准分子激光角膜切削中心的角膜地形图分析

目的探讨准分子激光角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）的切削中心对视功能的影响。方法采用Ｅｙｅｓｙｓ角膜形态分析系统对随访６个月以上的９８例（１５８只眼）ＰＲＫ前、后１０天的角膜地形图进行分析，确定激光切削中心相对入射瞳孔中心的方向、距离；比较单区和多区域激光切削的偏中心差异。结果切削区中心相对入射瞳孔中心：０～０．５ｍｍ者１００只眼（６３．３％），０．５～１．０ｍｍ者５５只眼（３４．８％），＞１．０ｍｍ者３只眼（１．９％），平均０．４５ｍｍ。多区域切削３８只眼及单区域切削１２０只眼，其偏心量分别为０．５５ｍｍ和０．４４ｍｍ。差异有显著性（ｔ检验，Ｐ＜０．０５）。偏中心切削致术后最好矫正视力下降１～２行者４只眼，其偏心量＞０．５ｍｍ。结论严重的偏心切削将影响术后视功能恢复，术中眼球跟踪系统（ｐａｓｓｉｖｅｅｙｅ－ｔｒａｃｋｉｎｇ，ＰＥＴ）的应用有利于切削中心的确定，减少偏心量。

Topographical evaluation of centration of excimer laser photorefractive keratectomy

Objective To evaluate the situation of centrality of excimer laser photorefractive keratectomy (PRK).Methods Eyesys Corneal Analysis System was used for the computer assisted analysis of corneal differential topographical maps gained preoperatively and 10 days postoperatively in 158 eyes of 98 patients with at least six months of follow up to determine the direction and the distance of the center of ablation zone relative to the center of the entrance pupil,and a comparison in decentration difference was made between one zone ablated eyes and multi zone ablated eyes.Results Concerning the centration of ablated zone relative to the center of entrance pupil:100 eyes (63 3%)were centered within 0.50mm,55 eyes (34.8%)were decentered more than 0.50mm with 3 eyes (1.9%)being decentered more than 1mm, and the mean decentration amount was 0.45mm. 38 eyes were performed by multi zone ablation and 120 eyes by one zone ablation,their mean amount of decentration was 0.55mm and 0.44 mm respectively,the difference being significant ( P <0 05). 4 eyes with decentration greater than 0.50mm lost one to two lines of their best corrected visual acuity postoperatively due to the decentered ablation.Conclusion Many factors contribute to decentration of the ablated zone.Great decentration will affect the reovery of the postoperative visual acuity. The Passive Eye Tracking System (PET) will contribute to precise centration and reduction of displacement.