准分子激光屈光性角膜切削术后角膜地形图分析

目的分析准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ,ＰＲＫ）术后角膜切削区的形态、偏心情况和屈光的稳定性。方法对３１２例（３６６只眼）ＰＲＫ手术患者进行术后１、３和６个月的角膜地形图检查。结果术后１个月切削区中心偏离瞳孔中心的距离为０．２６６ｍｍ,双眼平均偏离瞳孔中心的方向均为鼻上侧。切削区形态平滑型占４９．５％,半环型、钥匙洞型、肾型和哑铃型占４２．９％,中心岛型占６．０％。中心岛型对术后最佳矫正视力影响较大。术后１～３个月角膜屈折力变化较大,高度近视比低度近视回退明显。结论提示ＰＲＫ术中瞄准中心问题非常重要,直接影响术后的效果,同时也应长期随访角膜地形图,进一步观察术后的稳定性。     

PRK切削中心偏离的临床观察

为研究准分子激光屈光性角膜切削术（ＰｈｏｔｏｒｅｆｒａｃｔｉｖｅＫｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）切削中心偏离对角膜散光与欠矫的影响。对ＰＲＫ术后２１０眼行角膜地形图检查后发现，ＰＲＫ切削偏心小于０５０ｍｍ者为３７２％，０５０～１００ｍｍ者为５３３％，１０ｍｍ以上者为９５％，切削偏心平均为０７６ｍｍ，欠矫平均为１４１Ｄ，散光无明显改变。切削偏心能直接导致欠矫的发生，但对角膜散光无明显影响，减小偏心可以避免欠矫的发生。     

应用角膜地形图评价PRK矫正近视散光的疗效

目的以ＰＲＫ矫正近视性散光术后１ａ临床结果和角膜地形图检测结果评价ＰＲＫ矫正近视散光的效果。方法对６１只眼近视散光在－２．００Ｄ以上者应用ＰＲＫ治疗，术后随访１ａ，并对手术前后散光的变化进行角膜地形图比较。结果患者ＰＲＫ术后１ａ检查，其中６０只眼散光在０～－１．００Ｄ之间，角膜切削区中心距瞳孔中心均≤０．５ｍｍ，角膜地形图检测术前△Ｋ值为１．８５±０．５９Ｄ，术后△Ｋ值为０．９０±０．４３Ｄ，显示术后散光下降明显。结论ＰＲＫ治疗散光效果明显，但应解决角膜切削区域偏中心情况。     

近视患者用准分子激光作角膜切削术后角膜地形图的改变

１７例近视患在准分子激光切割术后第一年中进行了计算机辅助的角膜地形图的分析。角膜中央视区进行了自然过渡到周边角膜的切削。在一些眼出现切割偏中心（３眼小于０．５ｍｍ，１０眼为０．５～１．０ｍｍ，３眼为１～１．５ｍｍ，１眼为２．１ｍｍ），说明瞄准光束是非常重要的。有待改进使切削中心位于瞳孔中心。１７眼中的１２眼在ＰＲＫ术后３～７个月内角膜地形图非常稳定，其余的５眼在６～１２个月的随访时，发现中央屈光     

准分子激光角膜切削术后肌性视疲劳与切削偏心的关系

目的：探讨准分子激光角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）后肌性视疲劳与切削偏心的关系。方法，对８例１６只眼近视性屈光不正行ＰＲＫ后随访６～１４个月，视力均在０．８以上且主观接受棱镜矫正的肌性视疲劳者，根据术后与术前的角膜地形图及其相减图的数据，按Ｈｏｌｌａｄａｙ法计算角膜实矫屈光度Ｄ，检测偏离瞳孔中心的切削偏心量ｈ（以ｍｍ为单位）及方向，用公式（棱镜度）δ≈Ｄ     

放射状角膜切开术后残余近视眼的准分子激光角膜切削术

目的探讨准分子激光角膜切削术（ＰＲＫ）矫治放射状角膜切开术（ＲＫ）后残余近视眼的安全性与有效性。方法应用ＣＨＩＲＯＮ公司ＴｅｃｈｏｌａｓＫｅｒａｃｏｒｌ１６型准分子激光机对１６例（２１只眼）ＲＫ后残余近视眼施ＰＲＫ，应用计算机辅助的角膜地形图对手术的有效性与安全性作客观评估。结果１６例（２１只眼）经ＰＲＫ后，裸眼视力提高４～１０行（平均７．５行）；等效球镜的屈光度下降２．５０～６．００Ｄ（平均４．７５Ｄ）；所有术眼的角膜地形图提示角膜中央呈规则圆形变扁区，角膜中央３ｍｍ直径的屈光力平均下降４．２５Ｄ。随访期内（１ａ）所有术眼无明显并发症。结论ＰＲＫ是矫治ＲＫ后残余近视眼安全有效的方法     

准分子激光角膜屈光性手术治疗近视的疗效分析

对准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｃｅｃｔｏｍｙ，ＰＲＫ）和准分子激光原位角膜磨镶术（ｌａｓｅｒｉｎｓｉｔｕｋｅｒａｔｏｍｉｌｅｕｓｉｓ，ＬＡＳＩＫ）治疗近视的疗效进行对比研究。方法，对术前近视度为－１．５０Ｄ－２０．００Ｄ的患者的６００只眼，接近视度分为三组：中低度近视组（－１．５０Ｄ－－６．００Ｄ）２３４只眼，１９４眼行ＰＲＫ手术，４０眼行ＬＡＳＩＫ手术，高     

准分子激光屈光性角膜手术后角膜知觉的改变

目的观察和分析准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）和准分子激光原位角膜磨镶术（ｌａｓｅｒｉｎ－ｓｉｔｕｋｅｒａｔｏｍｉｌｅｕｓｉｓ，ＬＡＳＩＫ）治疗近视后角膜知觉的变化。方法对２３１例（３８７只眼）近视患者施行ＰＲＫ，对４８２例（７９６只眼）施行ＬＡＳＩＫ进行治疗。对术后角膜知觉不同时期的变化进行检查、分析。结果ＰＲＫ和ＬＡＳＩＫ术后早期角膜知觉均明显下降，尤以ＰＲＫ明显。ＰＲＫ术后角膜知觉在术后６个月才能恢复，ＬＡＳＩＫ术后角膜知觉约在术后１个月即恢复。结论ＰＲＫ术后角膜知觉的恢复比ＬＡＳＩＫ慢。     

准分子激光屈光性角膜切削术与激光原位角膜磨镶术治疗中低度近视的对比

目的对准分子激光屈光性角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）和准分子激光原位角膜磨镶术（ｌａｓｅｒａｓｓｉｓｔｅｄｉｎｓｉｔｕｋｅｒａｔｏｍｉｌｌｅｕｓｉｓ，ＬＡＳＩＫ）治疗中、低度近视的疗效进行前瞻性对比研究。材料和方法术前屈光度为－１．２５～－６．００Ｄ的近视５６９只眼，其中１３７只眼接受ＬＡＳＩＫ手术，４３２只眼接受ＰＲＫ手术，随访６－１６个月（平均８．９±２．６个月）。在术后１周、１个月、３个月、６个月和１２个月复查。结果ＬＡＳＩＫ组术后屈光状态较ＰＲＫ稳定，回退幅度较ＰＲＫ小，术后６个月时，ＬＡＳＩＫ组和ＰＲＫ组分别有９４％和８７％屈光度在±１．００Ｄ内（ｐ＜０．０５），分别有８４％和７１％屈光度在±０．５０Ｄ以内（ｐ＜０．０１）。ＬＡＳＩＫ组术后视力恢复较ＰＲＫ快，术后１周的平均裸眼视力超过１．０，术后６个月时，ＬＡＳＩＫ和ＰＲＫ组中裸眼视力０．５或以上者分别占１００％和９４％（ｐ＜０．０１），裸眼视力１．０以上者分别占８６％和７２％（ｐ＜０．０１）。结论ＬＡＳＩＫ不仅适合治疗高度近视，也适合治疗中、低度近视。对于中、低度近视，ＬＡＳＩＫ的疗效优于ＰＲＫ。     

准分子激光角膜切削术后屈光回退伴角膜雾浊再次手术疗效

近视眼准分子激光角膜切削术（ｐｈｏｔｏｒｅ－ｆｒａｃｔｌｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）后，部分病例存在远期屈光回退、角膜雾浊（Ｈａｚｅ）影响疗效。我院ＰＲＫ中心于１９９６年８月～１９９７年２月对６例８眼ＰＲＫ术后屈光回退伴角膜Ｈａｚｅ病例行再次ＰＲＫ治疗，效果满意，总结报道如下。１材料与方法１．１临床资料８眼病例为我院ＰＲＫ中心治疗后随访１１．２±１．４ｍｏ出现屈光回退伴角膜Ｈａｚｅ的近视眼患者，男６眼，女２眼，年龄２４．０±４．０６ａ（１９～４０ａ）。首次ＰＲＫ术前平均等值球镜屈光度为一…     

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.     

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.     

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.     

Ablation centration in myopic laser in situ keratomileusis. comparing the Visx S3 ActiveTrak and the Visx S2

PURPOSE: To compare ablation centration and outcome measurements in myopic laser in situ keratomileusis (LASIK) using the eye-tracking Visx S3 ActiveTrak and the nontracking Visx S2 excimer lasers. SETTING: University-based refractive surgery practice. METHODS: In a retrospective study, 71 consecutively treated myopic eyes that had LASIK with the Visx Star S3 ActiveTrak were compared to 71 control-matched eyes treated with the Visx Star S2 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: The myopia ranged from -1.50 to -11.25 diopters (D) and the cylinder, from +0.25 to +2.75 D. Ninety-four of 142 eyes (66%) were available for analysis at 3 months; 50 eyes could be used to analyze ablation centration. At 3 months, the mean decentration of the ablation zone from the entrance pupil was 0.22 mm +/- 0.20 (SD) in tracked eyes (n = 25) and 0.21 +/- 0.26 mm in nontracked eyes (n = 25) (P =.88). Three eyes (12%) in the tracked group were decentered 0.5 to 1.0 mm, and 1 eye (4%) in the nontracked group was decentered more than 1.0 mm. All other eyes were decentered less than 0.5 mm. There was an association in the tracked group between greater decentrations and higher levels of myopia (r = 0.67), but this association did not exist in the nontracked group (r = -0.03). CONCLUSION: Comparable ablation centration as well as visual and refractive outcomes can be achieved with and without active eye tracking during myopic and astigmatic myopic LASIK.     

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.     

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.     

Rigid gas-permeable contact lens fitting in LASIK patients for the correction of multifocal corneas

BACKGROUND: Laser in situ keratomileusis (LASIK) has recently become the most commonly performed refractive surgery procedure. Results are promising in correcting low to moderate myopia. Most complications occur during the surgeon's learning curve. One of the complications is a decentration of the ablated area that causes monocular diplopia and a nocturnal halo phenomenon due to a multifocality of the corneal surface overlying the entrance pupil. The corneal shape is significantly altered after LASIK. We evaluate the efficacy of rigid gas-permeable contact lens designs and fitting techniques used in eight eyes with multifocal LASIK ablations to correct haloes and impaired night vision complaints. METHODS: We used large-diameter tetra-curved rigid gas-permeable (RGP) contact lenses for visual recovery in eight eyes of seven LASIK patients. We used the power on the transition zone of the corneal topographic map, 0.2 mm outside the ablated refractive area, for selection of the back optic zone radius of the RGP contact lenses. Procedures for lens fitting are described. Visual acuity (high-contrast logarithm of the minimum angle of resolution, LogMAR) was measured before- and 6 months after contact lens fitting. RESULTS: Large-diameter tetra-curve RGP lenses with a mean diameter of 11.85 (SD 0.16) mm were successfully used in LASIK patients with multifocal corneas. Mean best spectacle-corrected visual acuity was +0.3 LogMAR (SD 0.19; in Snellen equivalent, 20/40) and improved significantly with the contact lenses to +0.08 LogMAR (SD 0.11; in Snellen equivalent, 20/25, P=<0.01). During the follow-up period of 16.7 months, the average daily wearing time of the lenses was 12.5 h. Contact lenses with a standard geometry were not useful due to excessive movement and inadequate centration. CONCLUSIONS: Contact lenses with large diameters, in combination with selection of the back optic zone radius 0.2 mm peripheral of the refractive ablation zone, facilitate contact lens fitting to restore best-corrected visual acuity in LASIK patients with multifocal corneas.     

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.     

角膜地形图分析准分子激光原位角膜磨削术偏心切削

目的用即时角膜地形图评估准分子激光原位角膜磨削术（LASIK）后偏心切削——治疗偏移和漂移。方法对LASIK术后1个月的100只眼(52例)的即时角膜地形图进行分析,确定角膜切削中心偏移入射瞳孔中心的距离及在切削过程中眼球运动引起的漂移程度,并与最佳矫正视力进行比较。结果平均治疗偏移量为0.53mm±0.28mm。49眼(49%)切削中心位于入射瞳孔中央0.5mm范围内,切削中心向上方偏移的68眼(68%)。平均漂移指数为0.25±0.22。漂移指数与最佳矫正视力有正相关关系。治疗偏移与最佳矫正视力无统计学意义。结论即时角膜地形图可用于评估和鉴别LASIK术中角膜切削中心的定位偏移与切削过程中眼球运动引起的漂移。高漂移会对术后视功能造成消极影响。     

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.