Shorter axial length or hyperopia has been reported to be associated with a lower socioeconomic background, so that by not including the socioeconomic background into the multivariate model, a bias might be introduced. The reason for these associations may be the anatomy of the retinal venous blood system which drains through the central retinal vein through the optic nerve and the orbital cerebrospinal fluid space via the superior ophthalmic vein into the intracranial venous system. One may infer that the blood pressure in the central retinal vein inside of the eye is at least as high as the CSFP. An experimental study in monkeys accordingly showed that the central retinal vein pressure and CSFP were directly correlated with each other, in the normal state and in the situation of an elevated CSFP. An elevated retinal vein pressure in patients with higher CSFP will be associated with a higher retinal capillary blood pressure potentially explaining the increased incidence and prevalence of retinal hemorrhages, edema and lipid exudates as part of DR. As recently suggested by Stodtmeister and colleagues, an elevated retinal venous pressure due to an increased CSFP may additionally decrease the ocular perfusion pressure defined as the difference between the retinal arterial blood pressure and the retinal venous blood pressure. A decrease in the ocular perfusion pressure leads to an increase in the risk for ischemic retinopathies such as DR. If the association between higher CSFP and incidence of DR is further clarified in future studies, one may address the question whether lowering of CSFP by drugs such as systemic carbonic anhydrase inhibitors may have a therapeutically positive effect on the development of DR. The association between higher estimated CSFP and DR may also explain the dilatation of retinal veins and their increased tortuosity as hallmarks of DR. An increased arterial blood pressure alone may not explain why on the venous side of the vascular bed the vessels get wider. In our study, lower level of education was another marginally significant risk factor for an increased incidence of DR in the multivariate analysis. Correspondingly, rural region of habitation with a lower mean educational level as compared to urban regions was associated with a higher incidence of DR in the univariate analysis. It may show the importance of the socioeconomic background in terms of lifestyle, understanding of the importance of a therapy of diabetes and the financial possibilities to do so. Designers of future studies on DR and on diabetes mellitus in general may consider including the educational level or other parameters of the socioeconomic background into the study designs. Potential limitations of our study should be mentioned. First, as in any population-based study, selection bias could have accentuated some estimates and masked others. The overall participation rate in our survey was 60.7% of the Trichostatin A original cohort, or 66.4% of the survivors, so it is possible that nonparticipation may have influenced the results of our study. Compared with other 10-year follow-up studies in ophthalmic epidemiology, the response rate in our study was lower than that in the Blue Mountains Eye Study and the Beaver Dam Eye Study. The reason for the lower follow-up response in the current study is the presumably higher mobility of the population in Greater Beijing compared with the mobility of the populations from the Blue Mountains Eye Study and Beaver Dam Eye Study. Because of intensive land development activities in the rural region and the urban regions of the Beijing Eye Study, a substantial number of inhabitants moved away during the follow-up period.