Department of Ophthalmology, University of Würzburg, Würzburg, Germany.
Invest Ophthalmol Vis Sci. 2010 Aug;51(8):3929-34. doi: 10.1167/iovs.09-4524. Epub 2010 Mar 5.
Riboflavin/ultraviolet A (UVA) cross-linking (CXL) of corneal collagen is a novel method of stabilizing corneal mechanical properties and preventing progression of keratectasias. This study was conducted to investigate whether CXL influences ablation rate, flap thickness, and refractive results of excimer laser procedures ex vivo.
Corneal epithelium was removed from enucleated porcine eyes, and CXL was performed with riboflavin 0.1% and UVA radiation (365 nm, 3 mW/cm(2)) for 30 minutes. Control eyes received epithelial abrasion only. Diffusion of riboflavin through the cornea was assessed by using infrared-excited, two-photon microscopy of riboflavin autofluorescence, combined with second-harmonic generation of fibrillar collagen. During phototherapeutic keratectomy, corneal thickness was measured by optical coherence pachymetry. During LASIK for myopia, the flap thickness of microkeratome cuts was measured and the induced refractive change assessed by Placido topography. Data were analyzed by Shapiro-Wilk test and Student's t-test.
Multiphoton imaging showed a rapid (30-minute) and even distribution of riboflavin throughout the corneal stroma. No difference in ablation rate was measured in treated and untreated corneas (P = 0.90). Mean flap thickness was increased by 44% in cross-linked corneas (P < 0.01). After LASIK for myopia of 4 to 25 D, the mean corneal refractive change was reduced in CXL-treated eyes by 20.1% (P < 0.05). This effect was less pronounced in thinner flaps.
CXL reduces the amount of refractive change after LASIK for myopia. Although the laser ablation rate is unaffected, CXL results in an increased flap thickness. This study suggests the need for adjustment of microkeratome and laser parameters for LASIK after CXL and indirectly endorses the theory of a direct stiffening effect of CXL.
核黄素/长波紫外线（UVA）交联（CXL）角膜胶原是稳定角膜机械性能和阻止角膜扩张进展的一种新方法。本研究旨在探讨 CXL 是否会影响准分子激光手术的消融速率、瓣厚度和屈光结果。
从猪眼眼球中去除角膜上皮，用核黄素 0.1%和 UVA 辐射（365nm，3mW/cm²）进行 30 分钟 CXL。对照眼仅接受上皮擦伤。通过使用红外激发的双光子显微镜观察核黄素自发荧光，结合纤维胶原的二次谐波产生，评估核黄素在角膜中的扩散。在光性角膜切削术中，通过光学相干断层扫描测量角膜厚度。在近视 LASIK 中，测量微型角膜刀切割的瓣厚度，并通过 Placido topography 评估诱导的屈光变化。数据采用 Shapiro-Wilk 检验和 Student's t 检验进行分析。
多光子成像显示核黄素在角膜基质中快速（30 分钟）且均匀分布。处理和未处理的角膜之间的消融速率无差异（P=0.90）。交联角膜的平均瓣厚度增加了 44%（P<0.01）。对于近视 4 至 25D 的 LASIK，CXL 治疗眼的角膜屈光变化平均减少 20.1%（P<0.05）。在较薄的瓣中，这种效果不那么明显。
CXL 可减少 LASIK 治疗近视后的屈光变化量。尽管激光消融速率不受影响，但 CXL 会导致瓣厚度增加。本研究表明需要调整 CXL 后的微型角膜刀和激光参数进行 LASIK，并间接支持 CXL 具有直接增强效果的理论。
