de Fine Olivarius et al. BMC Public Health 2011, 11:80 http://www.biomedcentral.com/1471-2458/11/80 effect of HbA1c, blood pressures, proteinuria and smok- ing as well as age and sex [19]. Among many candidate predictors we found only relatively high age, living alone and high triglycerides to be associated with worsening of visual acuity over 6 years, while high age, living alone, low self-rated health, and low level of physical activity were associated with a low level of visual acuity. Pre- sumably the three last-mentioned relations are cases of reverse causation where poor vision affects living condi- tions. Marital status has similarly been found to predict vision loss in men with older-onset diabetes [20], but the association was reversed in a study of patients with advanced DR [21]. In UKPDS the incidence of visual impairment was slightly lower in the tight vs. the less tight blood pres- sure control group [22]. Similarly, blood pressure, HbA1c and proteinuria have been shown to be indica- tive of visual loss in follow up studies [16,19,23], but none of these non-ocular patient variables was asso- ciated with visual loss in the present study. This could be due to measurement error and above all regression dilution bias [37], which is particularly relevant for bio- chemical and clinical variables in the dysmetabolic state of newly diagnosed clinical diabetes. In studies including patients with known diabetes [16,19,23], the measured risk factor levels are supposedly closer to an average steady state level, a kind of set point which is typical for the patient in question. In the present study, however, high level of triglycerides, which has been identified as a risk factor for proliferative DR [38], was a significant predictor of declining vision. In line with this finding, the FIELD study showed a promising reduction in the need for laser treatment for DR after treatment with fenofibrate but this did not affect worsening of visual acuity [39]. It is possible that DR mediates the effect of triglycerides on visual acuity in a slow, progressive pathophysiological process. The strong counter-intuitive inverse univariate relation between smoking and visual acuity disappeared after age and sex adjustment (Table 1) while a similar association between smoking and DR persisted after adjustment in UKPDS [40]. Prevalence and incidence of blindness and moderate visual impairment In population-based studies of patients with known type 2 diabetes the prevalence of blindness is between 1% and 3% [6,7,34,41-43], lowest in populations offered reg- ular eye screening. The prevalence increases markedly with diabetes duration [14,23,42,43], in the present study from 0.9% at diagnosis to 2.4% six years later (Table 3). With the gradual implementation of systematic eye screening the incidence of blindness among diabetic patients has declined [44]. In the Nordic countries the incidence per 10,000 person-years has declined from the Page 11 of 13 range of 200-500 [15,45] in the early 1980s to more recent figures of about 15 [23,46] among persons with known type 2 diabetes. Our patient sample included many old patients and both the prevalence [2,4,41] and the incidence [14,16,19] of visual impairment increases curvelinearly with age as in the background population [2,36,47]. This may partially explain why the incidence rate was as high as 40 per 10,000 person-years in the present study. In studies of patients with known type 2 diabetes, which are to some extent population-based, the preva- lence of 7-11% for moderate visual impairment [22,34,42,43] is similar to the 6.7% observed 6 years after diagnosis in the present study. Of the 54 patients with moderate visual impairment at this point, however, 48 had normal vision at diagnosis, but the prevalence rate increased only modestly because of the over-mortal- ity of patients with low vision [48]. Implications for clinical practice and future research It is evident that even in Denmark where patients can refer themselves to free eye examinations, treatable eye pathologies such as DR and cataract predict further visual loss. Our results underline the importance of eliminating barriers to efficient eye care by facilitating access to eye examination, increasing the understanding of patients and primary care practitioners of the need for regular screening and early surgical treatment, and, in some countries, addressing patients’ financial burdens [49]. It should be easy to motivate a thoroughly informed patient to have regular eye examinations as many patients fear visual loss as the worst consequence of diabetes [10,13]. The fact that almost all Danish pri- mary care eye doctors participated in the present study demonstrates the commitment of ophthalmologists to preventive diabetes care. In primary care, future intervention studies to reduce visual impairment in patients with diabetes may be designed primarily to overcome barriers to effective eye care, and such trials should preferably distinguish between the effect on visual acuity of changes in biologi- cal age on retina and of the interventions targeting trea- table eye pathologies. Conclusions To conclude, severely reduced sight is a very real chal- lenge for patients with newly diagnosed clinical, often symptomatic type 2 diabetes. During the first 6 years after diabetes diagnosis visual acuity deteriorates consid- erably, and this visual loss depends primarily on age and the presence of AMD, DR and cataract at diagnosis. Patients newly diagnosed with clinical type 2 diabetes should be made aware that there is an inevitable age- related decline in sight but that further vision loss