该文报道了一例40岁女性患者，因“双眼渐进性视物模糊3个月”就诊。患者既往于2005年因高度近视行双眼准分子激光原位角膜磨镶术 (LASIK)。最佳矫正视力OD：0.2 (–11.00 DS/ –1.25 DC×170 °)，OS：0.7 (–4.00 DS/ –0.75 DC×25 °)。双眼角膜透明，前房中深，晶状体混浊，豹纹状眼底伴后巩膜葡萄肿。诊断为双眼并发性白内障，并行右眼白内障超声乳化联合人工晶状体 (IOL) 植入术，术中植入+14.0 D IOL一枚，目标屈光度为–0.5 D。术后1周裸眼视力0.3，验光结果示右眼屈光度+2.75 DS，最佳矫正视力0.7。术后2周行右眼IOL置换术，由+14.0 D置换为+17.0 D。右眼术后1周裸眼视力0.8，验光结果示右眼屈光度–0.75 DC×15 °。

It is reported in this article that a 40-year-old female patient presented with "progressive blurred vision of both eyes for 3 months". The patient underwent bilateral laser in situ keratomileusis (LASIK) because of high myopia in 2005. It was recorded that her best corrected visual acuity was 0.2 (–11.00 DS/ –1.25 DC×170 °) in the right eye and 0.7 (–4.00 DS/ –0.75 DC×25 °) in the left, and clear cornea, normal anterior chamber, cloudy lens, tessellated fundus with posterior staphyloma in both eyes. The patient was diagnosed with bilateral complicated cataract. Phacoemulsification combined with intraocular lens (IOL, +14.0 diopter (D)) implantation was performed on the right eye, with the target –0.5D refractive diopter . One week after surgery, it was recorded that the uncorrected visual acuity of the right eye was 0.3, and the best corrected visual acuity was 0.7 (+2.75 DS). IOL replacement of the right eye was performed two weeks after surgery, the +14.0 D IOL was replaced by +17.0 D IOL. One week after surgery, the uncorrected visual acuity of the right eye was 0.8 (–0.75 DC×15 °).

Background: Corneal ectasia is a serious complication after laser in situ keratomileusis (LASIK). Ideally, patients at risk of ectasia should be identified prior to laser as unsuitable for LASIK, however, at present, there is no absolute test, system, or marker that can unequivocally identify patients at risk of developing ectasia. It has been suggested that changes in the forward protrusion of the posterior cornea or posterior corneal elevation (PCE) may be a key to the early detection of ectasia after LASIK. The purpose of this study was to examine the long term changes of the PCE after myopic LASIK using the ORBSCAN® IIz (Bausch & Lomb, Rochester, USA) and to evaluate the contributory preoperative factors to PCE changes.

Methods: This was a retrospective longitudinal case series. Forty-two eyes of 23 consecutive myopic patients who underwent uneventful LASIK surgery 6 years ago were recalled for a postoperative follow-up examination using the ORBSCAN® IIz to determine the elevation changes to the posterior corneal surface from the preoperative measurements. A forward shift of the posterior surface was given a negative value. Correlation analyses and forward stepwise regression analyses were performed to evaluate the effect of each of the preoperative parameters on the changes in PCE. Statistical and graphical analyses were performed.

Results: There was no statistical difference between the mean best-fit sphere (BFS) pre-LASIK and 6 years postop (P=0.25). Forty-two post-LASIK eyes had a mean posterior displacement of -9.38±9.84 μm (range, 12 to -31 μm) 6 years after LASIK. Forward stepwise multiple linear regression analysis indicated that the ablation spherical equivalent (ASE) was the only indicator of the forward shift of the posterior cornea after LASIK.

Conclusions: The present study identified a significant forward shift of the posterior cornea 6 years after LASIK. The ASE was the most significant prognostic determinant for forward protrusion of the posterior cornea after LASIK. 

Background: Corneal ectasia is a serious complication after laser in situ keratomileusis (LASIK). Ideally, patients at risk of ectasia should be identified prior to laser as unsuitable for LASIK, however, at present, there is no absolute test, system, or marker that can unequivocally identify patients at risk of developing ectasia. It has been suggested that changes in the forward protrusion of the posterior cornea or posterior corneal elevation (PCE) may be a key to the early detection of ectasia after LASIK. The purpose of this study was to examine the long term changes of the PCE after myopic LASIK using the ORBSCAN® IIz (Bausch & Lomb, Rochester, USA) and to evaluate the contributory preoperative factors to PCE changes.

Methods: This was a retrospective longitudinal case series. Forty-two eyes of 23 consecutive myopic patients who underwent uneventful LASIK surgery 6 years ago were recalled for a postoperative follow-up examination using the ORBSCAN® IIz to determine the elevation changes to the posterior corneal surface from the preoperative measurements. A forward shift of the posterior surface was given a negative value. Correlation analyses and forward stepwise regression analyses were performed to evaluate the effect of each of the preoperative parameters on the changes in PCE. Statistical and graphical analyses were performed.

Results: There was no statistical difference between the mean best-fit sphere (BFS) pre-LASIK and 6 years postop (P=0.25). Forty-two post-LASIK eyes had a mean posterior displacement of -9.38±9.84 μm (range, 12 to -31 μm) 6 years after LASIK. Forward stepwise multiple linear regression analysis indicated that the ablation spherical equivalent (ASE) was the only indicator of the forward shift of the posterior cornea after LASIK.

Conclusions: The present study identified a significant forward shift of the posterior cornea 6 years after LASIK. The ASE was the most significant prognostic determinant for forward protrusion of the posterior cornea after LASIK. 

目的：观察 NIDEK EC5000 准分子激光治疗系统准分子激光原位角膜磨镶术(Laser in sitkeratomileusis, LASIK) 角膜切削深度的可预测性。
方法：采用 NIDEK EC5000 准分子激光系统对 79 例近视和(或)近视散光患者进行标准 LASIK 手术，术中使用超声角膜测厚仪分别测量制瓣后和激光切削后的剩余角膜床厚度，计算实际角膜切削深度，比较实际角膜切削深度同理论预测角膜切削深度的差异。
结果：LASIK 术中实际切削深度(92.32±29.86) μm，预测切削深度(74.16±25.95) μm，两者差值(18.16 ± 14.71) μm 有统计学意义(P < 0.001)。实际切削深度与预测切削深度具有较好的相关性，相关系数为0.87 (P < 0.001)，其直线回归方程为Y = 18.06 + 1.001X。按术前角膜 K 值、术前等效球镜绝对值及术前中央角膜厚度值分组的实际切削深度与预测切削深度的差值均有统计学意义。实际切削深度与术前等效球镜有关，与术前中央角膜厚度和 K 值无关。实际切削深度与预测切削深度差值同 K 值、等效球镜，术前中央角膜厚度均无关。
结论：NIDEK EC5000 准分子激光系统 LASIK 术中实际角膜切削深度比预测角膜切削深度高 (18.16±14.71) μm，在手术设计时要考虑实际切削与机器标示值存在偏差，应尽可能多的预留剩余角膜基质床厚度，以提高手术安全性。

Purpose: To assess the predictability of corneal ablation depth in LASIK using NIDEK EC5000 excimer laser.
Method: Standard LASlK surgery was performed in 79 myopic patients with or without astigmatism with the NDEK EC5000 excimer laser system. Ultrasonic cornealpachymetry was performed immediately after flap creation and after laser ablation during LASIK procedure, by which the actual corneal ablation depth was calculated.The values of actual and predicted ablation depth were compared.
Results: The actual ablation depth was (92.32+29.86) μm, the predicted ablationdepth was (74.16+25.95) μm. The differences between them (18.16+14.71) μm were statistically significance (P < 0.001 ). Linear regression suggested that the actual ablation depth correlated closely with the predicted ablation depth (r = 0.87 , P < 0.001 ). The regression model was Y = 18.06+1.001X. The differences remained statistically significant and were independent of the levels of preoperative corneal keratometry, absolute preoperative spherical equivalent and the preoperative central cornea thickness.
Conclusion: The actual ablation depth was about (18.16+14.71) μm thicker than thepredicted ablation depth in the NlDEK EC5000 excimer laser system. We may have totake into account this deviation in order to ensure sufficient thickness of residualstromal bed.