Purpose:
To investigate the utility of high-resolution OCT for imaging Acanthamoeba organisms in keratitis cases.
Methods:
A high-speed Fourier-domain optical coherence tomography (FD-OCT) system (RTVue, Optovue, Inc.) with a corneal adaptor module (CAM) was used for imaging, with an axial resolution of 5 µm. The short high-resolution objective lens provided a transverse resolution of 5 µm. 3 patients with Acathamoeba keratitis seen at Doheny Eye Institute, University of Southern California, from June 2005-present were studied. Patients underwent slit lamp biomicroscopy, confocal microscopy (Confoscan 4, Nidek), and OCT imaging. OCT imaging was also performed in vitro on slides using Acanthamoeba organisms inoculated in 0.25% agar.
Results:
Acanthamoeba cysts were visualized by OCT as highly reflective spots in vitro (Figure). Based on in vitro OCT images, the diameter of Acanthamoeba cysts ranges from 20-30 µm. In 1 effectively treated case, OCT showed no evidence of cysts, corroborated by the clinical exam and negative confocal scan. In 2 active keratitis cases, cysts were visualized by confocal microscopy but not OCT. OCT visualization of Acanthamoeba was hampered by the highly reflective scarring and infiltrate in these cases of stromal keratitis.
Conclusions:
This is the first demonstration of in vitro visualization of Acanthamoeba with OCT. The visualization of infectious microorganisms is an additional application for OCT, which already has many uses in posterior and anterior segment imaging. In the first in vivo tests, we found that masking of small organisms by concurrent inflammation and scarring is a limitation. It remains to be seen whether OCT could be used to visualize Acanthamoeba better in early epithelial keratitis where the cornea is relatively clear.
Figure. OCT of cultured Acanthamoeba suspended in 0.25% agar.
Keywords: Acanthamoeba • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • keratitis