Femtosecond-Laser-based crosslinking of corneal collagen fibers.

角膜胶原纤维的交联化提供了特定改变眼睛生物力学的可能性。除了治疗屈光手术后的圆锥角膜和继发性角膜扩张外，屈光矫正和预防近视也是潜在的应用领域。为了稳定圆锥角膜和继发性角膜扩张症的角膜，临床上使用了UV(A)-核黄素交联剂。也有第一批动物实验表明，原则上可以通过巩膜交联来防止近视的发展。在UV(A)-核黄素交联中，核黄素被局部应用，并通过UV(A)辐射进行交联。虽然该手术在临床上原则上是有效的，但精确度较低，因此无法对病变区域进行单独治疗或进行有针对性的屈光矫正。此外，必要的上皮磨损和相关的角膜敏感度增加会导致患者疼痛，也可能是感染源。飞秒激光作为眼科手术切割工具获得了巨大的成功。一种不含化学物质的激光方法对角膜交联化也有很大的医疗价值。最近有研究表明，使用飞秒激光脉冲可以在没有化学试剂的情况下使角膜胶原纤维交联化。这使得在小鼠动物模型中矫正近视成为可能。其作用机制被认为是激光诱导的等离子体产生的活性氧物种以及随后的胶原纤维的交联性。在这一应用中，通过多光子激发直接激发氨基酸是有利的。根据已发表的胶原结构和涉及的氨基酸的光化学性质以及我们自己的实验数据，有证据表明胶原纤维直接交联化是可能的。该项目的总体目标是通过直接激发相关氨基酸来研究角膜交联性，并对其转化为临床应用进行评估。为此，定义了3个工作目标：1.定义用于交联性角膜组织的激光参数，并建立描述该过程的速率方程模型；2.建立用于分析角膜交联性和评估组织生物学效应的方法学平台；3.通过与金标准UV(A)核黄素交联剂进行比较，评估该方法的翻译潜力。这将使一种新的无试剂的FS-激光手术成为可能，用于治疗圆锥角膜、继发性角膜扩张和近视。

Cross-linking of corneal collagen fibers offers the possibility of specifically modifying the biomechanics of the eye. In addition to the treatment of keratoconus and secondary keratectasia after refractive surgery, refractive correction and prevention of myopia are also potential fields of application. To stabilize the cornea in keratoconus and secondary keratectasia, UV(A)-riboflavin cross-linking is used clinically. There are also first animal experiments which show that it is in principle possible to prevent the development of myopia through scleral cross-linking. In UV(A)-riboflavin cross-linking, riboflavin is applied locally and cross-linked by UV(A) radiation. Although the procedure is clinically effective in principle, the precision is low, so that the exclusive treatment of diseased regions or targeted refraction correction is not possible. In addition, the necessary abrasion of the epithelium and the associated increase in corneal sensitivity leads to pain for the patient and is a possible source of infection. Femtosecond-(fs)-lasers are used with great success as surgical cutting tools in ophthalmology. A laser method without chemicals would also be of great medical benefit for corneal cross-linking. It has recently been shown that corneal collagen fibers can be cross-linked without chemical agents using fs-laser pulses. This made it possible to correct myopia in a murine animal model. The mechanism of action is postulated to be the production of reactive oxygen species by the laser-induced plasma and the subsequent cross-linking of the collagen fibers. In this application the direct excitation of the amino acid via multiphoton excitation is favoured. Based on the published collagen structure and the photochemical properties of the amino acids involved as well as our own experimental data, there is evidence that direct cross-linking of collagen fibers is possible. This is expected to lead to higher specificity, precision and fewer side effects.The overall aim of the proposed project is to investigate corneal cross-linking by direct excitation of the relevant amino acids and to evaluate the translation into clinical application. To this end, 3 working objectives are defined: 1. Definition of the laser parameters for cross-linking corneal tissue and development of a rate equation model to describe the processes;2. Establishment of a methodological platform for the analysis of corneal cross-linking and evaluation of biological effects on tissue;3. Evaluation of the translational potential of the procedure by comparison with the gold standard UV(A) riboflavin crosslinking.This could enable a new agent-free fs-laser procedure for the treatment of keratoconus, secondary keratectasia and myopia.