In vivo confocal microscopy morphological features and cyst density in Acanthamoeba keratitis: Confocal microscopy morphology in Acanthamoeba keratitis

Purpose: To correlate in vivo confocal microscopy morphological features (IVCM-MF) and Acanthamoeba cyst density (ACD) with final best corrected visual acuity (BCVA) in Acanthamoeba keratitis (AK). Design: Retrospective cohort study. Methods: Patient demographics, treatment outcome, and corresponding IVCM-MF performed at the acute stage of infection were analysed. Inclusion criteria were microbiological positive AK cases seen at Moorfields Eye Hospital between February 2013 and October 2017. Statistical significance was assessed by multinomial regression and multiple linear regression analysis. Main outcome measures were final BCVA. Results: A total of 157 eyes (157 patients) had AK. Absence of single file of round/ovoid objects was associated with a BCVA of 6/36 to 6/9 (OR 8.13; 95% CI, 1.55-42.56, P = 0.013) and ≥ 6/6 (OR 10.50; 95% CI, 2.12-51.92, P = 0.004) when compared to NPL to 6/60. Absence of rod/spindle objects was associated with a BCVA of ≥ 6/6 (OR 4.55; 95% CI, 1.01-20.45, P = 0.048). Deep stromal/ring infiltrate was associated with single file round/ovoid objects (OR 7.78; 95% CI, 2.69-22.35, P < 0.001), rod/spindle objects (OR 7.05; 95% CI, 2.11-23.59, P = 0.002), and binary round/ovoid objects (OR 3.45; 95% CI, 1.17-10.14, P = 0.024). There was a positive association between ACD with treatment duration (β = 0.14, P = 0.049), number of IVCM-MF (β = 0.34, P = 0.021) and clusters of round/ovoid objects (β = 0.29, P = 0.002). Conclusions: Specific IVCM-MF correlate with ACD and clinical staging of disease, and are prognostic indicators for a poorer visual outcome.