Microbial keratitis is an infection of the cornea that is associated with risk of permanent visual impairment.

It can be caused by bacteria, virus, fungus, protozoa and parasites. The common risk factors for infectious keratitis include ocular trauma, contact lens wear, recent ocular surgery, preexisting ocular surface disease, dry eyes, lid deformity, corneal sensation impairment, chronic use of topical steroids and systemic immunosuppression .

The spectrum of bacterial keratitis can also be influenced by geographic and climatic factors.

The treatment usually consist of Topical administered antibiotics .the emergence of multidrug-resistant bacteria is a concern that might complicate the treatment and cure of infectious keratitis.

Collagen cross linking (CXL) using ultraviolet-A (UV-A) and riboflavin in a treatment that was developed to increase the biochemical strength of the cornea The procedure is based on using riboflavin as a photosensitizer, which generates reactive oxygen species when activated by UV-A at 365 or370 nm.

The standard technique (epi-off) also called Dresden Protocol includes removal of the epithelium in order to expose the underlying stroma to riboflavin, which is otherwise incompletely absorbed by the epithelium because of tight junctions. The area of corneal epithelium removed has a diameter of 6.0 to 8.5 mm. A crosslinking procedure without epithelial removal could also be performed (epi-on). It would likely be less painful compared to the standard procedure.

The crosslinking process generates reactive oxygen species that can damage the cell walls of pathogens. CXL induces formation of new covalent bonds thereby rendering the corneal stroma biomechanically stronger and more resistant to enzymatic digestion . This can potentially limit the spread of infection. Furthermore, CXL-induced apoptosis could contribute to the reduction of inflammatory response during corneal infection .

Inclusion Criteria:

• Patients with proved bacterial, fungal, acanthamoeba microbial keratitis .
• Patient willing to comply with all study procedures .

Exclusion Criteria:

• Severe corneal scarring or opacification .
• Patients with viral infectious keratitis
• Prior herpetic infections .
• Patients with any coexisting ocular pathology,ocular surface disease .
• Patients with Autoimmune disease.
• Pregnant women .
• Corneal Thickness of less than 400 microns .