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Samantha Bradford, Eric R Mikula, Tibor Juhasz, Donald J. Brown, James Jester; Collagen fiber crimping following in vivo UVA-induced corneal crosslinking (CXL). Invest. Ophthalmol. Vis. Sci. 2017;58(8):5566.
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© ARVO (1962-2015); The Authors (2016-present)
While studies have shown that UVA CXL induces mechanical stiffening of the cornea, less is known regarding changes in the collagen fiber organization. The purpose of this study was to measure collagen fiber crimping (CFC) using nonlinear optical imaging of second harmonic generated (SHG) signals to determine the effects of UVA CXL on collagen structure.
One cornea per rabbit was treated with standard Dresden UVA CXL. In vivo confocal microscopy was performed at 7, 14, and 28 days after treatment to measure epithelial/stromal thickness and position of demarcation line (DL or transition between acellular anterior and untreated posterior stroma) during recovery. Rabbits were sacrificed at six weeks and their corneas fixed under pressure (20mmHg) with 2% paraformaldehyde. Corneas were then vibratome sectioned (250µm) and collagen organization from the peripheral to central cornea was imaged using SHG microscopy. Regions of CXL were identified by the presence of collagen autofluorescence (CAF), which was localized to the central anterior stroma. The degree of CFC was then determined by measuring the percentage difference between the length of the collagen fiber and the linear distance traveled. CFC was measured in the anterior corneal CXL region, the posterior non-CXL region, the non-CXL peripheral region in the same cornea, and the central cornea of the non-CXL contralateral eye.
No change in corneal thickness was detected from 7-28 days, however there was a significant decrease in the depth of DL from 175.9±25.7µm to 126.8±28.3µm (P<0.001). Increased CAF was detected in all CAL corneas, localized to the anterior stroma and extending to a depth of 140.9±27.5µm. CFC measurements in regions showing no CAF showed no significant differences and ranged from 1.7±0.4% in the control corneas, 1.7±0.1% in the peripheral CXL corneas and 1.9±0.7% in the central, posterior stroma underlying the CAF region. There was a significant (P<0.05) reduction in CFC in the CAF region in all eyes averaging 0.67±0.58%.
These results indicate that there is a significant reduction in collagen crimping following UVA CXL of approximately 1%. This loss of crimping may be due either to shortening of the collagen fibers over the CAL region, or due to the resistance of fiber relaxation after corneal removal.
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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