**1. Introduction**

[57] Harr DL, Quencer RM, Abrams GW. Computed tomography and ultrasound in the evaluation of orbital infection and pseudotumor. Radiology 1982; 152: 395.

[58] Brook I, Frazier EH. Microbiology of subperiosteal orbital abscess and associated

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146 Common Eye Infections

*Mycobacterium* species that are considered typical are the tuberculosis species such as *M.tu‐ berculosis*, *M.bovis*, *M.africarium* and *M.leprae*. These species have only human or animal res‐ ervoirs and are not transmitted by water. In contrast, the species Non-Tuberculosis or "atypical", naturally are ubiquitous in soil and water and have been found as normal flora of skin, sputum, and gastric contents. These bacteria are resistant to common, disinfectants, chlorine, formaldehyde and glutaraldehyde.

NTM can cause infections on all adnexal and ocular tissues including the cornea, iris, lens, retina, choroid and optic nerve. Most NTM infections are caused by *M.chelonae* and *M. fortu‐ itum*, that as we will discuss later, belong to the rapid growers group.

In this chapter, we will focus on keratitis caused by atypical mycobacterium, since a great number of recent clinical reports of NTM ocular infections are of keratitis. In common gener‐ al ophthalmology procedures like refractive surgery, for example laser in situ keratomileusis (LASIK), Laser epithelial keratomileusis (LASEK), photorefractive keratectomy (PRK), and other specialized procedures such as penetrating keratoplasty (PKP), a transgression to nat‐ ural barriers occurs, this constitutes a risk factor for infection by these organisms. In addi‐ tion, LASIK is one of the most commonly performed procedures in ophthalmology practice.

Several factors may contribute to the development of mycobacterial keratitis following LA‐ SIK, making it difficult to determine the true origin of the infection in most cases. This pro‐ cedure is often performed utilizing aseptic, but non sterile techniques. *Mycobacterium*

*chelonei*, *M. abscessus*, *M. fortuitum*, *M. szulgai*, and *M. mucogenicum* have been reported as the result of improper asepsis.

Atypical Mycobacteria corneal infections are rare, but devastating complications. Although rare, are a diagnostic and therapeutic challenge. Mycobacterium have been involved in sev‐ eral isolated cases as well as in outbreaks.[4-12]
