Diabetic retinopathy (DR) and nephropathy are the main microvascular complications of diabetes, with associations reported in many cross-sectional studies.1 In moving beyond cross-sectional associations, the article by Hseih et al2 in this issue of JAMA Ophthalmology uses prospective data to evaluate the association between renal profiles and DR in persons with type 2 diabetes. While this study shows clear evidence that information about kidney dysfunction can be informative about retinopathy, it implies that kidney dysfunction precedes retinopathy. This implied temporal causal path may not make sense for retinopathy and nephropathy, which likely share some common pathways.3,4 The confounding from this common pathway could be influencing these results. When the temporal order is not clear, there are a few considerations to keep in mind during analyses.
Lee KE. Considerations When Temporal Order Is Not Clear. JAMA Ophthalmol. 2018;136(1):74–75. doi:10.1001/jamaophthalmol.2017.5212
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