Levy Alexander M, Fazio Massimo A, Grytz Rafael
Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, USA.
Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, USA.
Ophthalmic Physiol Opt. 2018 May;38(3):246-256. doi: 10.1111/opo.12454.
Myopia progression is thought to involve biomechanical weakening of the sclera, which leads to irreversible deformations and axial elongation of the eye. Scleral crosslinking has been proposed as a potential treatment option for myopia control by strengthening the mechanically weakened sclera. The biomechanical mechanism by which the sclera weakens during myopia and strengthens after crosslinking is not fully understood. Here, we assess the effect of lens-induced myopia and exogenous crosslinking using genipin on the inelastic mechanical properties of the tree shrew sclera measured by cyclic tensile tests.
Cyclic tensile tests were performed on 2-mm wide scleral strips at physiological loading conditions (50 cycles, 0-3.3 g, 30 s cycle ). Two scleral strips were obtained from each eye of juvenile tree shrews exposed to two different visual conditions: normal and 4 days of monocular -5 D lens wear to accelerate scleral remodelling and induce myopia. Scleral strips were mechanically tested at three alternative conditions: immediately after enucleation; after incubation in phosphate buffered saline (PBS) for 24 h at 37°C; and after incubation for 24 h in PBS supplemented with genipin at a low cytotoxicity concentration (0.25 mm). Cyclic softening was defined as the incremental strain increase from one cycle to the next.
-5D lens treatment significantly increased the cyclic softening response of the sclera when compared to contralateral control eyes (0.10% ± 0.029%, mean ± standard error, P = 0.037). Exogenous crosslinking of the lens treated sclera significantly decreased the cyclic softening response (-0.12% ± 0.014%, P = 2.2 × 10 ). Contrary to all other groups, the genipin-cross-linked tissue did not exhibit cyclic softening significantly different from zero within the 50-cycle test.
Results indicated that cyclic tensile loading leads to an inelastic, cyclic softening of the juvenile tree shrew sclera. The softening rate increased during lens-induced myopia and was diminished after genipin crosslinking. This finding suggests that axial elongation in myopia may involve a biomechanical weakening mechanism that increased the cyclic softening response of the sclera, which was inhibited by scleral crosslinking using genipin.
近视进展被认为涉及巩膜生物力学减弱，这会导致眼睛不可逆变形和眼轴伸长。巩膜交联已被提议作为一种通过强化机械性减弱的巩膜来控制近视的潜在治疗选择。近视期间巩膜如何减弱以及交联后如何强化的生物力学机制尚未完全明了。在此，我们使用京尼平评估晶状体诱导性近视和外源性交联对通过循环拉伸试验测量的树鼩巩膜非弹性力学性能的影响。
在生理负荷条件下（50个循环，0 - 3.3克，每个循环30秒）对2毫米宽的巩膜条进行循环拉伸试验。从暴露于两种不同视觉条件的幼年树鼩的每只眼睛获取两条巩膜条：正常条件以及单眼佩戴 -5D镜片4天以加速巩膜重塑并诱导近视。在三种不同条件下对巩膜条进行力学测试：摘除眼球后立即测试；在37°C下于磷酸盐缓冲盐水（PBS）中孵育24小时后测试；以及在低细胞毒性浓度（0.25毫米）的添加了京尼平的PBS中孵育24小时后测试。循环软化定义为从一个循环到下一个循环的应变增量增加。
与对侧对照眼相比，-5D镜片处理显著增加了巩膜循环软化反应（0.10% ± 0.029%，平均值 ± 标准误，P = 0.037）。经镜片处理的巩膜进行外源性交联显著降低了循环软化反应（-0.12% ± 0.014%，P = 2.2×10）。与所有其他组相反，在50个循环测试中，经京尼平交联的组织未表现出与零有显著差异的循环软化。
结果表明，循环拉伸负荷导致幼年树鼩巩膜出现非弹性、循环软化。在晶状体诱导性近视期间软化速率增加，而在京尼平交联后降低。这一发现表明，近视中的眼轴伸长可能涉及一种生物力学减弱机制，该机制增加了巩膜的循环软化反应，而使用京尼平进行巩膜交联可抑制这种反应。
