角膜屈折矯正手術前後の角膜形状の変化  [in Japanese] Change in Corneal Curvature Before and After Corneal Refractive Corrective Surgery  [in Japanese]

スリットスキャン方式のオーブテック社製オーブスキヤン(Version 2.10)を用いて,角膜屈折矯正手術前後の角膜前後面曲のBest Fit Sphere,および角膜中央厚の測定を行い,角膜中心より半径3mmで囲まれる角膜の断面積を求めて角膜屈折率変化を比較検討した。対象は当院にてLaser in situ keratomileusis (LASIK)を施行した40例80眼。平均36.5歳。LASIK後,角膜断面積が減少することにより角膜前面BFSはフラット化するのに対し,角膜後面BFSはスティープ化する傾向が分かった。角膜前後面BFS変化量各々と角膜断面積変化量は,ばらつきが大きいが,両者の和(Y)と角膜断面積変化量(X)を比較検討すると,Y=-0.20X-0.017という関係式が得られた。又,角膜断面積変化量と実際に切除する角膜厚量とは比例関係が成立したことより,角膜切除量と角膜前後面の変化量との和に比例関係がある事が判明した。現在,LASIKをはじめとする角膜屈折矯正手術は角膜前面解析を基にして施行されているが,今回の結果,角膜後面の変化を盛り込むことにより,術後結果をより正確に予測できるのではないかと考えられた。

We used an Orbscan slit scan type, made by Orbtek Inc., to compare the relationships among the Best Fit Spheres (BFS) in anterior and posterior corneal curvatures, corneal thickness, and sectioned corneal area taken at 3-mm from the center before and after refractive corneal surgery therapy. This study consisted of 40 cases with 80 eyes in which laser in situ keratomileusis (LASIK) therapies were performed at our hospital. The average age was 36.5 years. We found that the sectioned corneal area decreased after the LASIK; and at the same time, the BFS were flatten for anterior corneal curvature, and steepen for posterior corneal curvature. Although there were no consistent relationships derived when each BFS change in the anterior and posterior corneal curvatures were separately analyzed, two combined BFS changes, as a total (Y), were found to have a relationship to the changes in the sectioned corneal area (X) in the equation of Y=-0.20X-0.017. We also found that there was a proportional relationship between the changes in the sectioned corneal area and the actual measurements of sectioned corneal thickness. Therefore, we reached the conclusion that the total changes in BFS in the anterior and posterior corneal curvatures were also proportionally related to the amount of sectioned corneal thickness. At present, refractive corneal surgeries, including LASIK, are performed based on data obtained from the analysis of only the anterior corneal curvature. However, if we include the changes in the posterior corneal curvature to the analysis, we may have a more accurate estimation of the final outcome.