Purpose: To determine the feasibility of a case-control study of phosphodiesterase (PDE)-5 inhibitors and nonarteritic ischemic optic neuropathy (NION). Design: Retrospective cohort study using the National Veterans Health Administration's pharmacy and clinical databases. Methods: setting: National database. patient population: Male veterans 50 years of age and older with newly diagnosed NION or "possible" NION. interventional procedure: Dispensed prescription for a PDE-5 inhibitor. outcome measure: Incidence of NION and "possible" NION based on exposure to PDE-5 inhibitors. Results: The relative risk of NION among men prescribed a PDE-5 inhibitor was 1.02 (95% confidence interval [CI]: 0.92 to 1.12). The relative risk of possible NION among men prescribed a PDE-5 inhibitor was 1.34 (95% CI: 1.17 to 1.55). Conclusions: The collective risk of NION and possible NION was marginally significant (relative risk [RR] 1.10 95% CI: 1.02 to 1.20). A case-control study, in which the dependent variable is NION and the effect size of the PDE-5 inhibitor is assumed small, is feasible.
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