Eye movement during laser in situ keratomileusis

PURPOSE: To measure eye motion in patients having laser in situ keratomileusis (LASIK) using a video technique and determine centration and variance of the eye position during surgery. SETTING: Laser refractive surgery center. METHODS: The procedure was videotaped in 5 consecutive eyes having LASIK performed by a single surgeon with the VISX Star S2 excimer laser. Following surgery, video images of the eyes were digitized and stored in a computer for processing. Digitized images were obtained at a rate of 25 images per second during the laser procedure. The pupil margin and a visual landmark, such as a scleral blood vessel, were identified in the initial image of each eye. Custom software was used to track the location of the landmark and the pupil center in subsequent images. RESULTS: Three of the 5 eyes were well centered on average. The remaining 2 eyes were decentered inferiorly by approximately 0.25 mm. The standard deviation in all eyes was approximately 0.10 mm. CONCLUSIONS: With these techniques, the position of the entrance pupil center relative to the excimer laser axis could be determined. Although the system is not fast enough to be used during surgery, it does allow quantification of centration and intraoperative motion after surgery.     

Rotational malposition during laser in situ keratomileusis

PURPOSE: To investigate the degree of rotational malposition in eyes undergoing laser in situ keratomileusis. DESIGN: Prospective observational study. METHODS: We measured the rotational position of 240 eyes of 169 patients who underwent treatment for myopic or hyperopic astigmatism with the Alcon Summit Autonomous (Orlando, Florida) LADARVision excimer laser. Immediately preoperatively, each eye was marked while the patient was seated upright. Rotational position was measured on the supine patient immediately before beginning the laser exposure. RESULTS: For all 240 eyes, mean +/- standard deviation (SD) torsional misalignment was 4.1 +/- 3.7 degrees (right eye 3.8 +/- 3.7 degrees, left eye 4.2 +/- 3.6 degrees). A total of 20 eyes (8%) had a deviation of greater than 10 degrees. CONCLUSIONS: A 4 degree and 10 degree misalignment would theoretically result in a 14% and 35% undercorrection of astigmatism, respectively. Preoperative marking of the upright patient and subsequent rotational alignment of the supine patient before laser treatment may reduce the error in correction of astigmatism during excimer laser vision correction surgery.     

Corneal interface contamination during laser in situ keratomileusis

PURPOSE: To measure the rate of corneal interface contamination during laser in situ keratomileusis (LASIK), determine probable sources of the contamination, and evaluate how the cornea reacts to the contamination. SETTING: Department of Ophthalmology, Baqyatallah Hospital, Baqyatallah University, Tehran, Iran. METHODS: In this case series, 200 eyes were evaluated for the corneal interface contamination at the end of LASIK. Cultures were taken from the upper and lower eyelid margins and the inferior fornices before surgery and from the corneal interface and the instrument at the end of surgery. Media were cultured at 37 degrees C for 14 days under aerobic and anaerobic conditions. Bacteria from positive cultures were isolated and identified by biochemical procedures to determine the species of the organisms. RESULTS: The rate of contamination was 24.5%. The most common retrieved organism was Staphylococcus epidermidis (43 cases, 87.7%). None of the contaminated or noncontaminated cases developed corneal ulcers; however, 2 eyes developed diffuse lamellar keratitis. CONCLUSION: The corneal stroma has the ability to clear introduced microorganisms during LASIK.     

Corneal perforation during laser in situ keratomileusis.

Two cases of corneal perforation that occurred during laser ablation but not during flap formation in laser in situ keratomileusis (LASIK) are reported. In the first case, no problem in flap formation occurred, and stromal bed thickness was assumed to be about 239 microns after laser application. However, a stromal bed perforation was found when 608 pulses were applied (theoretical ablation depth was 140 microns). Excessive dehydration due to prolonged exposure to the operating microscope light may change the ablation rate and cause corneal perforation. In the second case, LASIK retreatment was performed using the original flap for correction of regressed myopia (-4.0 diopters). Although the stromal bed thickness was assumed to be about 175 microns after the laser application, a stromal bed perforation was found when 151 pulses were applied (theoretical ablation depth was 37 microns). Unexpected corneal ectasia after the first LASIK treatment may cause a corneal perforation in LASIK retreatment. In conclusion, excessive dehydration of the cornea should be avoided, and careful examination of the corneal shape is necessary to prevent corneal perforation during laser ablation in LASIK.     

Corneal bed perforation by laser ablation during laser in situ keratomileusis

A 34-year-old man was referred to our department with corneal perforation after multiple laser in situ keratomileusis procedures for myopia. Corneal perforation occurred at the time of laser application during the fourth surgery, and the anterior chamber became completely flat. The perforation was sealed shortly thereafter and the corneal edema disappeared in 3 weeks, but there was an 86 microm forward shift of the cornea associated with an 8.0 diopter myopic shift during the subsequent 6 months. No further forward bulging of the cornea was observed. The refraction had stabilized up to 2 years postoperatively, but corneal irregular astigmatism limited the patient's best spectacle-corrected visual acuity.     

Flap tearing during lift-flap laser in situ keratomileusis retreatment

A flap tear occurred during laser in situ keratomileusis (LASIK) retreatment using a flap-lifting technique in 1 eye of 2 patients 4 to 5 months after the primary procedure. In the first case, the tear occurred in a decentered, standard thickness flap (168 mum) in a location close to the corneal limbus and limbal vessels. In the second case, the tear occurred in a well-centered thin flap (116 mum) that involved a peripheral corneal pannus. The false track was identified early, and central extension of the tear was averted. After the flap was successfully dissected, retreatment was performed without further complications. This report suggests that flaps with margins near the limbus or a corneal pannus may be prone to an earlier and stronger healing process at the edge that may lead to a flap tear during LASIK retreatment. This may be of increasing importance because of the trend toward larger flap diameters.     

LASIK术中眼球旋转的临床观察

目的:测量LASIK手术患者术中发生的眼球旋转。方法:选择近视患者70例140眼,术前运用AMO的WaveScan Wave FrontTM System在暗室中取坐位进行波前像差的测量,术中运用AMOVISXS4IR手术系统在卧位进行虹膜定位,测量眼球的旋转度数,所有患者均采用波前引导的LASIK手术。结果:发生顺时针旋转73眼,发生逆时针旋转47眼。旋转<3°者74眼,3°<旋转<5°者30眼,5°<旋转<7°者12眼,旋转>7°者4眼。其余20眼虹膜定位不成功。结论:LASIK手术中由于患者的紧张和体位的改变会导致眼球的旋转,AMO的WaveScan WaveFrontTM System和AMO VISX S4 IR手术系统能够有效测量眼球旋转,更好的矫正散光。     

LASIK手术中眼球旋转的观察研究

目的:探讨LASIK手术中患者发生眼球旋转的特点和规律.方法:对203例(394眼)患者术前应用VISX波前像差仪进行虹膜照相检查,LASIK手术中利用VISX S4-IR系统进行虹膜定位检查,观察手术时与检查时的眼球旋转方向和角度.结果:虹膜定位的捕捉成功率为92.6%,394眼中共有346眼在术中发生了旋转.双眼均主要为外旋,其中,右眼中,36.5%发生了内旋、63.5%发生了外旋;左眼中,36.3%的发生了内旋、63.7%发生了外旋.右眼眼球旋转的最小角度为0.1°,最大角度为8.9°;左眼眼球旋转的最小角度为0.1°,最大角度为9.6°.平均眼球的旋转角度为(2.78±2.10)°.旋转大于5°的眼球为18.5%.结论:LASIK手术时,随着从坐位到仰卧位的改变,患者普遍存在着低中度的眼球旋转问题.该问题会对患者的术后效果产生一定的影响.精确地进行虹膜定位,将有助于提高散光和高阶像差患者的手术效果.     

Hansatome零压力角膜板层刀切瓣厚度的预测性研究

目的评价Hansatome零压力角膜板层刀切出角膜瓣厚度的预测性,探讨不同因素对其的影响。方法对行LASIK者326例652眼应用超声角膜测厚仪分别于手术前后测量角膜瓣厚度,计算实际角膜瓣厚度,并对相关影响因素进行分析。结果Z160刀头第1刀角膜瓣厚度为(113.50±15.62)μm,第2刀为(104.75±13.76)μm,第2刀切瓣厚度较第1刀薄(P<0.05)。Z180刀头第1刀角膜瓣厚度为(123.24±14.35)μm,第2刀为(116.58±16.34)μm,较标示厚度薄(P<0.05)。Z160刀头配合使用8.5mm和9.5mm负压环切瓣厚度分别为(108.32±12.64)μm和(110.20±14.39)μm,Z180刀头配合使用两种负压环切瓣厚度分别为(119.50±14.52)μm和(120.34±16.38)μm,统计学处理均无显著差异。结论Hansatome零压力板层角膜刀切出角膜瓣厚度较标示厚度薄,负压环的大小与角膜瓣厚度无关。     

Corneal hydration affects ablation during laser in situ keratomileusis surgery

BACKGROUND: Studies in animal eyes indicate that the level of corneal hydration affects the ablation rate of laser surgery; the greater the hydration is, the less the ablation for a given laser pulse. Our study is an assessment in human eyes comparing the effects on ablation by blotting the corneal stromal surface under a corneal flap created for laser in situ keratomileusis (LASIK) procedures between sets of excimer laser pulses, with ablation depth in eyes not blotted between sets of laser pulses. METHODS: We modified the surgical technique for LASIK procedures to assess the effects of the level of hydration on excimer laser ablation depth per pulse. In group 1, 40 eyes underwent LASIK surgery without any modification. Group 2 was composed of 36 eyes having LASIK procedures, but the corneal surfaces were kept relatively dry by blotting of the stromal surface between sets of laser pulses. RESULTS: Six months after surgery, the mean spherical equivalent refractive change was from -8.38 diopters (D) to -1.44 D in group 1 and from -7.93 D to -0.09 D in group 2. For predictability, the deviation from the target refraction after surgery was assessed. Thirty-three percent (13 of 40) in group 1 and 25% (9 of 36) in group 2 were within +/-0.5 D. Forty-eight percent (19 of 40) in group 1 and 50% (18 of 36) in group 2 were within +/-1 D. Six months after surgery, 80% or more in both groups were within +/-2 D. There was myopic regression in all patients. Three months after surgery, regression averaged -0.71 D in group 1 and -1.15 D in group 2. CONCLUSIONS: Corneal hydration levels affect the efficiency of laser ablation in LASIK procedures. With less hydrated corneas, ablation effects were greater than for corneas not blotted during the procedure, but these patients appear to undergo greater myopic regression.     

Visual performance after interface haemorrhage during laser in situ keratomileusis

AIM: To study the visual performance in eyes with interface haemorrhage during laser assisted in situ keratomileusis (LASIK). METHODS: Case records of 20 patients, who had bleeding from the limbal vessels in one eye during LASIK (group 1) and uncomplicated surgery in the fellow eye (group 2) were studied. The parameters evaluated were uncorrected visual acuity (UCVA) best corrected visual acuity (BCVA), spherical equivalent of refraction (SEQ), contrast sensitivity, and glare acuity preoperatively and at 1, 3, and 6 months postoperatively. RESULTS: The mean preoperative SEQ in group 1 and 2 eyes was -5.79 (2.3) D and -5.27 (1.68) D, respectively. The mean decimal UCVA at 6 months after LASIK in group 1 and 2 eyes were 0.6 (0.2) and 1.0 respectively (p<0.001). The mean decimal BCVA at 1 week after LASIK in group 1 and 2 eyes were 0.89 (0.04) and 1.0 respectively (p<0.05). However, all eyes had a BCVA of 6/6 at 1, 3, and 6 months after LASIK. The mean contrast sensitivity values preoperatively in group 1 and 2 eyes were 161.3 (8.7) and 172 (68.2) respectively. There was a significant decrease in group 1 at 6 months (102 (60.5) (p<0.01)) compared to group 2. The decimal glare acuity preoperatively in group 1 and 2 eyes was 0.95 (0.11) and 0.89 (0.12), respectively. It decreased significantly in group 1 (0.7) (0.1 (p<0.01)) compared to group 2 at the 6 month follow up. CONCLUSION: Occurrence of intraoperative interface haemorrhage may affect the visual performance following LASIK surgery.     

LASEK治疗LASIK术后屈光欠矫

目的 :探讨准分子激光上皮下角膜磨镶术 (LASEK)治疗准分子激光原位角膜磨镶术 (LASIK)术后屈光欠矫的疗效。方法 :对LASIK术后屈光欠矫的 11例 (2 0只眼 )施行LASEK。结果 :术后 6个月视力和屈光度趋于稳定 ,术后 3个月角膜Haze 0级者 15只眼 ,0 5级者 4只眼 ,1级者 1只眼。术后 6个月 ,裸眼视力≥ 0 6、≥ 1 0者分别为 2 0只眼 (10 0 % )、14只眼 (70 % )。屈光度≤± 1 0 0D者为 19只眼 (95 % )。结论 :LASEK治疗LASIK术后屈光欠矫安全 ,有效。     

准分子激光原位角膜磨镶术的并发症

准分子激光原位角膜磨镶术是目前最常见的一种角膜屈光手术,但是它仍然存在并发症,如角膜瓣相关并发症、准分子激光消融的并发症、弥漫性角膜炎、感染性角膜炎、角膜瓣下上皮植入、干眼、医源性圆锥角膜及视网膜病变等,只有尽早作出诊断并进行相关处理,才能提高手术成功率.     

准分子激光原位角膜磨镶术适应证的选择

准分子激光原位角膜磨镶术是目前临床最常用的角膜屈光手术.术前应当严格把握适应证,特别是对角膜厚度薄、瞳孔大、顿挫型圆锥角膜或其他角膜扩张、自身免疫性疾病、单纯疱疹病毒角膜炎、青光眼、角膜的生物力学异常以及角膜屈光术后、白内障术后和穿透性角膜移植术后残留屈光不正等一些特殊患者的手术方式选择及相应处理,才能更好地提高手术成功率,并减少术后并发症.     

二次LASIK手术治疗近视欠矫

评价再次ＬＡＳＩＫ矫正残余近视的效果,可预测性、安全性。方法对４０只眼ＬＡＳＩＫ术后屈光欠矫的患者行二次手术,两次手术间隔时间３－２４个月。分别在二次术后３天、１、３和６个月随访观察。结果术后各随访时间患眼平均裸眼视力较术前明显提高,最佳矫正视力与术前无显著差异,术后后平均屈光度较术前减,差异有显著性,切削直径适量增大可减术后屈光回退;结论二次ＬＡＳＩＫ手术是必要、安全、可行的。     

Ectasia after laser in situ keratomileusis

PURPOSE OF REVIEW: The potential for litigation has resulted in increased interest in ectasia after laser in situ keratomileusis. This article summarizes papers written during this past year on this subject. RECENT FINDINGS: A panel of refractive surgery experts have summarized the current state of knowledge on this subject and provided guidelines to minimize risk. Because ectasia may occur in the absence of risk factors, there may be corneas with biomechanical factors not detectable with present technology which are at risk. Several articles point out the limitations of the Orbscan (Bausch & Lomb, Rochester, New York, USA), in particular its accuracy and reproducibility with regard to data generated from the posterior surface of the cornea. A biomechanical model of the cornea is proposed which suggests that each cornea's response to laser in situ keratomileusis is unique. Several case reports are also reviewed which provide insight into pathogenesis and potential new treatment options; these include reports on histopathology, topographic pseudokeratectasia, ectasia from transient raised intraocular pressure, poor response to laser in situ keratomileusis after incisional surgery, intracorneal rings, collagen cross-linking and conductive keratoplasty to stabilize and sphericize the cornea with ectasia. SUMMARY: Our knowledge about ectasia is still in evolution. Insights into the biomechanics and genetics of the cornea may allow us to further reduce its occurrence.     

准分子激光原位角膜磨镶术适应证的选择

准分子激光原位角膜磨镶术是目前临床最常用的角膜屈光手术.术前应当严格把握适应证,特别是对角膜厚度薄、瞳孔大、顿挫型圆锥角膜或其他角膜扩张、自身免疫性疾病、单纯疱疹病毒角膜炎、青光眼、角膜的生物力学异常以及角膜屈光术后、白内障术后和穿透性角膜移植术后残留屈光不正等一些特殊患者的手术方式选择及相应处理,才能更好地提高手术成功率,并减少术后并发症.