At diabetes diagnosis median (IQR) age was 65.5 (56.0-73.6) years, male/female ratio was 1.11 (653/588), and median diagnostic plasma glucose was 13.7 (10.7-17.0) mmol/l. The prevalence (95% confidence interval) of blindness and moderate visual impairment was 0.9 (0.4-1.4) % and 5.4 (4.1-6.7) %, respectively (Table ). AMD, other non-diabetic retinopathy and, above all, cataract were common. The ophthalmologists estimated that cataract was the most common cause of visual impairment except among the blind (Table ). At diagnosis the eye doctors reported glaucoma in the best seeing eye in 18 (1.5%) of 1241 patients. 13 had normal visual acuity and 5 had impaired vision.
Visual acuity at diabetes diagnosis according to age, sex, retinopathy, and cataract
Change in visual acuity
Among the 807 surviving and re-examined patients, visual acuity generally deteriorated (Table ). The prevalence (95% confidence interval) of blindness and moderate visual impairment was 2.4 (1.3-3.4) % and 6.7 (5.0-8.4) %, respectively, 5.6 (5.0-6.3) years (median, IQR) after the first eye examination. The 18 new-blind patients in Table represent an incidence (95% confidence interval) of blindness of 40.2 (25.3-63.8) per 10,000 patient-years. Of 18 new-blind patients, 14 were over 70 years. The incidence of moderately impaired vision or worse was 142.3 (110.5-183.2) per 10,000 patient-years among patients with normal sight at diagnosis. Of the 25 patients in Table with moderate visual impairment at baseline, 14 had normal visual acuity 6 years later. Of these 14 patients, 7 had had a cataract operation since the baseline examination and one had had a retinal laser treatment.
Changes in visual acuity from diabetes diagnosis until 6-year follow up
During the 6 years of follow up, DR had appeared in 11.7% (90/770) of patients without DR at diagnosis (Table ). At 6-year follow up, DR and AMD were also relatively more common among the visually impaired (Table ). The influence of eye complications at diagnosis on change in visual acuity over 6 years was investigated in linear mixed models (Table ). The 112 patients in Table with "other retinopathy" presented with133 retinal pathologies other than DR and AMD: hypertensive retinopathy (n = 43), retinal vasosclerosis (41), drusen (18) and other retinopathy (31). DR (n = 52), AMD (154), and cataract (337) were associated with the level of visual acuity and/or its annual change also in age- and sex-adjusted analyses. These effects are illustrated with median decimal acuity values in Figure .
Prevalence of diabetic retinopathy at diabetes diagnosis and at 6-year follow up
Visual acuity and retinopathy 6 years after diabetes diagnosis
Figure 2 Vision loss during the first 6 years after diabetes diagnosis according to all statistically significant predictors at diagnosis except fasting triglycerides and self-rated health. The curves are defined by medians of decimal acuity (interquartile ranges) (more ...)
Similarly, some socio-demographic, clinical, biochemical, and behavioural variables affected the level of visual acuity and/or its annual change over 6 years even when the effect of age and sex was considered (Table ). All significant effects, except that of self-rated health and triglycerides, are illustrated in Figure . The effect of triglycerides was not picked up by the median values. This is because the median figures in Figure emphasize typical developments in visual acuity, while the result of the statistical analysis is necessarily based on logMAR values and expressed as means which are greatly affected by patients with very poor eye sight (Table ).
When the changes in visual acuity were modelled as piecewise linear models with a breakpoint 3 years after diagnosis, the annual change in logMAR before (0.0268, p < 0.0001) and after this point (0.0231, p = 0.0008) was similar (p = 0.99 for the significance test of the time-logMAR interaction). Accordingly, visual loss during the first years after diabetes diagnosis did not seem to be greater than later on, which supports the underlying assumption in Figure that visual loss follows a linear course.
Adding the identification number of the eye doctors as a random effect to the models in Table did not change the associations with developments in visual acuity. Therefore, it is unlikely that our results are affected by the fact that some patients were examined by the same eye doctor at baseline and follow up, while others were not.