Swinger C A, Wisnicki H J
Cornea. 1985;4(4):225-8.
In homoplastic keratomileusis, keratophakia, and epikeratophakia, the corneal tissue that provides the final refractive lenticule undergoes a conformational change when frozen. Because corneal tissue is composed primarily of water, an assumed value of 9.08% (approximate volumic percentage expansion of water when frozen) is frequently used for the increase in thickness, or freezing increment, rather than measuring it directly. We evaluated 32 cases of clinical keratophakia and found the increase in thickness to average 37 +/- 21%. In this series of 32 cases, the percentage of patients with a greater than 4 D residual refractive error was 16%. If an assumed freezing increment of 9.08% had been used, the percentage would have been 28%, with two-thirds of these 28% manifesting a marked undercorrection. Because of a lack of studies documenting the behavior of corneal tissue following cryoprotection and freezing, it is suggested that measurements be taken during homoplastic surgery to minimize the potential for significant inaccuracy in obtaining the desired optic result.
在同种异体角膜磨镶术、角膜镜片植入术和表层角膜镜片术中，提供最终屈光透镜的角膜组织在冷冻时会发生构象变化。由于角膜组织主要由水组成，通常使用9.08%（水冷冻时的近似体积百分比膨胀率）这一假定值来计算厚度增加量，即冷冻增量，而不是直接测量。我们评估了32例临床角膜镜片植入术病例，发现厚度增加平均为37±21%。在这32例病例中，残余屈光不正大于4D的患者比例为16%。如果使用9.08%的假定冷冻增量，该比例将为28%，其中这28%的三分之二表现为明显的矫正不足。由于缺乏记录角膜组织在冷冻保护和冷冻后行为的研究，建议在同种异体手术期间进行测量，以尽量减少在获得所需光学效果时出现重大误差的可能性。
