Comparison of culture-negative and culture-positive microbial keratitis: cause of culture negativity, clinical features and final outcome

Purpose To determine the causes of culture negativity and compare clinical outcomes in patients with culture-negative (CN) keratitis versus culture-positive (CP) keratitis. Methods Medical and microbiology records of 60 patients, who presented at the L V Prasad Eye Institute, Bhubaneswar, between January 2009 and December 2010, and who were clinically diagnosed to have microbial keratitis were retrospectively reviewed. Detailed ocular examination was performed before corneal scraping was sent for microbiological workup. The data collected from each record included age, gender, predisposing factors (ocular and systemic), clinical presentation, management and outcome of treatment. Results The duration of symptoms and prior use of topical medication was significantly higher in the CN group (p=0.005, p=0.007, respectively). Infiltrate size (p=0.42) and history of ocular trauma (p=0.14) had no association. While patients in the CP group underwent 9 (30%) minor major surgical procedures and 14 (46.7%) major surgical procedures, patients in the CN group underwent 11 (36.7%) minor surgical procedures and 1 (3.3%) major surgical procedure. Success in treatment was achieved in 27 (90%) and 25 (83.3%) patients in CP and CN groups, respectively. The mean visual acuity (logMAR) at presentation in the CP group was 2.53 which improved to 1.83 at the last follow-up (p=0.0001). Similarly, the mean visual acuity (logMAR) at presentation in the CN group was 2.57 which marginally improved to 2.34 at the last follow-up (p=0.03). Conclusions CN keratitis is associated with long duration of topical medication. The number of major surgical interventions in CN keratitis is significantly less compared with CP keratitis. However, the final outcome of treatment is similar in both CP and CN keratitis.