The Eye is the Window to the Kidney and Brain

Abstract

Diabetic retinopathy and age-related macular degeneration are leading causes of blindness among older adults. Both conditions are more prevalent among those with chronic kidney disease (CKD). However, few if any previous examinations of CKD and visual impairment (VI) have been conducted. This gap in knowledge is filled by Wong et al. (2016) in their article published in this issue of EBioMedicine. The prevalence of VI and associations between CKD, VI and other major ocular diseases are reported for Asian adults between 40 and 80 years of age participating in the Singapore Epidemiology of Eye Disease (SEED) Study between 2004 and 2011 (n = 9434). Chronic kidney disease (estimated glomerular filtration rate < 60 mL/min/1.73 m2) was defined using the Kidney Disease Outcomes Quality Initiative (KDOQI) Work Group definition and diagnosis of VI and other major ocular diseases were based on comprehensive ophthalmological examination. The prevalence of VI and any ocular disease were significantly higher in those with CKD (36.1% and 84.7%) than in those without (12.9% and 54.3%). Moreover, CKD was associated with significantly higher risk of VI, any ocular disease, cataracts, any retinopathy and diabetic retinopathy after adjustment for potential confounders (odds ratios ranging from 1.24 to 1.94). This paper makes a valuable addition to the literature because adequate vision is fundamental to quality of life and many forms of blindness are treatable and preventable (Wong et al., 2016). One impressive aspect of the study, apart from the very large sample, is that multiple eye disease outcomes are presented in a single study (i.e., those previously mentioned as well as glaucoma). The benefits of comparing different outcomes within the same study, as compared to different studies using different samples and methods, are obvious. The selection and modeling of covariates to adjust for confounders reflects the authors' understanding that “the high occult burden of ocular disease may be explained in part by risk factors common to both eye and kidney disease” (Wong et al., 2016). The models represent an exhaustive list of theoretically and clinically relevant cardiovascular disease covariates. We were, however, disappointed in the lack of any variable indexing inflammation (e.g., C-reactive protein, but see Table 1 for an extended list), an important mechanism underlying CKD and ocular disease, particularly among those with diabetes mellitus. This is discussed by Wong et al. (2016), although they did not list it as a limitation of their study. Additionally, late stages of CKD were examined in relation to VI and ocular diseases without considering physiological complications of treatment that have been previously identified (Murray, 2008, Chelala et al., 2015). Table 1 Inflammatory markers identified in the cardiovascular literature.