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Catherine Marando, Choul Yong Park, Jason A. Liao, Jimmy K Lee, Roy S Chuck; Revisiting the Cornea and Trabecular Meshwork Junction with Two Photon Excitation Fluorescence Microscopy. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5670.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the collagen and elastin architecture at the junction of the human cornea and trabecular meshwork (TM). Clinically, this is relevant because studies have demonstrated a risk for glaucoma post penetrating keratoplasty (PKP). Surgically, during Descemet’s membrane endothelial keratoplasty (DMEK) graft preparation, careful attention is given to peripheral cornea in order to prevent radial tears. Histologically, this junction has been of increased interest due to debate over Dua’s layer.
The cornea, TM, and ciliary body (CB) tendons of five unfixed human corneal buttons were imaged with an inverted two-photon excited fluorescence microscope (FluoView FV-1000, Olympus, Central Valley, PA). The laser (Ti :Sapphire) was tuned at 850nm for two photon excitation. Backscatter signals of second harmonic generation (SHG) and autofluorescence (AF) were collected through a 425/30nm emission filter and a 525/45 emission filter, respectively. The SHG signal corresponds to collagen fibers and the AF signal corresponds to elastin-containing tissue. Tissue structure representations were obtained via software generated reconstructions of consecutive and overlapping (z-stack) images through the relevant sample depth.
Collagen rich CB tendons insert into the cornea between Descemet’s membrane (DM) and posterior stroma along with elastin fibers originating from TM. The CB tendons directly abut DM and their insertion narrows as they course centrally in the cornea, giving a wedge appearance to these parallel collagen fibers. Approximately 260μm centrally from the edge of DM, the CB tendons fan out and merge with pre-DM collagens. As the CB tendons enter the cornea, they form a dense collagenous comb-like structure orthogonal to the edge of DM and supported by a delicate elastin network of interwoven fibers originating from TM.
Two-photon excited fluorescence microscopy has improved our understanding of peripheral corneal architecture. We find no histologic support for a distinct 10μm thick Dua’s layer continuous with DM in the periphery. Our findings that CB tendons attach to pre-DM collagen and are supported by a fine TM elastin network may guide studies examining the effect of corneal surgery involving pre-DM collagens on glaucoma incidence. Comb-like CB tendon insertions in this region may contribute to the radial tears encountered when preparing DMEK grafts.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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