Excimer laser ablative treatment of microbial keratitis.

The 193-nm excimer laser was used to ablate experimental septate fungal (Fusarium) and an atypical mycobacterial (Mycobacterium fortuitum) keratitis in an animal model. The infections were allowed to proceed for 24 and 72 hours. After incubation, ablation with a 193-nm excimer laser with 5.0-mm treatment zones was performed until all suppurative areas were treated. The corneas were excised, halved, homogenized, and plated. All cultures were negative in the 24-hour group. However, in those corneas in which the infections were allowed to proceed to 72 hours, post-treatment cultures were positive for both organisms. Histopathologic examination confirmed that 24-hour infections had been eradicated and that 72-hour infections had organisms present. Three of the eight eyes in the M. fortuitum group perforated during treatment, even though the treatment depth by computer preselection was only 150 microns. Excimer laser photoablation may be a useful technique to eradicate early, localized microbial infections. However, it is apparent that advanced infections with deep stromal involvement and suppuration cannot be eradicated using this technique. Because corneas may be perforated inadvertently during treatment, excimer laser treatment of infectious keratitis should be approached with caution and used for superficial and well circumscribed lesions.