**2. Etiology**

Even during refractive surgery there may be contamination by bacteria in the corneal stroma in up to 24% of cases. These bacteria are mostly of Gram-positive type, in most cases, *Staphylococcus epidermidis*, which does not necessarily manifest as infectious keratitis due to stromal defense mechanisms [6]. The causative agents fall within the same spectrum across the different surgical techniques. Atypical mycobacterial keratitis related to inadequate sterilization has also been described, including superficial punctate keratitis, contact lens use, and other history of previous refractive surgery or touch-ups, particularly radial keratotomy [7, 8].

Currently, the most frequently related agents are Gram-positive cocci [8, 9]. Although less frequently, other possible causative agents have been reported, namely, additional Gram-positive bacteria such as *Nocardia spp* and *Corynebacterium spp*, Gram-negative bacteria such as *Pseudomonas aeruginosa* and *Serratia*, fungi, *Acanthamoeba*, and even polymicrobial infections. Also, among the most common causative agents of viral infections are adenovirus [10–13].

## **3. Risk factors**

The following have been identified as the main predisposing factors for infection: disruption of the barrier function of the corneal epithelium, use of bandage contact lenses and topical corticosteroids, history of blepharitis, previous corneal surgery, contamination during surgery, dry eye, lack of perioperative antibiotics, and herpes simplex virus (HSV) infection [14, 15]. The use of contaminated surgical instruments, the surgeon's hands, the presence of infectious agents on the ocular surface, and environmental conditions could also be associated with contamination and hence with the development of corneal infections [16].

Several factors inherent in the procedure explain the increased risk of infection after a photorefractive keratectomy (PRK) compared with other techniques. Among them, the defect in the epithelium caused during surgery, and the time of about 4 days for its regeneration, entails a loss of the protective function of the corneal epithelium and may create an area prone to adhesion and reproduction of microorganisms. Other factors are the use of therapeutic contact lenses, which are routinely used after surgery, and the use of topical corticosteroids [15, 17].

#### *Infectious Keratitis after Surgery DOI: http://dx.doi.org/10.5772/intechopen.113078*


#### **Table 1.**

*Risk factors associated with infectious keratitis.*

#### **Figure 1.**

*Slit-lamp microscopy image of the patient's right eye showing a central infectious infiltrate.*

In addition, a recent retrospective study has linked the use of face masks in the previous COVID-19 pandemic with a slight increase in the incidence of infectious keratitis in patients undergoing refractive surgery [18]. Another risk factor to be considered is the possible link with methyl-resistant infectious agents [18, 19] (**Table 1** and **Figure 1**).
