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Timothy D Weber, Jerome Mertz; Non-contact in vivo corneal microscopy with asymmetric fundus retroillumination. Invest. Ophthalmol. Vis. Sci. 2020;61(9):PP005.
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Cellular-resolution corneal imaging is a useful tool for noninvasive disease diagnostics and treatment monitoring. Still many subjects cannot tolerate the usual contact operation (i.e. the objective lens is placed in contact with the cornea), and this has fueled recent interest in non-contact alternatives. Existing techniques are all based on reflected light and therefore require a high degree of optical sectioning in order to reject much stronger reflections originating at other surfaces, such as the air-cornea interface. Here we present an alternative approach based on obliquely transmitted light, which produces phase-gradient contrast images of the cornea across a 1-mm field of view.
Our method, shown conceptually in Figure 1(A), uses reflected light from the fundus to transilluminate the cornea. We project the light on the fundus such that the reflected light obliquely back-illuminates the cornea. Asymmetric illumination is a simple way to convert phase-only objects (like the cornea) into intensity contrast, recordable on a camera. We call this method asymmetric fundus retroillumination microscopy, in homage to the related slit lamp technique. A detailed optical diagram is also given in Figure 1(B).
We imaged 3 healthy volunteers ranging in age from 26 to 58 and with varying fundus pigmentation. For each subject, informed consent was obtained prior to imaging. The research was approved by the Boston University Institutional Review Board and conformed to the principles stated in the Declaration of Helsinki. Figure 2 shows a few example images that we have obtained with the retroillumination microscope. We can routinely image layers of cells in the epithelium, the sub-basal nerve plexus, large stromal nerves, and the endothelium. Additionally, we have imaged the crystalline lens epithelium and anterior fibers.
We have introduced a new technique for corneal microscopy based on fundus reflection. The technique is based on relatively inexpensive instrumentation and unlike other techniques, our method uses transmitted light, which produces different, but complimentary image contrast.
This is a 2020 Imaging in the Eye Conference abstract.
A: corneal retroillumination microscopy concept. B: detailed system schematic.
A: sub-basal nerve plexus, B: basal epithelial cell layer, C: dendritic immune cells, D: large stromal nerve, E: endothelium, nuclei are visible. Scale bars: 50 um.
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