PRK、LASIK术后角膜地形图的变化对视力恢复的影响

目的：探讨准分子激光角膜切削术（photorefractive keratectomy,PRK)与准分子激光原位角膜磨镶术（laser insitu keratomileusis,LASIK)前后角膜地形图的变化及其与裸眼视力的关系。方法：采用EyeSys2000型角膜地形图系统测量PRK、LASIK术前及术后10天，1、3、6、12及24个月时的角膜地形图并记录同期的视力。结果：角膜地形图显示术后切削形态随着时间延长，趋于规则，Simk的差值和等效值，PRK组和LASIK组术前与术后相比都有显著性差异，术后偏心距离均在1.00mm内，术后裸眼眼力≥0．6，结论：在低、中度近视中，LASIK术后的偏心程度较PRK的稍重，引起裸眼视力偏低。     

主动眼球跟踪准分子激光原位角膜磨镶术后光学切削区偏中心的临床研究

准分子激光屈光性角膜切削术(photorefractive keratectomy，PRK)及准分子激光原位角膜磨镶术(laser in situ keratomileusis，LASIK)后，激光光学切削区中心与瞳孔中心的吻合程度，会直接影响手术效果。术后光学切削区中心偏离瞳孔中心越远，近视矫正效果越差，有些患者甚至会出现单眼复视、眩光、光晕等症状。主动眼球跟踪系统的问世，为提高术中激光束定位切削的精确性创造了条件，本研究借助计算机辅助角膜地形图分析系统，分析主动眼球跟踪近视LASIK术后光学切削区偏中心程度，评价这一系统的精确性。     

LASIK术后切削中心的角膜地形图分析

目的：探讨准分子激光角膜原位磨镶术（laser in situ keratomileusis,LASIK）切削中心对术后最佳矫正视力的影响及与术前屈光度的关系。方法：应用计算机辅助角膜地形图仪对175例（340眼）LASIK术后随访6月以上的术前、术后角膜地形图进行检测、分析，测量准分子激光切削中心相对瞳孔中心的距离，并与最佳矫正视力、术前屈光度进行比较。结果：切削区中心相对瞳孔中心偏离小于0．5mm者242眼（71．2％），0．5－1．0mm者77眼（22．6％），大于1．0mm者21眼（6．2％）。术后最佳矫正视力下降1－2行者，偏心量小于1．0mm，发生率为7．8％；大于1．0mm发生率为38．1％，切削中心偏移致术后最佳矫正视力下降，与术前屈光度无关。结论：LASIK前后角膜地形图检查和分析能清楚地显示角膜表面形态变化及定量评估切削区偏中心问题。严重的偏中心切削是影响术后最佳矫正视力的重要因素。     

分区切削模式在LASIK治疗超高度近视的应用

目的评价对角膜相对较薄的超高度近视,应用分区切削模式进行LASIK治疗的临床效果。方法对95例(185眼)超高度近视,因选择6.0 mm直径的切削区,剩余角膜厚度小于250μm,而进行LASIK分区切削治疗,分区切削分为2～3区,切削光区4.7～6.0 mm。随访时间6～20月,观察手术前后的屈光状态、裸眼视力、矫正视力、角膜地形图及并发症的发生情况。结果术后1月视力达到最好并趋于稳定,所有患者的裸眼视力均较术前提高,术后3月183眼(98.92%)裸眼视力超过或等于术前最佳矫正视力。屈光回退47眼(25.41%),术后眩光51眼(27.57%),分析手术后角膜地形图,切削过度区光滑,无偏心切削。与标准手术相比可节省角膜厚度20%～25%,视力、屈光度变化与分区多少及近视度数有关。少数患者出现的眩光、夜视力下降等并发症,1个月后减轻或消失,角膜地形图均为正常负性形态。结论LASIK分区切削模式是对角膜相对较薄的超高度近视进行激光治疗有效安全的方法。可节省角膜组织,具有安全可靠,稳定性、可预测性强的临床效果。     

LASIK治疗近视后切削中心的角膜地形图观察

目的评价准分子激光角膜原位磨镶术(Laser in situ keratomileusis,LASIK)矫治近视眼术后切削中心的偏移对术后最佳矫正视力的影响.方法应用角膜地形图仪对185例(356眼)LASIK术后随访6个月以上的术前、术后角膜地形图进行观察分析,测量准分子激光切削中心相对于瞳孔中心的距离、方向,并用视功能进行比较.结果激光切削中心相对于瞳孔中心的距离平均偏心值为0.38±0.26mm;其中偏离瞳孔中心0.5mm以内为263眼(73.9%),0.5～1.0mm为85眼(23.9%),1.0～1.2mm者为8眼(2.2%),切削中心位于鼻侧者为320眼(89.9%).偏中心切削致术后最佳矫正视力下降1～3行偏心量≤0.5mm中、小光区切削9眼,偏心量＞0.5mm为27眼.结论严重的偏中心切削将导致术后裸眼视力和最佳矫正视力下降,准确的切削中心定位和在条件允许情况下,适当扩大切削直径以及完整的角膜瓣对LASIK术后的效果应是十分重要的.     

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。     

准分子激光原位角膜磨镶术中不全角膜瓣后角膜地形图的改变

目的探讨准分子激光原位角膜磨镶术(laser insitu keratomileusis,LASIK)中不全角膜瓣后角膜地形图的变化规律。方法回顾性研究17眼采用hansatome角膜板层刀行LASIK手术的患者,因术中不全角膜瓣而未发射激光的发生情况及不全角膜瓣后Orbscan角膜地形图、视力及屈光度的改变。结果术中不全角膜瓣的发生率为0.29%。不全角膜瓣切削前后视力、屈光度及角膜前后表面曲率均无明显改变(P>0.05)。结论LASIK术中不全角膜瓣的发生不会引起角膜地形图的改变,再次行LASIK并不影响疗效。     

近视眼准分子激光原位角膜磨镶术后角膜非球面性的改变

目的 研究近视眼准分子激光原位磨镶术（laser in situ keratomileusis，LASIK）后角膜非球面性的改变。方法 对93例近视眼患者（148眼）LASIK术后进行回顾性分析．用Orbscan-Ⅱ角膜地形图仪测量角膜在LASIK术前和术后非球面参数Q值、角膜曲率simk值（K）、切削的偏心值。分析Q值、角膜曲率改变（△K），△Q与预期矫正值（SE）、AK之间的相关性，以及术后。值与偏心量之间的相关性。结果 角膜形状从术前扁长型（Q〈0）到术后为扁圆型（Q〉0）；角膜曲率变平；AQ与SE、AK之间存在相关性（分别为r=0．771，P〈0．01和r=0．783，P〈0．01），但术后Q值与偏心量之间无相关性（r=0．068，P〉0．05）。结论 近视患者LASIK术后角膜非球面参数Q明显增大，变化量与预期矫正值、曲率变化量相关。     

准分子激光原位角膜磨镶术双面切削法治疗高度近视远期疗效

目的 探讨准分子激光原位角膜磨镶术（LASIK）矫正高度近视角膜厚度不足时的治疗方法。方法 制作以角膜鼻侧或颞侧为蒂部的角膜瓣,角膜瓣翻转后将20%拟矫正手术量切削在角膜瓣基质面,80%手术量切削于角膜基质床。随访24～30月共28眼。结果 术后末次随访裸眼视力≥1.0共23眼（82.1%）,≥0.8共26眼（92.8%）。术后角膜地形图无明显的偏心及散光形成,未见明显角膜瓣并发症。结论 LASIK角膜瓣翻转后激光切削为高度近视角膜厚度不足的患者提供了一种完全矫正方法。手术操作的要点是要保证切削区中心的重合,并注意缩短手术时间以保护角膜上皮。     

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     

Functional optical zone of the cornea

PURPOSE: When keratorefractive surgery is used to treat a central corneal diameter smaller than the resting pupil, visual symptoms of polyopia, ghosting, blur, haloes, and glare can be experienced. Progress has been made to enlarge the area of surgical treatment to extend beyond the photopic pupil; however, geometric limitations can pose restrictions to extend the treatment beyond the mesopic pupil diameter and can lead to impediments in night vision. The size of the treated area that has achieved good optical performance has been defined as the functional optical zone (FOZ). In this study the authors developed three objective methods to measure the FOZ. METHODS: Corneal topography examination results from 1 eye of 34 unoperated normal eyes and 32 myopic eyes corrected by laser in situ keratomileusis (LASIK) were evaluated in three ways. First, a uniform axial power method (FOZ(A)) assessed the area of the postoperative cornea that was within a +/-0.5-D window centered on the mathematical mode. Second, FOZ was determined based on the corneal wavefront true RMS error as a function of the simulated pupil size (FOZ(R)). Third, FOZ was determined from the radial MTF, established at the retinal plane as a function of pupil size (FOZ(M)). RESULTS: Means for each of the FOZ methods (FOZ(A), FOZ(R), and FOZ(M)) were 7.6, 9.1, and 7.7 mm, respectively, for normal eyes. For LASIK-corrected eyes, these means were 6.0, 6.9, and 6.0 mm. Overall, an average decrease of 1.8 mm in the functional optical zone was found after the LASIK procedure. Correlations between the FOZ methods after LASIK showed acceptable and statistically significant values (R = 0.71, 0.70, and 0.61; P < 0.01). CONCLUSIONS: These methods will be useful to more fully characterize corneal treatment profiles after keratorefractive surgery. Because of its ease of implementation, direct spatial correspondence to corneal topography, and good correlation to the other more computationally intensive methods, the semiempiric uniform axial power method (FOZ(A)) appears to be most practical in use. The ability to measure the size of the FOZ should permit further evolution of keratorefractive surgical lasers and their algorithms to reduce the night vision impediments that can arise from functional optical zones that do not encompass the entire mesopic pupil.     

Wavefront analysis in post-LASIK eyes and its correlation with visual symptoms, refraction, and topography

PURPOSE: To evaluate the information assessed with the LADARWave wavefront measurement device and correlate it with visual symptoms, refraction, and corneal topography in previously LASIK-treated eyes. PARTICIPANTS: One hundred five eyes (58 patients) of individuals who underwent LASIK surgery were evaluated. DESIGN: Retrospective, noncomparative case series. MAIN OUTCOME MEASURES: Complete ophthalmologic examination, corneal topography, and wavefront measurements were performed. Correlations were made between the examinations and symptoms. METHODS: Wavefront measurements were assessed with the LADARWave device. Manifest, cycloplegic refraction, and topographic data were compared with wavefront refraction and higher order aberrations. Visual symptoms were correlated to higher order aberrations in 3 different pupil sizes (5-mm, 7-mm, and scotopic pupil size). Pearson's correlation coefficient and generalized estimating equations were used for statistical analysis. RESULTS: In post-LASIK eyes, wavefront refraction components were poorly correlated to manifest and cycloplegic components. The comparison between manifest, cycloplegic, and wavefront refraction with total amount of higher order aberrations showed no strong correlation. The comparison between topography and manifest, cycloplegic, and wavefront refraction did not show strong correlation. Visual symptoms analysis showed correlation of double vision with total coma and with horizontal coma for the 5-mm and 7-mm pupil size; correlation between starburst and total coma for the 7-mm pupil size; and correlation of double vision with horizontal coma, glare with spherical aberrations and with total aberrations, and starburst with spherical aberrations for the scotopic pupil size. Scotopic pupil size had a positive association with starburst and a negative association with double vision. CONCLUSIONS: The LADARWave wavefront measurement device is a valuable diagnostic tool in measuring refractive error with ocular aberrations in post-LASIK eyes. A strong correlation between visual symptoms and ocular aberrations, such as monocular diplopia with coma and starburst and glare with spherical aberration, suggest this device is valuable in diagnosing symptomatic LASIK-induced aberrations. Horizontal coma was correlated with double vision, whereas vertical coma was not.     

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.     

Night vision disturbances after corneal refractive surgery

A certain percentage of patients complain of “glare” at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, “night vision disturbances.” The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.     

Quality of vision and patient satisfaction after LASIK

PURPOSE: The purpose of this article is to review the literature and find characteristics that lead to improved patient satisfaction and better quality of vision. RECENT FINDINGS: Flatter preoperative corneal curvature is a risk factor for starbursts after laser-assisted in situ keratomileusis (LASIK). Pupil size has not been found to be correlated with night vision symptoms. Wavefront-guided ablations reduce higher-order aberrations in comparison with traditional LASIK. Night vision symptoms are correlated with younger age, greater correction/increased ablation depth, enhancement, and decreased ablation diameter. Contrast sensitivity has been found to initially decrease after LASIK, returning to baseline 6 to 12 months postoperatively. SUMMARY: LASIK has quickly become the refractive procedure of choice around the world. Quality of vision and patient satisfaction after LASIK can be difficult to assess because of the many variables that must be considered to accurately measure these endpoints. Preoperative characteristics such as: increased patient age, decreased corneal toricity, or increased pupil size reduce patient satisfaction. Intraoperative factors like decentration, ablation-zone size, active eye tracking, and wavefront guided ablations affect quality of vision. Finally, postoperative factors such as night vision symptoms, reduced contrast sensitivity, and re-treatment can lead to a decline in patient satisfaction. Eliminating or limiting these variables may lead to increased patient satisfaction and higher quality of vision after LASIK.     

Correlation of aberrations with visual symptoms using wavefront analysis in eyes after laser in situ keratomileusis

PURPOSE: To evaluate the information assessed with the Alcon LADARWave wavefront measurement device and correlate it with visual symptoms in eyes previously treated with laser in situ keratomileusis (LASIK), and to analyze the influence of scotopic pupil size on visual symptoms. METHODS: One hundred and five eyes of 58 patients who underwent LASIK were evaluated. Wavefront measurements were assessed using the Alcon LADARWave device. Visual symptoms were correlated to higher order aberrations in three different pupil sizes (5 mm, 7 mm, and scotopic pupil size). Generalized estimating equations were used for statistical analysis. RESULTS: In eyes after LASIK, visual symptoms analysis showed positive correlation of double vision with total coma and with horizontal coma for the 5-mm and 7-mm pupil sizes, negative correlation between starburst and total coma for the 7-mm pupil size, positive correlation of double vision with horizontal coma, and glare and starburst with spherical aberration and with total aberrations. Scotopic pupil size had a positive association with starburst and negative association with double vision. CONCLUSION: The LADARWave wavefront measurement device is a valuable diagnostic tool in measuring ocular aberrations in eyes after LASIK. A strong correlation between visual symptoms and ocular aberrations, such as monocular diplopia with coma, and starburst and glare with spherical aberration, suggest this device is valuable in diagnosing symptomatic LASIK-induced aberrations. Horizontal coma was correlated with double vision, while vertical coma was not, demonstrating a greater sensitivity with horizontally oriented multifocality.     

Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography.

PURPOSE: To demonstrate the functional vision and corneal changes following laser in situ keratomileusis (LASIK) determined by contrast sensitivity, glare testing, and corneal topography. SETTING: University of Texas Medical School, Houston, Texas, USA. METHODS: Seven patients ranging in age from 20 to 61 years who had bilateral LASIK were evaluated preoperatively and 1 day, 1 week, and 1 and 6 months postoperatively. Visual acuity, using letters on the Baylor Visual Acuity Testor (BVAT) at 98% (standard acuity) and 13% contrast, and the contrast threshold were determined at 3 light levels (darkness, medium brightness acuity testor [BAT], high BAT). Pupil sizes were measured at each level, and corneal topography was performed at each visit. RESULTS: The greatest changes were found 1 day postoperatively: The contrast threshold worsened by a mean of 0.6 lines +/- 1.0 (SD) (P = .05) in darkness, 0.4 +/- 0.7 lines (P = .05) at medium BAT, and 0.8 +/- 0.7 lines (P = .002) at high BAT. The 98% contrast acuity decreased a mean of 1.4 +/- 1.6 lines (P = .01) in darkness, 1.0 +/- 2.0 lines (P = .09) at medium BAT, and 0.8 +/- 2.3 lines (P = .22) at high BAT. The 13% contrast acuity decreased a mean of 2.2 +/- 2.6 lines (P = .01) in darkness, 1.3 +/- 1.9 lines (P = .02) at medium BAT, and 1.4 +/- 2.5 lines (P = .07) at high BAT. The predicted corneal acuity (PCA) obtained from corneal topography decreased by a mean of 3.3 +/- 3.1 lines (P = .002), and the asphericity (Q-value) increased by an average of +0.35 +/- 0.67 (P = .07). All values returned to the preoperative levels by 1 week except PCA, asphericity, visual acuity at 13%, and contrast threshold in darkness, which improved slightly but had not returned to baseline by 6 months. The 98% contrast acuity at medium BAT improved by 0.2 +/- 1.0 lines (P = .34) and 0.3 +/- 0.8 lines (P = .16) at high BAT at 1 month. The 98% contrast acuity values remained 0.3 lines over baseline through 6 months. Corneal topography showed that all corneas became oblate after LASIK to a mean Q-value of +0.47 +/- 0.40 (P = .0001) and PCA was decreased by 1.6 +/- 1.1 lines (P = .0002) at 6 months. CONCLUSIONS: Functional vision changes do occur after LASIK. The optical quality of the cornea is reduced and the asphericity becomes oblate. Changes in functional vision worsen as the target contrast diminishes and the pupil size increases. These findings indicate that the oblate shape of the cornea following LASIK is the predominant factor in the functional vision decrease.     

Topographical Evaluation of the Decentration of Orthokeratology Lenses

Purpose: To evaluate the amount of lens decentration and various factors affecting decentration after orthokeratology lens wear and to observe the effect of decentration on the visual functions. Methods: Two kinds of orthokeratology lenses were fitted to 270 eyes of 135 patients [initial mean refractive error: (-3.98±1.51 )D]. Humphery Instruments ATLAS 990 was used for the computer-assisted analysis of corneal topographical maps. The examination of corneal topography was performed on patients before and after 6 months of wearing orthokeratology lenses. The amount of decentration of orthokeratology lenses was measured by finding the distance between center of optic zone and the pupil center. The factors influencing the amount of decentration were analyzed, including the initial refraction error, astigmatism, keratometry values, corneal eccentricity, and the diameter of lens. Visual symptoms including monocular diplopia, glare around lights were recorded to evaluate the effects of decentration on visual functions. Results: The mean amount of decentration was (0.49±0.34) mm after one night's wear. The mean amount of decentration after 1 month, 3 months and 6 months was (0.57±0.41) mm, (0.55±0.48) mm and (0.59±0.39) mm, respectively. After one month, the amount of decentration was less than 0.50 mm in 51.1% eyes, 0.50-1.0 mm in 35.6% eyes and more than 1.00 mm in 13.3% eyes. The direction of decentration of more than 0.50 mm was mainly in the temporal quadrant (48.5%). Patients with greater initial astigmatism and smaller lenses showed greater decentration (P<0.05). There was no statistically significant difference in decentration between the two groups with different corneal eccentricities and keratometry values (P>0.05). The amount of decentration was greater in patients who complained of monocular diplopia and glare. Conclusions: The amount of decentration of orthokeratology depends on the initial refractive error, astigmatism and the design of orthokeratology lenses. Improvement in fitting technology and lens design can lead to reduced incidence of decentration and visual symptoms. Eye Science 2005;21:132-135.     

Quality of vision after laser in situ keratomileusis: influence of dioptric correction and pupil size on visual function

PURPOSE: To determine the influence of pupil size and the amount of ablation on visual performance and on the patient's perception of glare or halo after laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. METHODS: This study included a random cross-section of 50 eyes of 32 patients with "uniform" topography at least 6 months after LASIK and 51 eyes of 28 patients who had normal corneas. Each LASIK patient completed a survey rating adverse effects such as symptoms of night glare and halo. Pupil diameter and best spectacle-corrected visual acuity (BSCVA) were measured under photopic and scotopic conditions. Contrast sensitivity was measured with an MCT 8000 (Vistech Consultants, Inc.) under daytime and nighttime and with night glare conditions. A Technomed C-scan (Technomed Technology) was performed, and the potential corneal visual acuity (PCVA) was calculated after the settings for the pupil size were changed to the values measured under bright-light or dim-light conditions. RESULTS: No significant difference was found between the post-LASIK and normal cornea groups in photopic or scotopic BSCVA (P>.05). In cases of moderate myopia, the post-LASIK group had decreased PCVA and contrast sensitivity (P<.05). In cases of high myopia, the post-LASIK group had decreased contrast sensitivity at spatial frequencies of 1.5 cycles per degree (cpd) under daytime conditions and 3 cpd under nighttime conditions (P<.05). Glare or halo symptoms did not correlate with scotopic BSCVA, PCVA, or nighttime contrast sensitivity with or without glare (P>.05). Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity under scotopic or photopic conditions (P>.05). In moderate myopia, the amount of attempted correction of the spherical equivalent (SE) was correlated with halo symptoms (P<.05; adjusted r(2) = 0.17). In high myopia, the amount of attempted astigmatism correction was correlated with the development of glare symptoms (P<.05; adjusted r(2) = 0.16). CONCLUSIONS: There was a decrease in contrast sensitivity in post-LASIK eyes. The amount of attempted correction of the SE or astigmatism was correlated with the development of glare and halo symptoms. Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity in post-LASIK patients with "uniform" topography who had scotopic pupils not larger than 7.0 mm.     

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.