Author's Response to comments on “Depth, size of infiltrate, and the microbe – The trio that prognosticates the outcome of infective keratitis”

Dear Editor, We thank the author, Thomas,[1] for their interest in our paper “Depth, size of infiltrate, and the microbe – The trio that prognosticates the outcome of infective keratitis”. As appropriately mentioned by Thomas,[1] earlier published reports do mention a large ulcer size and a deeper infiltrate, and some species such as Aspergillus have poorer outcomes, which we too have acknowledged in our manuscript. However, what remains unclear is whether infiltrates of similar size and depth caused by bacterial or fungal or any other microorganism would exhibit similar behavior. The series by Chidambaram et al.[2] similarly did not compare the outcomes of individual organisms based on the dimensions of infiltration. Although they did identify deeper involvement and larger infiltrates, along with Aspergillus, as risk factors for poor outcomes, they did not specifically investigate whether infiltrates of similar dimensions caused by Streptococci. P. would fare better than those caused by Aspergillus.[1] Our primary objective was to elucidate whether the increased size or deeper involvement of the infiltrate had a greater influence on the outcome among various organisms and thus to analyze if an interplay exists between the trio that would help prognosticate the outcome of microbial keratitis. To achieve this, we grouped our patients into categories based on ulcer size and infiltrate depth as group A: ulcer size < 6 mm with anterior to mid stromal infiltrate, group B: ulcer size < 6 mm/full-thickness infiltrate, group C: ulcer >6 mm/anterior to mid stromal infiltrate, and group D: ulcer >6 mm/full-thickness infiltrate and then compared the outcomes of individual organisms. Virulence is the term used to describe the ability of a microbe to cause a disease. However, there is still no consensus on its precise definition.[3] The pathogenicity of microorganisms is determined by the nature and type of different virulence factors they possess.[4] Although we did not individually assess virulence factors, the differential outcomes observed based on similar infiltrate dimensions and adherence to recommended treatment regimens for different organisms led us to conclude that “an interplay among the size of the infiltrate, the depth of involvement, and the virulence of the organism determines the outcome of IK.” As acknowledged by Thomas,[1] this conclusion was supported by the better response of Acanthamoeba keratitis to medical management compared to Pythium keratitis, irrespective of size and depth. Furthermore, we observed that, except in bacterial infections, the size of the infiltrate was directly proportional to a poorer outcome, whereas it was the depth of involvement in bacterial keratitis. This observation may be explained by the literature evidence suggesting higher expression of pro-inflammatory genes and autolytic enzymes, along with the downregulation of collagen subunits, in bacterial keratitis. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.