Host Response and Pathogen Load in Acanthamoeba Keratitis: A Histopathological Analysis

The purpose of this study was to evaluate the histopathological features of Acanthamoeba keratitis (AK) and correlate organism morphology, distribution, and density with inflammatory response and clinical parameters in surgically managed cases.

This retrospective case series included all histopathologically confirmed cases of AK that underwent therapeutic penetrating keratoplasty (TPK). Demographic, clinical, microbiological, and histopathological data were analyzed. Histologic evaluation included organism type (cyst or trophozoite), density, stromal location, inflammatory pattern, and surgical margin status. Associations between these features were assessed using Fisher's exact and Mann-Whitney U tests.

Twenty-three eyes of 23 patients (mean age = 44.3 ± 14.6 years, 65.2% male patients) were analyzed. The median duration from symptom onset to TPK was 47 days (interquartile range [IQR] = 32.5-65.5 days). Preoperative microbiological detection of Acanthamoeba was achieved in 60.8% of cases. Cystic forms predominated histologically (56.5%), with diffuse stromal involvement in 56.5% and acute inflammation in 60.9% of specimens. Acute inflammation was more frequent in eyes with severe organism load (87.5% vs. 46.7%, P = 0.056). Patients with diffuse infection were significantly younger than those with localized involvement (34.2 ± 3.9 vs. 47.8 ± 15.4 years, P = 0.047). Margin positivity (30.4%) did not correlate with severity or recurrence. Postoperative recurrence occurred in three cases (13%), independent of organism or host factors.

AK demonstrates marked variability in both organism distribution and host inflammatory response. Tissue damage appears to be more immune-mediated than organism load-dependent. Younger patients tended to show diffuse stromal involvement. Persistent cyst formation underlies recurrence, underscoring the importance of early diagnosis and prolonged postoperative anti-amoebic therapy.