PurposeTo determine whether topical corticosteroids as adjunctive therapy for bacterial keratitis improves long-term clinical outcomes. DesignRandomized, placebo-controlled, double-masked clinical trial. MethodsThis multicenter trial compared 1.0% prednisolone sodium phosphate to placebo in the treatment of bacterial keratitis among 500 patients with culture-positive ulcers receiving 48 hours of moxifloxacin before randomization. The primary endpoint was 3 months from enrollment, and 399 patients were evaluated at 12 months. The outcomes examined were best spectacle-corrected visual acuity (BSCVA) and scar size at 12 months. Based on previous results, regression models with adjustments for baseline status and/or causative organism were used for analysis. ResultsNo significant differences in clinical outcomes by treatment group were seen with the prespecified regression models (BSCVA: −0.04 logMAR, 95% CI, −0.12 to 0.05, P = .39; scar size: 0.03 mm, 95% CI, −0.12 to 0.18, P = .69). A regression model including a Nocardia-treatment arm interaction found corticosteroid use associated with a mean 1-line improvement in BSCVA at 12 months among patients with non-Nocardia ulcers (−0.10 logMAR, 95% CI, −0.19 to −0.02, P = .02). No significant difference was observed in 12-month BSCVA for Nocardia ulcers (0.18 logMAR, 95% CI, −0.04 to 0.41, P = .16). Corticosteroids were associated with larger mean scar size at 12 months among Nocardia ulcers (0.47 mm, 95% CI, 0.06-0.88, P = .02) and no significant difference was identified by treatment for scar size for non-Nocardia ulcers (−0.06 mm, 95% CI, −0.21 to 0.10, P = .46). ConclusionsAdjunctive topical corticosteroid therapy may be associated with improved long-term clinical outcomes in bacterial corneal ulcers not caused by Nocardia species.