Bachmann W, Jean B, Bende T, Seiler T, Hibst R, Thiel H J
University Eye Hospital, Tuebingen, Germany.
Refract Corneal Surg. 1992 Sep-Oct;8(5):363-7.
Topometry and measurement of photoablation patterns are key questions for keratorefractive photoablation. Ablation rates have been determined previously by either tissue perforation or by micrometry performed on histologic sections.
A three-dimensional cast of cornea after irradiation was made by using a two-component silicon gel that polymerizes within minutes, thus preserving the corneal topography immediately after photoablation. Polymerization is athermal and nontoxic. The resulting silicon blocks were cut perpendicularly to the anterior surface and measured by calibrated light microscopy.
The silicon surface is extremely smooth and the accuracy of the cast is better than 0.25 micron. Reproducibility and long-term stability were demonstrated for casts of photoablated polymethylmethacrylate. Thus, ablation rates and profile, volumetry, and topometry can be determined following laser ablation. The method has been applied for 193-nanometer excimer laser in vitro irradiation of the human cornea. Ablation rates in Bowman's layer and stroma for various radiant energies and distinct pulse numbers were found to be in agreement with published data, and an incubation effect for the first laser pulses could be demonstrated.
The method is nondestructive, accurate, inexpensive, practical, and reduces requirements for laboratory animals.
角膜屈光性光消融的角膜地形图测量和光消融模式测量是关键问题。消融率此前已通过组织穿孔或对组织学切片进行测微法来确定。
使用一种在数分钟内聚合的双组分硅胶制作照射后角膜的三维铸型，从而在光消融后立即保留角膜地形图。聚合是无热且无毒的。将所得的硅胶块垂直于前表面切割，并通过校准的光学显微镜进行测量。
硅胶表面极其光滑，铸型的精度优于0.25微米。已证明光消融的聚甲基丙烯酸甲酯铸型具有可重复性和长期稳定性。因此，在激光消融后可以确定消融率、轮廓、体积测量和角膜地形图。该方法已应用于193纳米准分子激光对人角膜的体外照射。发现不同辐射能量和不同脉冲数下在Bowman层和基质中的消融率与已发表的数据一致，并且可以证明首个激光脉冲存在孵育效应。
该方法无损、准确、廉价、实用，且减少了对实验动物的需求。
