Hyperguides

Ophthalmology / Refractive surgery

Post-LASIK Atypical Mycobacterial Keratitis

Neda Shamie, MD Peter J. McDonnell, MD
Article


Introduction

Mycobacterium chelonai is a rapidly growing nontuberculous mycobacterium omnipresent in soil, food, and tap and laboratory water.1-4 It is a member of the M. fortuitum complex that is also composed of M. fortuitum and M. abscessus.5-8 These organisms are believed to be common contaminants as they can multiply rapidly in distilled water and can remain viable for up to a year despite exposure to chemical disinfectants such as chlorine.1,3,9 Reported mycobacterial ocular infections include postoperative or posttraumatic keratitis and endophthalmitis, orbital granuloma, dacryocystitis, and scleral abscesses.10 M. chelonai is a commonly reported and difficult-to-treat cause of keratitis related to refractive corneal surgery including radial keratotomy, photorefractive keratectomy and laser in situ keratomileusis (LASIK).1,2,9,11-13

Clinical Presentation

The clinical presentation of nontuberculous mycobacterial keratitis after LASIK is often confused with signs of diffuse lamellar keratitis (DLK). Whereas topical corticosteroids improve the course of DLK, postoperative corticosteroids are believed to contribute to the proliferation of these organisms and worsening of the signs and symptoms.6,8,9 The routine use of postoperative corticosteroids likely limits the host response to this organism, so that the lesions often have remarkably discrete borders and lack the appearance of a typical infectious infiltrate. The clinical course is often protracted, as the causative organism may be difficult to identify and the standard ophthalmic antibiotics are not considered particularly effective against this class of organisms. The diagnosis may finally be entertained when patients develop the distinctive focal infiltrates at the level of the interface described as a "cracked windshield" appearance and permanent stromal scarring.2

Treatment

The current treatment regimen for this dreaded complication of refractive surgery is not consistent and can include any combination of fortified topical amikacin, ciprofloxacin, or clarithromycin.1,14-16 Despite aggressive antibiotic treatment and due to resistance to currently available antibiotics, the infection often progresses to flap necrosis requiring flap amputation and to stromal scarring requiring corneal transplantation.2,6,9,11,17-23 Approximately 80% of reported cases require flap amputation to allow the infection to finally resolve. With these limitations and with the increased incidence of postoperative atypical mycobacterial keratitis, there is a need for a more efficacious prophylactic as well as therapeutic agent.

Since their advent, fluoroquinolones have been recognized as a superior class of antibiotics with each higher generation having greater coverage against both gram-negative and gram-positive bacteria.24 Fourth-generation fluoroquinolones, being the most recently developed class of fluoroquinolones, consist of gatifloxacin and moxifloxacin. These antibiotics were introduced to counteract the reported high prevalence of bacterial resistance to the second- and third-generation fluoroquinolones.24 Gatifloxacin was approved by the Food and Drug Administration for the treatment of gonorrhea and respiratory and urinary tract infections.25 Since then, gatifloxacin has gained popularity among clinicians in the treatment of atypical and complicated systemic infections due to commonly encountered gram-positive and gram-negative bacteria.26-29 Recently, many groups have tested its in vitro efficacy against M. tuberculosis, M. avium and other atypical nontuberculous mycobacteria such as M. marinum.30-34 Given the in vitro evidence demonstrating gatifloxacin's activity against atypical mycobacterium species, it can be speculated that new generation fluoroquinolones such as gatifloxacin may prove to be useful in the treatment for atypical mycobacterial keratitis. In a rabbit model of post-LASIK keratitis, we have shown that the infectious keratitis caused by inoculation of a strain of M. chelonai under a lamellar flap was eradicated after a four-times daily treatment of topical gatifloxacin for only 3 weeks (submitted for publication). The clinical implications from these results are germane to the practice of the clinical ophthalmologist and refractive surgeon. Clinical studies are required to verify the applicability of these results to humans.

Conclusion

The difficulty of treating infections caused by atypical mycobacteria underscores the need for prevention. Although chemical disinfectants may be adequate for reducing or eliminating most bacterial contaminants, this class of organisms is not successfully eradicated with such solutions. Heat sterilization is therefore recommended as the technique of choice for sterilizing equipment that is not damaged by heat and that may come in contact with the eye during keratorefractive surgery. Surgeons should be judicious when using equipment on the cornea that cannot be heat sterilized, such as the tips of ultrasonic pachymeters, and balance their value against the fortunately very small risk of infection.

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