In recent years, there has been an explosion of research articles using large population databases in clinical research; ophthalmology is no exception. In 2012, using the British Columbia Ministry of Health database, we published one of the first population-based pharmacoepidemiologic studies1 that found an elevated risk of retinal detachment (RD) (relative risk, 4.50; 95% CI, 3.56-5.70) with oral fluoroquinolones (FQs). Since 2012, several large epidemiological studies on this topic have been published with conflicting results.2-4 For example, Kuo et al2 used the national health database of Taiwan and undertook a retrospective cohort study. Measured covariates and potential confounders were appropriately adjusted for using propensity score analysis. The overall relative risk for RD was found to be 2.07 (95% CI, 1.45-2.96). However, exposure to FQ was defined as greater than 3 consecutive prescriptions. It wasn’t clear from the study why this definition of exposure was used. This means that, by design, participants could not have experienced an RD before the first 3 prescriptions, leading to a survival bias referred to as immortal time bias, which usually underestimates the true risk.