INS and eye disorder: The slightly higher prevalence of obesity (2.71% vs. 2.15%), eye disease (18.55% vs. 17.15%) and insulin use (8.32% vs. 6.22%) in never users and the slightly higher prevalence of sulfonylurea use (75.43% vs. 72.69%) in ever users in the matched cohort were unlikely to cause significant residual confounding because all of their standardized differences were <10%.