Histopathologic Evaluation of Corneal Tissue After Adjunctive Rose Bengal Photodynamic Antimicrobial Therapy and Keratoplasty in Advanced Acanthamoeba Keratitis

<b>Background/Purpose</b>: To compare the microbiologic and histopathologic features of Acanthamoeba isolates recovered from patients with Acanthamoeba keratitis (AK) who underwent a therapeutic penetrating keratoplasty (TPK), optical penetrating keratoplasty (OPK), or deep anterior lamellar keratoplasty (DALK) after Rose Bengal Photodynamic Antimicrobial Therapy (RB-PDAT). <b>Methods</b>: Surgical specimens were stained with hematoxylin, eosin, and Periodic Acid-Schiff stains as per institutional protocol at the University of Miami, Bascom Palmer Eye Institute. Analysis of Acanthamoeba cyst depth, number of cysts, and average corneal thickness was established by light microscopy. <b>Results</b>: Seventeen patients with AK underwent surgical intervention and RB-PDAT. Eight patients underwent a TPK and nine patients underwent an OPK/DALK. In the TPK group, average cyst depth was 42.0 ± 52.5 μm from Descemet's layer and mean corneal button thickness was 661.7 ± 106.5 μm. Comparatively, in the OPK/DALK group, average cyst depth from Descemet's layer was 261.7 ± 222.7 μm with a mean corneal button thickness of 474.2 ± 126.6 μm. <b>Conclusions</b>: Acanthamoeba cysts were found to penetrate deeper within the cornea amongst patients that underwent an emergent TPK compared to patients that underwent an elective OPK/DALK. This may suggest an association between Acanthamoeba cyst depth and infection severity and provides valuable clinical insights towards understanding factors such as infection recurrence and resistance to treatment.