Despite medical advancements in available therapies, bacterial corneal infection frequently results in vision loss. Contact lens wear is a common predisposing factor for corneal infection; other reported risk factors are dry eye syndrome, blepharitis, trauma, and surgery. Both the immune defense against infection and the pathogenic mechanisms bacteria employ have been studied in vitro. However, there are complex interactions between the pathogen, the immune system, and the corneal tissue in vivo. Animal models allow the researcher to take the results of in vitro assays and validate their role in corneal infection in a living organism. A murine model is frequently used for studies of the pathogenesis of corneal infection caused by Pseudomonas aeruginosa. In this study, a modified scoring system is introduced that was designed to increase the information derived from this infection model. The new system includes evaluation of area, density, and surface characteristics of the ulceration. Results of in vitro experiments had previously indicated that ExsA, a transcriptional regulator of virulence-associated proteins, was important in pathogenesis of corneal infection caused by P. aeruginosa. Here we use the new scoring system to demonstrate in vivo that ExsA is involved.