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Michele Pascolini, Mattia Minozzi, Federico Carraro, Nicola Codogno, Ronnye Pajaro, Christian Tiso, Simone Pajaro, Cesare Tanassi; Non-contact laser confocal microscope for corneal imaging. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2123. doi: https://doi.org/.
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Confocal microscopy is an appealing technique for the direct observation of corneal pathologies. Previous approaches were either uncomfortable for the patient or lacking image quality. We prototyped a non-contact laser confocal microscope (CS-5) with an unprecedented resolution from the epithelium to the endothelium.
CS-5 takes 1-Mpixel images at 18 fps with a Field of View of 400x400 µm2 at a distance of 12 mm from the patient’s corneal apex. In such conditions, the cornea itself and the air gap between eye and device significantly degrade the imaging performances. That’s why non-contact microscopes limit their observation to the endothelium. To observe other layers, microscopes need to work in contact with the cornea.Despite its simple design, CS-5 is able to acquire non-contact images from endothelium to epithelium because it provides a very effective confocality in the cornea. It is based on a 2D scanning head and on two micrometric circular apertures whose dimensions have been studied to avoid reflections from the epithelium and obtain sharp images of the layers. A red laser source propagates light through a single-mode fiber to obtain a homogenous illumination aperture. The signal is collected by an Avalanche Photo-Diode connected to carefully designed electronics that combines high gain and low noise. A real-time preprocessing shows live images to drive the alignment and the acquisition.
We tested the CS-5 on healthy patients. The incident laser power was ranging from 0.08 mW for endothelium and stroma down to 8 μW for the epithelium. Patients were required to look straight and the alignment was manually performed. Acquired images show the nuclei of the endothelial cells, posterior and anterior stroma, sub-basal nerve plexus, basal cells and tear film, whose in-depth evolution can be tracked with an axial resolution lower than 1 µm. Raw images present good resolution but are crispy because of the laser source.
The CS-5 is a novel corneal confocal microscope that operates in non-contact conditions to improve the comfort for the patient and avoid sterilization issues. Image quality is comparable with contact microscopes and should be furthermore increased by processing. The 3D evolution of the layers is clearly visible and pave the way for stacking algorithms for a better exam analysis.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Corneal layers from the endothelium to the epithelium acquired on healthy patients.
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