Comparison of Recurrent and Naïve Keratitis in a Cohort of 1303 Patients.

: Microbial keratitis is a precursor to corneal scarring, the fifth-leading cause of blindness and visual impairment worldwide. Despite its significance, there is a paucity of data quantifying the recurrence rates of keratitis and the subsequent corneal damage. This study aims to address this gap by providing a comprehensive analysis of the frequency and origin of keratitis recurrences and its impact on visual deterioration. : We retrospectively analyzed a cohort of 1303 patients diagnosed with microbial keratitis at the Independent Public University Eye Hospital in Warsaw, Poland, between January 2018 and December 2023. All adult patients with at least one documented episode of infectious keratitis were included in the study. Patients were divided into two cohorts: Group 1: patients with recurrent keratitis (n = 233) and Group 2: patients with the first episode of keratitis (n = 1070). : The recurrence rate of keratitis was 17.88% (233 of 1303 patients), regardless of etiology. Visual acuity on admission did not differ significantly between the recurrent and naïve groups. However, among patients with at least three episodes, visual acuity was worse (median logMAR for 1 vs. 2 vs. 3 recurrences were the following: 0.30 (0.08-0.67) vs. 0.60 (0.12-1.30) vs. 0.44 (0.20-0.92), accordingly, = 0.049). Univariate logistic regression identified contact lens usage as a significant risk factor for recurrence (OR 2.37, 95% CI: 1.84-3.08, < 0.001), also including its inappropriate use (OR 2.25, 95% CI: 1.42-3.66, = 0.001). In terms of etiology, bacteria were the most common identified cause of keratitis in both the recurrent and naïve groups, accounting for 38.36% (90 cases) in Group 1 and 47% (503 cases) in Group 2. Viruses were the second most prevalent etiology, representing 31.33% (73 cases) in Group 1 and 19.91% (213 cases) in Group 2. Furthermore, a multivariate logistic regression model indicated that advanced age, delayed treatment, fungal etiology, and post-corneal transplant status were strongly associated with worse visual outcomes. : Although each recurrence contributes to cumulative vision loss, the majority of patients with recurrent keratitis present with a useful visual acuity (0.3 to 0.60 logMAR). Our study identified older age, fungal etiology, delayed treatment, and post-keratoplasty keratitis as the most significant risk factors for visual deterioration. These findings underscore the need for targeted interventions in populations at higher risk of adverse visual outcomes.