Biomedical Engineering, University of California, Irvine, Irvine, CA, United States.
Ophthalmology, University of California, Irvine, Irvine, CA, United States.
Exp Eye Res. 2018 Dec;177:173-180. doi: 10.1016/j.exer.2018.08.009. Epub 2018 Aug 14.
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-riboflavin induced corneal collagen crosslinking (UVA CXL) on collagen structure. Two groups, four rabbits each, were treated in the right eye with standard UVA CXL. In vivo confocal microscopy was performed at 1, 2, and 4 weeks after treatment for the first group and up to three months for the second group to measure epithelial/stromal thickness and corneal haze during recovery. Rabbits were sacrificed at one and three months, respectively, and their corneas fixed under pressure. Regions of crosslinking were identified by the presence of collagen autofluorescence (CAF) and then collagen structure was imaged using SHG microscopy. The degree of CFC was determined by measuring the percentage difference between the length of the collagen fiber and the linear distance traveled. CFC was measured in the central anterior and posterior CXL region, the peripheral non-crosslinked region in the same cornea, and the central cornea of the non-crosslinked contralateral eye. No change in corneal thickness was detected after one month, however the stromal thickness surpassed its original baseline thickness at three months by 25.9 μm. Corneal haze peaked at one month and then began to clear. Increased CAF was detected in all CXL corneas, localized to the anterior stroma and extending to 42.4 ± 3.4% and 47.7 ± 7.6% of the corneal thickness at one and three months. There was a significant (P < 0.05) reduction in CFC in the CAF region in all eyes averaging 1.007 ± 0.006 and 1.009 ± 0.005 in one and three month samples compared to 1.017 ± 0.04 and 1.016 ± 0.06 for controls. These results indicate that there is a significant reduction in collagen crimping following UVA CXL of approximately 1%. One possible explanation for this loss of crimping could be shortening of the collagen fibers over the CXL region.
本研究旨在通过检测二次谐波产生（SHG）信号的非线性光学成像来测量胶原纤维卷曲（CFC），以确定 UVA-核黄素诱导的角膜胶原交联（UVA CXL）对胶原结构的影响。两组各四只兔子右眼接受标准 UVA CXL 治疗。第一组在治疗后 1、2 和 4 周进行共焦显微镜检查，第二组在 3 个月内进行共焦显微镜检查，以测量上皮/基质厚度和恢复过程中的角膜混浊。兔子分别在 1 个月和 3 个月时处死，其角膜在压力下固定。通过胶原自发荧光（CAF）的存在识别交联区域，然后使用 SHG 显微镜对胶原结构进行成像。通过测量胶原纤维长度与线性距离之间的百分比差异来确定 CFC 的程度。在中央前和后 CXL 区域、同一角膜的周围非交联区域以及非交联对侧眼的中央角膜测量 CFC。一个月后，角膜厚度没有变化，但三个月后基质厚度比原始基线厚度增加了 25.9μm。角膜混浊在一个月时达到峰值，然后开始消退。所有 CXL 角膜均检测到 CAF 增加，局限于前基质，一个月和三个月时分别增加到角膜厚度的 42.4±3.4%和 47.7±7.6%。所有眼睛的 CAF 区域的 CFC 均显著（P<0.05）减少，与对照相比，一个月和三个月的样本分别平均减少 1.007±0.006 和 1.009±0.005，而对照分别减少 1.017±0.04 和 1.016±0.06。这些结果表明，UVA CXL 后胶原卷曲显著减少约 1%。这种卷曲丧失的一个可能解释是交联区域内胶原纤维缩短。
