Kohlhaas Markus, Spoerl Eberhard, Schilde Thomas, Unger Gabriele, Wittig Christine, Pillunat Lutz E
Department of Ophthalmology, Universitätsklinikum CGC, Dresden, Germany.
J Cataract Refract Surg. 2006 Feb;32(2):279-83. doi: 10.1016/j.jcrs.2005.12.092.
To examine to which depth of the cornea the stiffening effect is biomechanically detectable.
Department of Ophthalmology, University of Dresden, Dresden, Germany.
Of 40 enucleated porcine eyes, 20 eyes were treated with the photosensitizer riboflavin (0.1%) and ultraviolet A (UVA) light (370 nm, 3 mW/cm2, 30 minutes); the other 20 eyes served as control. From each eye, 2 flaps of 200 microm thickness were cut with a microkeratome, and strips of 5 mm width and 7 mm length were prepared. Stress-strain behavior was measured with a material tester to characterize the stiffening effect. Five pairs of human donor eyes were tested in the same way.
In porcine corneas, the stiffening effect was stronger in the anterior-treated flaps than in the posterior-treated flaps and the control flaps (P = .001). A 5% strain was achieved at a stress of 261.7 +/- 133.2 x 10(3) N/m2 in the anterior-treated flaps and 104.1 +/- 52.7 x 10(3) N/m2 in the anterior control flaps. The posterior-treated flaps (105.0 +/- 55.8 x 10(3) N/m2) and the posterior control flaps (103.7 +/- 61.8 x 10(3) N/m2) showed no difference (P = .95). A similar stiffening effect was observed in human eyes, but contrary to findings in porcine corneas, in human corneas the anterior control flaps were stiffer than the posterior control flaps (P = .027).
Treatment of the cornea with riboflavin and UVA significantly stiffened the cornea only in the anterior 200 microm. This depth-dependent stiffening effect may be explained by the absorption behavior for UVA in the riboflavin-treated cornea. Sixty-five percent to 70% of UVA irradiation was absorbed within the anterior 200 microm and only 20% in the next 200 microm. Therefore, deeper structures and even the endothelium are not affected.
研究在生物力学上可检测到角膜硬化效应的深度。
德国德累斯顿市德累斯顿大学眼科。
在40只摘除的猪眼中，20只眼用光敏剂核黄素（0.1%）和紫外线A（UVA）光（370纳米，3毫瓦/平方厘米，30分钟）进行处理；另外20只眼作为对照。用微型角膜刀从每只眼中切下两片厚度为200微米的瓣片，并制备宽度为5毫米、长度为7毫米的条带。用材料测试仪测量应力-应变行为以表征硬化效应。对5对人类供体眼进行了同样的测试。
在猪角膜中，前处理瓣片的硬化效应强于后处理瓣片和对照瓣片（P = 0.001）。在前处理瓣片中，在应力为261.7±133.2×10³牛/平方米时达到5%的应变，在前对照瓣片中为104.1±52.7×10³牛/平方米。后处理瓣片（105.0±55.8×10³牛/平方米）和后对照瓣片（103.7±61.8×10³牛/平方米）无差异（P = 0.95）。在人眼中观察到类似但相反的硬化效应，在猪角膜中，前对照瓣片比后对照瓣片更硬（P = 0.027）。
用核黄素和UVA处理角膜仅在前200微米处显著使角膜变硬。这种深度依赖性硬化效应可能由核黄素处理的角膜中UVA的吸收行为来解释。65%至70%的UVA照射在前200微米内被吸收，在接下来的200微米内仅20%被吸收。因此，更深层结构甚至内皮不受影响。
