In vivo Confocal Microscopy of Acanthamoeba Keratitis

Abstract

Purpose: : Acanthamoeba keratitis is a corneal infection caused by a free-living amoeba. The incidence of Acanthamoeba keratitis is estimated to be approximately 1.65 to 2.01 per million contact lens wearers. Aim of the study was to evaluate the corneal changes of the subepithelial nerve plexus in patients affected by Acanthamoeba keratitis through the in vivo confocal microscope (Confoscan 4, NIDEK Technologies).

Methods: : 10 patients ( 8 females and 2 males) with Acanthamoeba keratitis ( mean age 25,83±9,68; range 19 to 34 ) affected by Acanthamoeba keratitis were included in this study. 9 of them had monolateral keratitis ( 6 in the left eye and 3 in the right eye) and only one patient had a bilateral keratitis, therefore 11 eyes were included in the study.Diagnosis of Acanthamoeba was based on clinical history, corneal scraping and identification of cyst with confocal microscopy.evaluation. Following detailed explanation and acquisition of informed verbal consent, slit-lamp biomicroscopy and photography and in vivo confocal microscopy (Confoscan 4, NIDEK Technologies ) were performed in the involved eye. Each examination was evaluated with a frame by frame manner by one examinator (MP). Data from normal patients wearing contact lenses who were age-matched to the patients were used as a control for analysis.

Results: : At the slit lamp examination 6 of the 11 eyes presented with peripheral neuritis. In the same day all patients underwent confocal microscopy examination and all 11 eyes presented with enlarged nerve fibers with loss of beadings and reduction of nerves branching. All nerves of patients affected by Acanthamoeba keratitis were surrounded by a sheet with increased reflectivity, while the nerves itselfes showed a lower reflectivity, no beadings, a mostly linear shape and a decrease in the number of branching. Also the diameter of the nerves was enlarged. In the control group of non affected contact lens wearers an increase in tortuosity and number of vescicoles of the nerves were noticed also when compared to a normal population of non contact lens wearers.

Conclusions: : It seems notable that nerve changes occurred also in patients affected by Acanthamoeba keratitis with no clinical evidence of neuritis. This study suggests that Acanthamoeba involves the subbasal nerve plexus in early stages of the disease and in 100% of the patients.

Keywords: Acanthamoeba • imaging/image analysis: clinical • microscopy: confocal/tunneling