Efficacy of topical gentamicin treatment after 193-nm photorefractive keratectomy in an experimental Pseudomonas keratitis model

Abstract

Background: The treatment of Pseudomonas keratitis has many limitations, and further investigation to identify more effective approaches is required. We therefore studied the possible contribution of the debridement effect of 193-nm excimer laser on Pseudomonas keratitis in rabbit eyes.

Methods: Pseudomonas keratitis was induced in 30 rabbit eyes by inflicting controlled central corneal scratches and applying a drop of Pseudomonas aeruginosa suspension. After 24 h, one cornea of each animal was photo-ablated (excimer laser: fluency 90 mJ/cm2, 10 Hz, 213 pulses), yielding 50 microns of tissue ablation, while the follow cornea served as control. Five groups of six animals each were formed and received: a subconjunctival injection of gentamicin 20 mg (group 1), topical 14 mg/ml gentamicin hourly (group 2) or every 2.5 h (group 3), or NaCl 0.9% hourly (group 4) for 8 h. In group 5, animals were sacrificed without additional treatment. After 9 h corneas were excised, homogenized, serially diluted, and plated on agar blood plates. The numbers of colony-forming units (CFU) per cornea were statistically evaluated (Mann-Whitney test).

Results: In control eyes, a greater decrease of CFU was observed in group 2 than in group 3 (P = 0.03). In laser-ablated eyes, there was no difference in CFU between groups 2 and 3. Comparison of the excimer-treated and control eyes revealed a greater number of bacteria (CFU) in controls only in group 3 (P = 0.02).

Conclusion: Our study suggests that controlled debridement of cornea with excimer laser may improve the effect of topical antibiotics.