5% (553/807) of patients were seen by the same ophthalmologist at first and last eye examination. The eye with best visual acuity was used for evaluation of retinal pathology. Assessments The doctors recorded the following information about the patient: height and weight without shoes and outer garments; blood pressure and heart rate by routine methods after a 10-minute rest in a sitting position; sense of touch of cotton wool and pin prick on both feet; presence of dorsalis pedis or posterior tibial pulse on both feet; presence of patellar reflexes; history of