Ablation centration in laser in situ keratomileusis for hyperopia: comparison of VISX S3 ActiveTrak and VISX S2

PURPOSE: To compare ablation centration and outcome measurements in laser in situ keratomileusis (LASIK) for hyperopia using the pupil-tracking VISX S3 ActiveTrak or the nontracking VISX S2 excimer laser. METHODS: In a retrospective study, 49 consecutively treated hyperopic eyes (32 patients) that had LASIK by the VISX StarS3 ActiveTrak were compared to 49 control-matched eyes treated with the VISX StarS2 without pupil-tracking. Primary outcome variables including ablation centration, uncorrected visual acuity, best spectacle-corrected visual acuity, manifest refraction, complications, and induced cylinder analyzed by vector analysis were evaluated 3 months postoperatively. RESULTS: Hyperopic sphere ranged between plano and +5.50 D and cylinder between 0 and +2.75 D. Ninety-five of 98 eyes (96.9%) were available for analysis at 3 months. Of these 95, 52 eyes could be used for analysis of ablation centration. Mean decentration of the ablation zone from the entrance pupil was 0.30 +/- 0.20 mm in tracked eyes (n=31) and 0.41 +/- 0.39 mm in nontracked eyes (n=21), P=.17. Two eyes (6.5%) in the tracked group were significantly decentered between 0.5 and 1 mm from the pupil center. In the nontracked group, decentration was between 0.5 and 1 mm in one eye (4.8%) and greater than 1 mm in two eyes (9.5%). CONCLUSIONS: Comparable ablation centration in LASIK for hyperopia was achieved between actively-tracked and nontracked eyes. Decentrations (greater than 1 mm) were not seen with a tracking system in this study. Visual and refractive results were similar between the VISX StarS3 ActiveTrak and VISX StarS2 laser systems.     

Topographic centration of ablation after LASIK for myopia using the CustomVue VISX S4 excimer laser

PURPOSE: To determine the ablation centration, efficacy, predictability, and safety of CustomVue LASIK using the VISX S4 excimer laser for the treatment of myopia and myopic astigmatism. METHODS: A retrospective review of 20 myopic eyes of 12 patients treated with LASIK CustomVue VISX S4 was conducted. Corneal topography was used to determine ablation centration. Primary outcome variables including manifest refraction, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), and complications were evaluated at 3 months postoperatively. RESULTS: Mean decentration (from ablation zone to entrance pupil) was 0.23 +/- 0.08 mm at 3 months postoperatively. No eyes were decentered > 0.5 mm. Preoperatively, the mean spherical equivalent refraction was -4.81 +/- 11.39 diopters (D) (range: -6.75 to -2.25 D). At 3 months postoperatively, mean spherical equivalent refraction was -0.63 +/- 0.25 D (range: -2.00 to 0.25 D). Nineteen (95%) of 20 eyes had UCVA of 20/40 and 16 (80%) of 20 eyes had UCVA of 20/20 at 3 months postoperatively. Fourteen (70%) eyes were within +/- 0.50 D and 18 (90%) eyes were within +/- 1.00 D of emmetropia. No eye lost > 1 line of BSCVA. CONCLUSIONS: Wavefront-guided LASIK using the CustomVue VISX S4 for myopic eyes results in minimal decentration ablation and effective, predictable, and safe visual outcomes.     

CustomVue laser in situ keratomileusis for myopia and myopic astigmatism using the Visx S4 excimer laser: Efficacy, predictability, and safety

PURPOSE: To evaluate the efficacy, predictability, and safety of custom laser in situ keratomileusis (LASIK) using the Visx wavefront platform CustomVue for the treatment of myopia and myopic astigmatism. SETTING: Stanford University Eye Laser Center, Stanford, California, USA. METHODS: This retrospective analysis was of the initial 140 eyes of 78 patients treated consecutively with LASIK for myopia using the Visx Star S4 excimer laser. Primary outcome variables, including uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and complications, were evaluated at 1 week and 1 and 3 months. Vector analysis was performed on eyes that received astigmatic correction. RESULTS: Mean preoperative spherical equivalent (SE) was reduced from -3.89 diopters +/- 1.48 (SD) to an SE of -0.21 +/- 0.36 D at 1 month and -0.28 +/- 0.36 D at 3 months (P < .001). At 1 and 3 months, UCVA was 20/20 or better in 84.3% and 87.9%, respectively. Eighty-six percent of eyes at 1 month and 81.4% of eyes at 3 months were within +/-0.5 D of emmetropia. No eyes lost more than 2 lines of BSCVA. Vector analysis yielded an index of success of 0.39, indicating a 61% success rate in achieving the astigmatic surgical correction at 3 months. The preoperative root-mean-square value of 0.28 +/- 0.08 microm increased slightly to 0.33 +/- 0.11 microm at 1 month and 0.34 +/- 0.11 microm at 3 months. CONCLUSION: Wavefront-guided LASIK using the Visx CustomVue system was effective, predictable, and safe for correction of low to moderate myopic refractive error.     

Comparison of LADARVision and Visx Star S3 laser in situ keratomileusis outcomes in myopia and hyperopia

PURPOSE: To compare visual outcomes with 2 commonly used excimer lasers, the Autonomous LADARVision (LV) (Alcon Laboratories Inc.) and the Visx Star S3 (S3), in the performance of myopic and hyperopic astigmatic laser in situ keratomileusis (LASIK). SETTING: Zale Lipshy University Hospital Laser Center for Vision, University of Texas Southwestern Medical Center, Dallas, Texas, USA. METHODS: In this retrospective single-center 3-surgeon cohort comparison, 100 consecutive LV-treated myopic eyes with a mean manifest refraction spherical equivalent (MRSE) of -3.22 diopters (D) (range 0 to -6.00 D) (mean astigmatism 0.95 D [range 0 to 4.00 D]) were compared with 100 consecutive S3-treated eyes with a similar MRSE (mean MRSE -3.19 D; mean astigmatism 0.66 D [range 0 to 2.75 D]). Forty-one consecutive LV-treated hyperopic eyes with a mean MRSE of +2.59 D (range +1.00 to +6.00 D) (mean astigmatism 0.89 D [range 0 to 3.50 D]) were compared with 25 consecutive S3-treated eyes with a similar MRSE (mean MRSE +2.70 D; mean astigmatism 0.87 D [range 0 to 2.75 D]). The following outcomes were compared: uncorrected visual acuity, refractive predictability and stability, gain or loss of best spectacle-corrected visual acuity, and need for enhancement. RESULTS: Statistically significant differences in outcomes were found between lasers in the treatment of hyperopia and hyperopic astigmatism. No outcome differences between lasers were found in the treatment of myopia and myopic astigmatism. CONCLUSION: The LV and S3 lasers yielded equivalent results in myopic LASIK between 0 and -6.00 D; however, the LADARVision yielded statistically significantly better results in hyperopic LASIK between +1.00 and +6.00 D.     

Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis

PURPOSE: To evaluate the size, shape, and uniformity of the videokeratographic functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) in 2 cohorts of patients with equivalent amounts of preoperative myopic or hyperopic astigmatism. SETTING: Pepose Vision Institute, St. Louis, Missouri, USA. METHODS: Eyes with myopic or hyperopic astigmatism (n=27 in each group) that had LASIK with the Visx Star S3 laser were retrospectively selected to match for level of preoperative refractive error. Slit-scanning videokeratography was performed preoperatively and 6 months postoperatively and analyzed using custom software. The FOZ was calculated by analyzing refractive power maps using a region-growing algorithm. Difference maps were generated from slit images and compared for interval change in corneal elevation, tangential curvature, and refractive power. The difference maps were also averaged (mean difference maps) for each target population. A Zernike decomposition of corneal first-surface elevation was performed to compare postoperative values with baseline parameters. RESULTS: The mean postoperative refractive sphere at 6 months was -0.17 diopter (D) +/- 0.66 (SD) and +0.25 +/- 0.85 D in the myopia group and hyperopia group, respectively, and the mean postoperative astigmatism, -0.49 +/- 0.32 D and -0.65 +/- 0.52 D, respectively (P=.11). Based on the refractive power maps, the mean preoperative and postoperative myopic FOZ was 33.09 +/- 7.30 mm(2) and 30.94 +/- 5.43 mm(2), respectively, and the mean hyperopic FOZ, 33.19 +/- 7.96 mm(2) and 37.99 +/- 6.88 mm(2), respectively. After LASIK, there was an increase in magnitude of negative anterior corneal surface spherical-like Zernike values in the myopia group (P<.0001) and an increase in magnitude of positive spherical-like Zernike values in the hyperopia group. Postoperatively, significant induction of corneal surface horizontal coma was noted in hyperopic eyes (P<.0001). Hyperopic eyes, on average, had larger topographic FOZs after LASIK, but with less uniformity of curvature and power change than myopic eyes. CONCLUSIONS: Hyperopic LASIK, which involves more transition points along the ablation diameter, produced a less uniform topographic FOZ than typical myopic treatments. Less predictable biomechanical changes from the circumferential release of tension on collagen bundles after midperipheral hyperopic ablation and greater variation in beam centration and the angle of incidence may contribute to the greater variability in corneal curvature and power in hyperopic LASIK than in myopic LASIK.     

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.     

Centration analysis of ablation over the coaxial corneal light reflex for hyperopic LASIK

PURPOSE: To analyze postoperative topographic centration when the coaxially sighted corneal light reflex was used for laser centration in hyperopic LASIK. METHODS: Centration photographs of 21 eyes (12 patients) that underwent hyperopic LASIK with centration over the coaxially sighted corneal light reflex were reviewed to determine the distance from the entrance pupil center to the coaxially sighted corneal light reflex. Postoperative ablation centration was determined topographically at day 1 and 3 months by four different methods. The difference between the actual decentration and the decentration that would have occurred had the ablation been centered over the entrance pupil center was calculated. RESULTS: The mean deviation of the coaxially sighted corneal light reflex from the entrance pupil center preoperatively was 0.34 +/- 0.24 mm nasal or 4.5 +/- 3.0 degrees. At 1 day, the average decentration was 0.10 mm or 1.3 degrees temporal. The mean decentration that would have occurred if the ablation had been centered over the entrance pupil center was 0.44 mm or 5.5 degrees temporal. At 3 months, the average decentration was 0.07 mm or 0.25 degrees temporal. The mean decentration that would have occurred if the ablation had been centered over the entrance pupil center was 0.45 mm or 5.6 degrees temporal. Mean uncorrected visual acuity (logMAR) improved 3 lines from 0.54 +/- 0.14 (20/70) to 0.22 +/- 0.17 (20/32). No eye lost >2 lines of best spectacle-corrected visual acuity (BSCVA); 2 (10%) eyes lost 1 line of BSCVA at 3-month follow-up. CONCLUSIONS: Excellent centration in hyperopic ablation is possible even in eyes with positive angle kappa when the ablation is centered over the corneal light reflex.     

Treatment of previous decentered excimer laser ablation with combined myopic and hyperopic ablations

PURPOSE: Decentration of the ablation zone is an occasional complication of excimer laser refractive surgery. We describe a technique to recenter the ablation zone without changing the refractive status obtained by the first surgery. METHODS: Sixteen eyes of 14 patients had moderate or marked ablation decentration after previous excimer laser surgery for myopia, but with only minor residual refractive error. Five eyes had spectacle-corrected visual acuity loss and all these patients reported various symptoms such as halos, ghost images, or night driving difficulties. To recenter the ablation zone without changing the refraction, a combination myopic and hyperopic treatment was used. The hyperopic treatment was decentered toward the initial decentered myopic ablation. A myopia ablation of near equal dioptric value was then added, but decentered in the opposite direction. The Bausch & Lomb Technolas Keracor 217 laser was used. RESULTS: After the first retreatment, the centration of the ablation zone was improved in 15 of the 16 eyes. All eyes with initial spectacle-corrected visual acuity loss recovered lines of visual acuity. Subjective decrease of symptoms was described as follows: nil in one eye, mild in one eye, moderate in four eyes, and marked in ten eyes. A second retreatment was needed in five eyes: in two to improve centration and in three to correct residual ametropia. The only complication (one eye) was induced decentration 180 degrees away from the initial decentration with a 1-line spectacle-corrected visual acuity loss, and additional retreatment was required. CONCLUSION: A combination of decentered myopic and hyperopic ablation of an equivalent dioptric magnitude, each decentered 180 degrees apart, was a useful method to correct previous excimer laser treatment decentration, with minimal alteration of refractive status that was obtained by the initial surgery.     

Anterior corneal optical aberrations induced by laser in situ keratomileusis for hyperopia

PURPOSE: To evaluate the effects of hyperopic laser in situ keratomileusis (LASIK) on anterior corneal higher-order aberrations (HOAs) (3rd to 6th orders). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: In a retrospective study, 3rd-order to 6th-order HOAs from preoperative and 3-month postoperative corneal topographic maps of eyes that had hyperopic LASIK using the Visx Star S2 and Visx Star S3 laser systems were calculated. There were 20 eyes of 14 patients in each group; the optical and transition zones were 6.0 mm and 9.0 mm, respectively. The surgically induced changes in anterior corneal HOAs and the differences between the HOA changes in corneas treated with and without active eye tracking were analyzed. RESULTS: In both groups, hyperopic LASIK induced a significant reduction in 4th-order spherical aberration (SA) coefficients (Z4(0)) in the 3.0 mm and the 6.0 mm central zones, and the decrease was significantly correlated with increasing hyperopic correction (except in the Visx S3 group's central 3.0 mm zone). In the 6.0 mm zone in both groups, the root-mean-square (RMS) of the SA (Z4(0) and Z6(0)) decreased significantly, whereas there were no significant changes in the total HOAs. By excluding Z4(0), the mean RMS values for the remaining 21 Zernike terms increased by more than 30% (both P<.016). A simulated increase in pupil size from 3.0 to 6.0 mm caused a significantly smaller increase in SA in postoperative corneas compared to the preoperative values. Differences between the S2 and S3 groups were minimal. CONCLUSIONS: Hyperopic LASIK decreased SAs and reduced the magnitude of the SA increase that occurred with pupil dilation. Higher-order aberrations excluding the 4th-order SA increased significantly.     

Comparison of ablation centration in initial and retreatment active eye-tracker-assisted laser in situ keratomileusis and the effect on visual outcome

PURPOSE: To evaluate the relationship between initial and retreatment ablation centers in active eye-tracker-assisted myopic laser in situ keratomileusis (LASIK) and determine whether the relationship between the 2 ablation centers influences the visual outcome after retreatment. SETTING: Department of Ophthalmology, China Medical University Hospital, Taichung, Taiwan. METHODS: This retrospective study comprised 21 eyes of 15 patients who had retreatment at least 3 months after primary myopic LASIK by lifting the initial flap. Corneal topography and best corrected visual acuity (BCVA) were evaluated preoperatively and 3 months postoperatively. The ablation centration was analyzed by corneal topography preoperatively and at 3 months. RESULTS: The mean decentration of the primary treatment was 0.43 mm +/- 0.21 (SD) and of the retreatment, 0.34 +/- 0.15 mm. There was no significant difference between them (P =.07). The 2 ablation centers were close each other. The mean distance between the 2 ablation centers was 0.29 +/- 0.18 mm and the mean angle between them, 39.7 +/- 46.2 degrees. The BCVA was unchanged after retreatment regardless of the relationship between the 2 ablation centers. CONCLUSIONS: With an active eye-tracking system, the retreatment center was not only close to the pupil center but also close to the primary ablation center. Regardless of the relationship between the 2 ablation centers, the BCVA did not change if the retreatment ablation was well centered.     

Wavefront-guided laser in situ keratomileusis using the WaveScan system for correction of low to moderate myopia with astigmatism: 6-month results in 277 eyes

PURPOSE: To assess the safety and effectiveness of wavefront guided LASIK surgery using the Visx WaveScan system for correction of low to moderate myopia with astigmatism. SETTING: Multicenter study at 6 sites in the United States. METHODS: In this prospective nonrandomized clinical trial, treatments were performed at 6 sites in the United States using the WaveScan (CustomVue) guided excimer laser. A total of 351 eyes were enrolled, and 277 eyes were analyzed at 6 months. RESULTS: At 6 months, 94% of eyes achieved an uncorrected visual acuity (UCVA) of 20/20 or better and 74% achieved a UCVA of 20/16 or better. Sixty-nine percent of eyes had the same or better postoperative UCVA than their preoperative best spectacle-corrected visual acuity (BSCVA). Ninety percent of eyes were within +/-0.5 diopter of intended correction. No eye lost more than 1 line of BSCVA. Total higher-order root-mean square (RMS), coma, and spherical aberration values were stable (P<.05). CONCLUSION: The data support the safety and effectiveness of the WaveScan-guided customized laser ablation using the Visx Star S4 system for correction of low to moderate myopia with astigmatism.     

Zernike versus Fourier treatment tables for myopic patients having CustomVue wavefront laser in situ keratomileusis with the S4 excimer laser

PURPOSE: To compare the efficacy, predictability, and safety of Zernike-based versus Fourier-based treatment tables in myopic eyes 1 year after CustomVue wavefront laser in situ keratomileusis (LASIK) using the S4 excimer laser (Visx). SETTING: Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA. METHODS: A prospective analysis of 32 eyes of 16 patients with myopia who had CustomVue LASIK with the S4 excimer laser was conducted using Zernike or Fourier treatment tables. Mean spherical equivalent (SE), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and higher wavefront analyses were determined. RESULTS: The mean postoperative SE was -0.27 diopter (D) +/- 0.41 (SD) in Zernike-treated eyes and -0.20 +/- 0.29 D in Fourier-treated eyes. Twenty-eight of 32 eyes were available for analysis. Ninety-two percent of eyes in the Zernike group and all eyes in the Fourier group had 20/20 or better acuity (P = .85). Seventy-nine percent and 92%, respectively, were within +/-0.50 D of emmetropia (P = .68). All eyes in the Zernike group and 93% of eyes in the Fourier group had no change or gained at least 1 Snellen line of BSCVA (P = .85). Mean higher-order aberration values (mum) in the Zernike group and Fourier group were as follows: total root mean square, 0.91 and 0.99, (P = 0.95); defocus, 0.71 and 0.74, (P = 0.98); astigmatism, 0.15 and 0.31, (P = 0.81); coma, 0.21 and 0.20, (P = 0.99); trefoil, 0.11 and 0.11, (P = 1); and spherical aberration, 0.17 and 0.30, (P = 0.85), respectively. CONCLUSIONS: Myopic eyes that had CustomVue LASIK had better visual outcomes in the Fourier group than in the Zernike group. Higher-order wavefront aberration results were similar between the 2 groups.     

Ablation centration after active eye tracker-assisted LASIK and comparison of flying-spot and broad-beam laser

PURPOSE: To evaluate ablation centration of flying-spot LASIK, investigate the effect of patient- and surgeon-related factors on centration, and compare flying-spot and broad-beam laser results. METHODS: This retrospective study comprised 173 eyes of 94 patients who underwent LASIK with the Alcon LADARVision4000 with an active eye-tracking system. The effective tracking rate of the system is 100 Hz. The amount of decentration was analyzed by corneal topography. Patient- (low, high, and extreme myopia; effect of learning) and surgeon-related (learning curve) factors influencing centration were identified. Centration was compared to the SCHWIND Multiscan broad-beam laser with a 50-Hz tracker from a previous study. RESULTS: Mean decentration was 0.36+/-0.18 mm (range: 0 to 0.9 mm). Centration did not differ in low, high, and extreme myopia or in patients' first and second eyes. There were no significant differences in centration between the first 50 LASIK procedures and the last 50 procedures. Comparing flying-spot and broad-beam laser results, there were no differences in centration in low myopia. However, the LADARVision4000 yielded better centration results in high and extreme myopia. CONCLUSIONS: The Alcon LADARVision4000 active eye tracking system provides good centration for all levels of myopic correction and better centration than the Schwind broad-beam Multiscan in eyes with high and extreme myopia.     

LASIK手术偏心切削病例的分析

目的 分析因传统准分子激光原位角膜磨镶术（LASIK）和波前像差引导的LASIK（波前引导LASIK）偏心切削引发视觉质量下降的病例中,其高阶像差分布特征和偏心切削程度的评价.方法 回顾性病例对照研究.初次LASIK术后（包括传统LASIK和波前引导LASIK）出现重影和星芒等视觉症状的患者40例（48眼）,术后复诊3个月以上[复诊期限：波前引导组平均为9个月（4至26个月）,传统组平均为24个月（5个月至6年）],屈光度稳定在±1.00 D以内者,除外过矫、欠矫和眼表及眼内疾患导致的视力下降,行WaveScan（3.62版）波前像差仪检查.本研究选取了这部分患者中初次LASIK术后主导像差为彗差（垂直彗差或水平彗差）的26例（28眼）,分析检测所得高阶像差结果,并测定术中偏心的切削中心相对瞳孔中心在水平方向（X轴）、垂直方向（Y轴）和矢量的偏移.将波前像差引导LASIK组的术前与术后结果采用配对t检验或者配对秩和检验进行比较;波前像差引导LASIK组术后与传统LASIK组术后结果采用独立样本t检验或者独立样本秩和检验进行比较.结果 波前引导组的总高阶像差均方根值（RMS）由（0.425±0.192）μm增加至术后的（1.262±0.590）μm,增加了1.96倍.总彗差RMS值由（0.190±0.114）μm增加至术后的（0.686±0.315）μm,增加了 2.61倍.水平彗差RMS值由（0.118±0.061）μm增加至术后的（0.257±0.237）μm,增加了1.17倍;垂直彗差RMS值由（0.130±0.122）μm增加至术后的（0.587±0.329）μm,增加了3.51倍.初次LASIK术后的水平彗差明显小于垂直彗差（Z=-2.803,P=0.004）.传统组的总高阶像差、总慧差与波前引导组比较,差异无统计学意义,但总慧差占总高阶像差的比例,两组差异有统计学意义（t=-1.548,P=0.007）.偏心切削量水平方向（X轴）位移右眼为（0.65±0.38）mm,左眼为（0.90±0.35）mm;垂直方向（Y轴）位移右眼为（0.80±0.30）mm,左眼为（0.53±0.34）mm;矢量位移右眼为（1.11±0.25）mm,左眼为（1.13±0.22）mm.全部28眼矢量位移均＞0.5 mm,71%的患眼切削中心偏移瞳孔中心的距离＞1.0 mm,矢量位移程度是LASIK术后无视觉症状人群的2.02倍.右眼在垂直方向（Y轴）的位移大于左眼（t=2.157,P=0.040）结论由于偏心切削引发的LASIK术后视觉质量下降病例中,高阶像差和总彗差明显增加,垂直彗差增加大于水平彗差;其偏心切削的程度属于中度和重度偏移.因此,偏心切削是LASIK术后视觉质量下降的主要原因之一.     

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。     

Comparison of ablation centration after bilateral sequential versus simultaneous LASIK

PURPOSE: To compare ablation centration after bilateral sequential and simultaneous myopic LASIK. METHODS: A retrospective randomized case series was performed of 670 eyes of 335 consecutive patients who had undergone either bilateral sequential (group 1) or simultaneous (group 2) myopic LASIK between July 2000 and July 2001 at the China Medical University Hospital, Taichung, Taiwan. The ablation centrations of the first and second eyes in the two groups were compared 3 months postoperatively. RESULTS: Of 670 eyes, 274 eyes (137 patients) comprised the sequential group and 396 eyes (198 patients) comprised the simultaneous group. Three months post-operatively, 220 eyes of 110 patients (80%) in the sequential group and 236 eyes of 118 patients (60%) in the simultaneous group provided topographic data for centration analysis. For the first eyes, mean decentration was 0.39 +/- 0.26 mm in the sequential group and 0.41 +/- 0.19 mm in the simultaneous group (P = .30). For the second eyes, mean decentration was 0.28 +/- 0.23 mm in the sequential group and 0.30 +/- 0.21 mm in the simultaneous group (P = .36). Decentration in the second eyes significantly improved in both groups (group 1, P = .02; group 2, P < .01). The mean distance between the first and second eyes was 0.31 +/- 0.25 mm in the sequential group and 0.32 +/- 0.18 mm in the simultaneous group (P = .33). The difference of ablation center angles between the first and second eyes was 43.2 < or = 48.3 degrees in the sequential group and 45.1 +/- 50.8 degrees in the simultaneous group (P = .42). CONCLUSIONS: Simultaneous bilateral LASIK is comparable to sequential surgery in ablation centration.     

Laser in situ keratomileusis for the correction of residual ametropia after penetrating keratoplasty

PURPOSE: To evaluate the safety, efficacy, and predictability of excimer laser in situ keratomileusis (LASIK) to correct residual myopia and astigmatism after penetrating keratoplasty (PKP). SETTING: Buzard Eye Institute, Las Vegas, Nevada, USA. METHODS: Twenty-six eyes had LASIK at least 1 year after PKP. All eyes were followed for at least 6 months after LASIK; 22 eyes were followed for 12 months. Sutures were removed at a mean of 13 months post PKP. Laser in situ keratomileusis was performed with the Chiron Automated Corneal Shaper microkeratome (Bausch & Lomb) and the Visx Star excimer laser. Before LASIK, the mean spherical equivalent (SE) was -4.94 diopters (D) +/- 2.79 (SD) and the mean astigmatism was 2.71 +/- 2.33 D; all eyes had regular astigmatism or slightly decentered, irregular astigmatism. RESULTS: At the last follow-up, the mean postoperative uncorrected visual acuity (UCVA) was 20/30, the mean SE was -0.35 +/- 0.65 D, and the mean residual astigmatism was 1.06 +/- 0.67 D. Eighty-six percent of patients had an SE within +/-1.00 D of emmetropia and a UCVA of 20/40 or better. Ten eyes (39%) had 1 or more enhancements, which were performed a mean of 6 months after the primary LASIK. Significant complications such as wound dehiscence, epithelial ingrowth, and corneal decompensation did not occur. At the last follow-up, 18% of patients lost 1 line of best corrected visual acuity and 27% gained 1 line. CONCLUSION: Laser in situ keratomileusis appeared to be a reliable and safe procedure to correct residual myopia and astigmatism after PKP.     

Size of corneal topographic effective optical zone: comparison of standard and customized myopic laser in situ keratomileusis

PURPOSE: To investigate the corneal topographic effective optical zone (EOZ) in eyes after wavefront-guided myopic laser in situ keratomileusis (LASIK) and to compare them with the EOZ after standard LASIK. DESIGN: Retrospective, case-control study. METHODS: We evaluated the corneal topographic maps of 41 eyes of 25 consecutive patients who had CustomVue LASIK (CV LASIK) and 41 eyes of 23 patients who had standard LASIK with correction up to -7 diopters using the VISX Star S4 laser (VISX Inc, Santa Clara, California, USA). On the refractive map of the Humphrey Topography System, we defined the EOZ as the area outlined by a change of corneal power of 0.5 diopters from the power at the center of the pupil. We analyzed the differences in EOZs of the two ablation patterns and the correlation between EOZ and magnitude of refractive correction. RESULTS: The mean postoperative EOZs were 17.9 +/- 3.7 mm(2) and 11.4 +/- 3.4 mm(2) after CV and standard LASIK, representing 60% and 40% of the laser-programmed optical zones, respectively (both P < .0001). There was no correlation between the postoperative EOZs and the magnitude of refractive correction for both ablations (all P > .05). In eyes with spherical correction (cylinder < or =0.25 diopters), CV LASIK increased the preoperative EOZ by 3.8 +/- 5.6 mm(2) (P = .018), whereas standard LASIK decreased EOZ by 4.5 +/- 5.2 mm(2) (P = .005). CONCLUSION: CV LASIK created larger corneal topographic EOZs than standard ablation. In eyes with spherical correction, the preoperative EOZ was expanded by CV LASIK and reduced by standard LASIK.     

Combined laser in situ keratomileusis and radial keratotomy for the treatment of moderate to high myopia

PURPOSE: To evaluate the results of combining laser in situ keratomileusis (LASIK) and radial keratotomy (RK) for the correction of moderate to high myopia. SETTING: Corneal Consultants of Colorado, Littleton, Colorado, and International Eye Care Laser Vision Center, Houston, Texas, USA. METHODS: In a retrospective 2-surgeon interventional case series, outcomes in 60 eyes of 41 patients with moderate to high myopia were reported. All eyes had LASIK using a Visx Star S2 or Summit Apex Plus((R)) excimer laser. Residual myopia was treated with RK. RESULTS: Of the 54 eyes corrected for distance, the mean refractive spherical equivalent was -8.09 diopters (D) preoperatively and -0.43 D after LASIK and RK. The mean follow-up was 15.4 months. At the last visit, the uncorrected visual acuity was 20/20 in 22 eyes (41%), 20/25 in 36 eyes (67%), and 20/40 in 51 eyes (94%). No eye lost 2 or more lines of best spectacle-corrected visual acuity. CONCLUSIONS: Many patients previously considered poor refractive surgery candidates because of their degree of myopia or corneal thickness could be offered this safe and effective combined refractive technique.     

Method for optimizing topography-guided ablation of highly aberrated eyes with the ALLEGRETTO WAVE excimer laser

PURPOSE: To evaluate the clinical outcomes of custom topographic neutralizing technique in treating highly aberrated eyes using the WaveLight ALLEGRETTO WAVE Excimer Laser. METHODS: A retrospective consecutive case series of 67 eyes with decentered ablations and 48 eyes with symptomatic small optical zones after previous LASIK underwent topography-guided retreatment with the ALLEGRETTO WAVE. Sixteen keratoconus eyes underwent topographic neutralizing technique photorefractive keratectomy (PRK). The study assessed preoperative and 6-month and 1-year postoperative results regarding best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), topography, and predictability. RESULTS: Sixty-seven eyes with previously decentered optical zones had an improvement of centration from 0.92 mm preoperatively to 0.30 mm postoperatively relative to pupil center (P<.01). Twenty-nine percent of these eyes gained 1 or more lines of BSCVA, whereas 71% had no change in BSCVA. Forty-eight eyes with previously small optical zones had an increase of the central monodioptric optical zone from 3.9 mm to 5.6 mm (P<.01). Nineteen percent of eyes had an improvement of at least 1 line, whereas 75% had no change in BSCVA and 6% lost 1 line. Sixteen keratoconus eyes had custom topographic neutralizing technique PRK as an alternative to penetrating keratoplasty. All eyes had improvement of astigmatism up to 5.00 diopters (D), with a mean change of 1.68+/-1.62 D. Best spectacle-corrected visual acuity was unchanged in 8 (50%) eyes, with 4 (25%) eyes gaining 1 line, 2 (12%) eyes gaining 2 lines, and 2 (12%) eyes losing 1 line of BSCVA at 6 months. CONCLUSIONS: Management of some highly aberrated eyes is now possible with topography-guided ablation using the WaveLight ALLEGRETTO platform and custom topographic neutralizing technique. Safety was acceptable for small optical zone and decentered ablation retreatments. The topography-guided ablation could be an alternative treatment for keratoconus patients if keratoplasty is otherwise indicated. The algorithms for custom topographic neutralizing technique need further refinement.