Quantitative Analysis of Depth, Distribution and Density of Cysts in Acanthamoeba Keratitis using Confocal Microscopy

Abstract

Purpose : To quantify the density, distribution and depth of invasion of cysts in the corneas of eyes with Acanthamoeba Keratitis (AK) by in-vivo confocal microscopy (IVCM) using a novel scanning pattern.

Methods : Patients with clinically diagnosed AK underwent IVCM ((HRT III RCM, Heildelberg, Germany) at various time points during the clinical course. Five locations of the cornea were scanned: the clinically affected area, as well as four standard points on the peripheral cornea corresponding to temporal, nasal, inferior, and superior locations. The IVCM scans were then manually graded by trained reading center graders to quantify the maximum depth of invasion and density of cysts (per mm²) in each of the five locations.

Results : Seventeen eyes of 14 patients with visible cysts on IVCM were included. Cultures were positive for Acanthamoeba in 9 eyes (52.9%). IVCM confirmed the diagnosis of AK in the absence of positive cultures in 8 eyes (47.1%). Mean cyst density at presentation was 215/mm² (range, 64-484), and average cyst depth was 169 microns (range, 70-300) in the affected area. Fourteen eyes, with maximum cyst depth of 200 microns or less, reached clinical resolution with medical treatment alone. The mean cyst density became zero at the final visit in these 14 eyes. Three eyes that ultimately underwent therapeutic PKP had cysts in all four quadrants with deeper cyst infiltration; the average cyst depth in these corneas was 283.3microns (range, 250-300).In one of these3 eyes, preoperatively, IVCM identified cysts extending to the limbus; postoperatively, AK is not resolved and IVCM demonstrates cysts within the graft host interface.

Conclusions : IVCM is clinically useful for the diagnosis of AK. Acanthamoeba cyst density, distribution and depth of invasion can be quantified non-invasively using IVCM, using a scanning approach including both central and peripheral locations to detect cysts that may otherwise be missed in routine scanning patterns. These parameters may be employed in prognostication and treatment decision-making in AK. A broader and deeper distribution of cysts on IVCM appears to portend a worse prognosis.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

In vivo laser confocal microscopy of Acanthamoeba Keratitis showed double-walled cysts (arrow) and a number of highly reflective, high-contrast round-shaped particles 10–15 μm in diameter (arrow head), suggestive of Acanthamoeba cysts.