Increased higher-order optical aberrations after laser refractive surgery: a problem of subclinical decentration

PURPOSE: To study the clinical and theoretical effects of subclinical decentrations on the optical performance of the eye after photorefractive laser surgery. SETTING: Department of Ophthalmology, University of Dresden, Dresden, Germany. METHODS: Ocular aberrations were determined before and 1 month after uneventful photorefractive keratectomy (PRK) with the Multiscan laser (Schwind) in 10 eyes of 8 patients. The corrections ranged from -2.5 to -6.0 diopters, and ablation zones of 6.0 mm and larger were used. The measured wavefront errors were compared to numerical simulations using the individually determined decentrations and currently used ablation profiles. RESULTS: The PRK-induced aberrations were significantly greater than the preoperative aberrations. The numerically calculated increase in the higher-order optical aberrations correlated with the clinical results, demonstrating a major increase in coma- and spherical-like aberrations. Subclinical decentration (less than 1.0 mm) was found to be a major factor in increased coma-like and spherical-like aberrations after corneal laser surgery. CONCLUSION: To minimize higher-order optical errors, special efforts to center the ablation zone are necessary; for example, by eye-tracking systems that consider the visual axis.     

准分子激光原位角膜磨镶术治疗近视后眼高阶像差变化的研究

目的探讨光学区大小对准分子激光原位角膜磨镶术（LASIK）治疗近视后眼高阶像差的影响。方法将接受LASIK治疗的近视者236例（461只眼）分为高、中、低度近视组,每组根据激光切削光学区直径不同（5．75、6．00、6．25和6．50mm）分为Ⅰ～Ⅳ亚组。术前和术后6个月用波阵面像差仪测量眼的像差。用方差分析和q检验分析手术前后各组内不同亚组间在瞳孔直径为4．00、5．00、6．00mm时眼总高阶像差、水平彗差、垂直彗差和球差的差异。结果术前各组内不同亚组间眼高阶像差差异无统计学意义（P〉0．05）。术后6个月,各组内不同亚组间眼总高阶像差和球差差异有统计学意义（P〈0．05）,较大光学区亚组低于较小光学区亚组。高度近视组在不同瞳孔直径时差异均有统计学意义（P〈0．05）,低度近视组在瞳孔直径为6．00mm时差异有统计学意义（P〈0．05）;瞳孔直径为6．00mm时,高度近视组各亚组间差异均有统计学意义（P〈0．05）,低度近视组在Ⅰ、Ⅳ亚组间差异有统计学意义（P〈0．05）。各组内不同亚组间水平彗差和垂直彗差差异均无统计学意义（P〉0．05）。结论光学区大小影响LASIK治疗近视后眼总高阶像差和球差,较大光学区组低于较小光学区组,在治疗高度近视时影响更加明显。     

Genetics of diabetic retinopathy

The purpose was to investigate the effect of decentered ablation in myopic corneal refractive surgery by simulation. Wavefront aberrations in a small pupil area (radius: 2 mm) for photopic vision and in a large pupil area (radius: 3 mm) for mesopic vision with simulated refractive surgery were analyzed using Zernike polynomials. Radii of ablation were 3, 2.5 and 2 mm. Decentrations of ablation were 0 mm and 0.5 mm. Change of the surface shape by ablation was considered a perturbation, while Gullstrand’s schematic eye was used as un-perturbed optics. For photopic vision, wavefront aberrations were about the same as with unperturbed optics. For mesopic vision, the results were heavily dependent on the radius of ablation area. When the radius was 3 mm, wavefront aberrations did not increase very much compared to un-perturbed optics. When the radius was smaller than 3 mm, spherical aberration was induced by centered ablations, and coma was also induced by decentered ablations. In conclusion, small ablation areas or subclinical decentrations of ablations could cause serious amounts of wavefront aberrations to the optics of the eye in the simulations.     

Higher-order wavefront aberrations induced by small ablation area and sub-clinical decentration in simulated corneal refractive surgery using a perturbed schematic eye model

The purpose was to investigate the effect of decentered ablation in myopic corneal refractive surgery by simulation. Wavefront aberrations in a small pupil area (radius: 2 mm) for photopic vision and in a large pupil area (radius: 3 mm) for mesopic vision with simulated refractive surgery were analyzed using Zernike polynomials. Radii of ablation were 3, 2.5 and 2 mm. Decentrations of ablation were 0 mm and 0.5 mm. Change of the surface shape by ablation was considered a perturbation, while Gullstrand's schematic eye was used as un-perturbed optics. For photopic vision, wavefront aberrations were about the same as with un-perturbed optics. For mesopic vision, the results were heavily dependent on the radius of ablation area. When the radius was 3 mm, wavefront aberrations did not increase very much compared to un-perturbed optics. When the radius was smaller than 3 mm, spherical aberration was induced by centered ablations, and coma was also induced by decentered ablations. In conclusion, small ablation areas or subclinical decentrations of ablations could cause serious amounts of wavefront aberrations to the optics of the eye in the simulations.     

Improvement in photorefractive corneal laser surgery results using an active eye-tracking system

PURPOSE: To study the advantage of modern eye-tracking systems for photorefractive surgery. SETTING: Department of Ophthalmology, University of Zurich, Zurich, Switzerland. METHODS: Photorefractive surgery (photorefractive keratectomy and laser in situ keratomileusis) for myopia and myopic astigmatism was performed in 40 eyes with a commercially available medical excimer laser system. The eyes were selected retrospectively from a larger group of patients treated at 1 clinic. In 20 eyes, the ablation was centered on the entrance pupil using the active, video-based, eye-tracking system (sampling frequency 50 Hz) of the laser. During laser treatment in the nontracker group (20 eyes), the active eye-tracking system was switched off and centration was done manually by the surgeon. Preoperatively and 1 and 3 months after surgery, the patients had a standard ophthalmic examination as well as wavefront analysis by means of a custom-designed wavefront analyzer. RESULTS: After surgery, the visual acuity was significantly better (P <.05) in patients treated with the eye tracker. The increase in coma-like (relative increase factor 0.4) and spherical aberrations (relative increase factor 1.1) was significantly smaller in these patients than in those in the nontracker group (spherical equivalents of 3.9 and 5.1, respectively; P <.05). The refractive outcome, however, was not significantly different in sphere and cylinder. CONCLUSION: The use of active eye tracking appeared to improve the optical and visual outcomes but did not affect the refractive outcome after photorefractive laser surgery.     

Conservation of corneal tissue with wavefront-guided laser in situ keratomileusis

PURPOSE: To determine whether corneal tissue can be conserved with wavefront-guided ablation compared to conventional surgery with a larger ablation zone for attempted prevention of glare and halo. SETTING: Department of Ophthalmology, Ilsan Paik Hospital, Inje University, Korea. METHODS: This prospective study was composed of 2 parts: First, 40 eyes of 20 patients were studied to determine whether a larger optical ablation could be beneficial in prevention of glare after conventional laser in situ keratomileusis (LASIK) surgery. One eye in each patient was treated with a 6.00 mm optical zone, and the other with a 6.25 mm optical zone. Second, 20 eyes of 10 patients with a higher-order root mean square (RMS) value of 0.3 or greater were evaluated to learn whether a wavefront-guided ablation could be as effective as a larger conventional optical ablation. One eye in each patient was treated by conventional LASIK surgery with a 6.25 mm optical zone, and the other eye was treated by wavefront-guided LASIK surgery with a 6.00 mm optical zone. All patients were analyzed with a WASCA analyzer (Carl Zeiss Meditec) preoperatively, and 1 month and 3 months after surgery. RESULTS: Higher-order aberrations including coma, spherical aberration, and higher-order RMS were statistically significantly increased after conventional surgery with both a 6.00 mm and 6.25 mm optical zone. High-order aberrations including comaer- and spherical aberration after conventional surgery with 6.25 mm zone were statistically significantly increased. However, coma and higher-order RMS did not show a statistically significant increase between pre-LASIK and post-LASIK in wavefront-ablated eyes with a 6.00 mm optical zone. CONCLUSION: Wavefront ablation showed less increase of coma and higher-order RMS regardless of a smaller optical zone. This finding might provide a clinical clue for an advantage of wavefront-guided ablation from the standpoint of corneal tissue conservation.     

Topography-guided treatment of decentered laser ablation using LaserSight's excimer laser

PURPOSE: To assess the efficacy of topography-guided laser ablation for correction of previously decentered laser ablation using LaserSight's excimer laser. METHODS: Re-treatment was performed to correct decentered ablation using LaserSight's excimer laser for 18 patients who previously underwent LASIK surgery for myopia correction in both eyes. For each patient, only the decentered eye was re-treated while the other asymptomatic eye forms a control group for this study. Measurements were conducted on ablation center, best spectacle-corrected visual acuity (BSCVA), contrast sensitivity and corneal aberrations pre- and post-operatively. RESULTS: For the retreated 18 eyes, the mean decentration was significantly reduced from 1.32+/-0.28mm to 0.61+/-0.23mm post-operatively (t=16.24, p<0.001), and with a significant improvement in mean BSCVA from 0.08+/-0.09 logMAR to 0.01+/-0.11 logMAR (t=4.58, p<0.001). The post-operative contrast sensitivity at the spatial frequencies (SF) of 1.00 and 0.70 was significantly improved (p<0.05 for both SFs). Corneal higher-order aberrations (HOAs), including the coma-like aberrations and spherical aberration, were decreased. In comparing the measurements for the retreated group to those for the control group, no significant differencewas found either in decentration or in BSCVA, but the contrast sensitivity at 0.70 was lower and the level of corneal aberrations was higher. CONCLUSIONS: Topography-guided ablation with LaserSight excimer laser is effective to correct decentered ablation. However, the re-treated eye is still inferior to the eye with originally centered ablation in corneal optical quality or visual performance.     

Aberrations induced in wavefront-guided laser refractive surgery due to shifts between natural and dilated pupil center locations

PURPOSE: To determine the aberrations induced in wavefront-guided laser refractive surgery due to shifts in pupil center location from when aberrations are measured preoperatively (over a dilated pupil) to when they are corrected surgically (over a natural pupil). SETTING: Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA. METHODS: Shifts in pupil center were measured between dilated phenylephrine hydrochloride (Neo-Synephrine [2.5%]) and nonpharmacological mesopic conditions in 65 myopic eyes treated with wavefront-guided laser in situ keratomileusis (Technolas 217z, Bausch & Lomb). Each patient's preoperative and 6-month postoperative wave aberrations were measured over the dilated pupil. Aberrations theoretically induced by decentration of a wavefront-guided ablation were calculated and compared with those measured 6 months postoperatively (6.0 mm pupil). RESULTS: The mean magnitude of pupil center shift was 0.29 mm +/- 0.141 (SD) and usually occurred in the inferonasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the higher-order postoperative root-mean-square wavefront error that could be due theoretically to pupil center decentrations was highly variable (mean 0.26 +/- 0.20 mm). There was little correlation between the calculated and 6-month postoperative wavefronts, most likely because pupil center decentrations are only 1 of several potential sources of postoperative aberrations. CONCLUSIONS: Measuring aberrations over a Neo-Synephrine-dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront-guided ablation in the superotemporal direction and an induction of higher-order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye will reduce the potential for inducing aberrations due to shifts in pupil center.     

Relative contribution of central and peripheral aberrations to overall high order corneal wavefront aberration

PURPOSE: To analyze the influence of specific combinations of corneal high order aberrations on the optical image quality of the cornea before and after photorefractive keratectomy (PRK) for low to high myopia and myopic astigmatism. METHODS: Corneal topography was obtained for 80 eyes that underwent PRK using a scanning-spot excimer laser. The eyes were subdivided into three groups according to the preoperative refraction. The topographical data were imported into a custom software program that combined the Zernike high order terms having the same sign and angular frequency up to seventh order for 4-mm and 6-mm pupils, ie, coma and spherical aberrations, and midperipheral and peripheral high order aberrations. RESULTS: Photorefractive keratectomy induced a significant amount of the root-mean-square (RMS) values of the combinations of midperipheral and peripheral high order aberrations over the smaller pupil size for deeper myopic ablations (P<.05). Over the larger pupil, spherical myopic ablations showed a significant increase (P<.05) of the RMS values of coma and spherical aberrations. In the astigmatism group, the combination of terms having higher angular frequency increased significantly (P<.05) after surgery both over 4-mm and 6-mm pupils. CONCLUSIONS: After surface ablation, ablation depth and profile significantly influence the distribution and contribution of determined combinations of high order aberrations to the overall high order corneal wavefront aberration. Terms having high angular frequency were increased following large myopic correction and wide treatment zone. Quality of the whole corneal optics will be enhanced by designing future ablation profiles to compensate for peripheral high order optical aberrations.     

配戴角膜塑形镜后偏心对人眼高阶像差的动态影响

目的观察分析配戴角膜塑形镜后角膜光学压平区偏中心状态及不同瞳孔直径下人眼高阶像差的动态变化，探索偏心性质和程度对视觉的影响。方法前瞻性临床研究。30例年龄为（23．6-2．3）岁的中低度近视患者配戴夜戴型角膜塑形镜，等效球镜度为-0．75—．4．00D，平均（-2．61±0．83）D。在戴镜前和戴镜后1周、1个月、3个月分别检测角膜地形图，检测波前像差（在自然瞳孔下检查，分别提取3mm和6mm瞳孔直径下的全眼高阶像差结果），并通过分析戴镜后的角膜地形图形态，测量出角膜塑形镜压平区中心相对于瞳孔中心的偏心量（包括偏心距离和角度），只取右眼数据进行研究。采用Pearson相关性分析、重复测量资料方差分析对数据进行分析。结果配戴角膜塑形镜后1周、1个月、3个月时的平均偏心距离分别为（0．53±0．26）mm、（0．54±0．32）mm和（0．60±0．35）mm，偏心的方向主要集中于颞上方，偏心距离和角度在戴后3个时间点之间差异无统计学意义：戴后各时间点，偏心距离与戴前等效球镜度、初始散光量均不相关。在3mm与6mm瞳孔直径下，总高阶像差、总三阶像差、总四阶像差、总彗差（包括垂直彗差和水平彗差）、总三叶草和球差均方根值在戴后1周、1个月、3个月时均比戴前有明显增加，但各项像差在戴后各时间点之间差异均无统计学意义：在戴后的各个时间点，6mm瞳孔直径的像差结果都较3mm时大。戴后不同瞳孑L直径下，垂直或水平偏心距离与相应方向彗差在戴后各时间点均呈正相关；而总偏心距离与总高阶像差、总三阶像差、总四阶像差、总彗差、总三叶草和球差在戴后各时间点均不相关。结论配戴角膜塑形镜后偏心客观存在，程度较小并在1周后稳定；术后偏心会造成人眼高阶像差显著增加。     

Corneal higher order wavefront aberrations after hyperopic laser in situ keratomileusis

PURPOSE: To evaluate the changes in corneal higher order wavefront aberrations after hyperopic laser in situ keratomileusis (LASIK). METHODS: In a prospective case series, 15 eyes of 12 patients who had hyperopic LASIK were evaluated. Corneal topography was obtained before and after hyperopic LASIK with a Nidek EC 5000 laser using 5.5/8.0 ablation zones. Using anterior corneal height data, the changes in corneal higher order wavefront aberrations were calculated. RESULTS: The surgery significantly increased both corneal coma-like aberration (preoperative/6 months postoperative, 0.054/0.147 [172% increase] for 3-mm pupil and 0.381/1.076 [182% increase] for 6-mm pupil) and corneal spherical-like aberration (preoperative/6 months postoperative, 0.039/0.067 [72% increase] for 3-mm pupil and 0.297/0.959 [223% increase] for 6-mm pupil). The surgery significantly decreased Zernike coefficient 12 and the polarity of corneal spherical aberration changed from preoperative positive value to negative postoperatively. For a 3-mm pupil, the achieved changes in spherical equivalent refraction significantly correlated with the induced changes in the corneal coma-like aberration (R = 0.629, P = .010), but not with those in corneal spherical-like aberration (R = 0.408, P=.133) or Zernike coefficient 12 (R = -0.301, P = .282). For a 6-mm pupil, the achieved changes in spherical equivalent refraction significantly correlated with the induced changes in the corneal spherical-like aberration (R = 0.862, P < .0001) and Zemike coefficient 12 (R = -0.872, P < .001) but not with those in corneal coma-like aberration (R = 0.449, P = .094). CONCLUSIONS: Hyperopic LASIK significantly increases corneal coma-like and spherical-like aberrations and changes corneal spherical aberration from a positive to negative value.     

角膜屈光手术对眼波前像差的影响

目的　探讨大光斑式切削屈光手术对眼波前像差的影响 ,观察不同瞳孔区眼波前像差的改变。方法　检查 4 5例准分子激光原位角膜磨镶术 (laserinsitukeratomileusis,LASIK)患者术前、术后 10d和术后 1个月的裸眼视力 (uncorrectedvisualacuity ,UCVA)、最佳矫正视力 (bestcorrectedvisualacuity,BCVA)、等效球镜度 (sphericalequivalent,SE)及波前像差 ,根据术前SE将患者分为高度、中度和低度 3个不同的屈光度数组。使用Allegretto客观式波前像差分析仪检查眼部的波前像差 ,将所得数据进行统计学处理。结果　术前平均BCVA为 4 98± 0 0 7;术后 10d平均UCVA为 4 92± 0 10 ,BCVA为 4 95± 0 0 9;术后 1个月时平均UCVA为 4 96± 0 0 9,BCVA为 4 99± 0 0 9。视力在术后随时间延长而好转 ,术后 1个月时 2 6只眼 (30 6 % )BCVA好于术前。术后 10d各组的SE为轻度远视或正视状态 ,随时间延长向近视方向漂移。各屈光度数组内 ,术后 10d与 1个月时 ,高阶像差为术前的 2倍以上 ,以 5阶二次彗差为最 (P <0 0 5 ) ;术后 1个月 ,高阶像差比术后 10d有减小 (P >0 0 5 ) ,但未恢复至术前水平。总像差术后较术前减小。各组内 ,无论术前术后 ,瞳孔直径为 6 5mm时的像差显著大于瞳孔直径为 4mm时的像差 (P <0     

Regression and epithelial hyperplasia after myopic photorefractive keratectomy in a human cornea.

We present the histology of a cornea of a woman who had excimer laser photorefractive keratectomy (PRK) for myopia 6 months before she died in an accident. Preoperative spherical refraction was -6.00 diopters (D) with an astigmatism of -0.50 D. Six months postoperatively, refraction was -4.50 D. Slight corneal haze was noted at 1 and 3 months. The corneal histology showed marked epithelial hyperplasia in the center of the ablation zone without subepithelial deposition of newly synthesized collagen, proteoglycans, or both. The epithelial thickness was 38 microns in the untreated area and 93 microns in the center of the ablation. In conclusion, postoperative epithelial hyperplasia was responsible for regression after PRK in this eye.     

Effect of beam size on the expected benefit of customized laser refractive surgery

PURPOSE: Customized laser surgery attempts to correct higher order aberrations, as well as defocus and astigmatism. The success of such a procedure depends on using a laser beam that is small enough to produce fine ablation profiles needed to correct higher order aberrations. METHODS: Wave aberrations were obtained from a population of 109 normal eyes and 4 keratoconic eyes using a Shack-Hartmann wavefront sensor. We considered a theoretical customized ablation in each eye, performed with beams of 0.5, 1.0, 1.5, and 2.0 mm in diameter. We then calculated the residual aberrations remaining in the eye for the different beam sizes. Retinal image quality was estimated by means of the modulation transfer function (MTF), computed from the residual aberrations. Fourier analysis was used to study spatial filtering of each beam size. RESULTS: The laser beam acts like a spatial filter, smoothing the finest features in the ablation profile. The quality of the correction declines steadily when the beam size increases. A beam of 2 mm is capable of correcting defocus and astigmatism. Beam diameters of 1 mm or less may effectively correct aberrations up to fifth order. CONCLUSION: Large diameter laser beams decrease the ability to correct higher order aberrations. A top-hat laser beam of 1 mm (Gaussian with FWHM of 0.76 mm) is small enough to produce a customized ablation for typical human eyes.     

Induced optical aberrations following formation of a laser in situ keratomileusis flap

PURPOSE: To determine how refractive error, visual acuity, and high-order aberrations (3rd- and 4th-order) are affected by the formation of a lamellar corneal flap during laser in situ keratomileusis (LASIK). SETTING: University refractive surgery center. METHODS: The effect of lamellar corneal flap formation was analyzed in 15 myopic eyes (mean preoperative refraction -4.72 diopters [D] [range -1.25 to -7.25 D]). The flap was created using a 2-step procedure: (1). a nasally hinged lamellar corneal flap was created; (2). the flap was lifted and stromal ablation performed 2 months after the flap was made. A Hartmann-Shack aberrometer was used to measure the aberrations. RESULTS: There was no significant change in the refractive error (spherical equivalent pre-flap -4.72 +/- 1.99 D and post-flap -4.62 +/- 1.99 D [P =.28]) or visual acuity (pre-flap uncorrected visual acuity [UCVA] 0.07 and best corrected visual acuity [BCVA] 0.96; post-flap UCVA 0.08 and BCVA 0.95 [P =.16 and P =.33, respectively]). A statistically significant increase in total higher-order wavefront aberrations was observed following flap formation (root mean square pre-flap 0.344 +/- 0.125 and post-flap 0.440 +/- 0.221 [P =.04]). CONCLUSION: Flap formation during LASIK can modify the eye's existing natural higher-order aberrations (especially spherical and coma-like aberrations along the axis of the flap's hinge), while visual acuity and refractive error remain unaffected.     

Aberration-sensing and wavefront-guided laser in situ keratomileusis: management of decentered ablation

PURPOSE: To clarify the feasibility of aberration-sensing and wavefront-guided laser in situ keratomileusis (LASIK) to manage grossly decentered ablation and to discuss the limitations of the technology. METHODS: Three patients with previous decentrations of the ablation zone between 1.5 to 2.0 mm were scheduled for wavefront-guided LASIK. All patients reported monocular diplopia and halos. Wavefront aberrations were measured with a Tscherning-type aberrometer. Laser ablation was done with a WaveLight Allegretto in a one-step procedure with ablation profiles calculated only from the individual wavefront map. Decentrations were determined from corneal topography. RESULTS: Three months after surgery, patient WM and patient SU had gained uncorrected and best spectacle-corrected visual acuity. The root mean square-wavefront error decreased up to 61% and 33%, respectively, for total and higher order aberrations (Zernike modes of 3rd order and higher). There was significant enlargement of the optical zone determined by corneal topography, and both patients no longer reported diplopia and halos at 3 months postoperatively. The optical aberration of the third patient (RE), after a 5.00-D overcorrection with a 2-mm decentration, was too high for aberration-sensing; retinal images obtained from the wavefront device were too smeared and not of sufficient contrast. In addition, this patient had a residual corneal thickness of 416 microm and thus wavefront-guided LASIK was not done. CONCLUSIONS: Wavefront-guided LASIK offers a new way of managing grossly decentered laser ablations. Unfortunately, there are still patients who have aberrations too large for wavefront sensing or with other clinical limitations such as a residual corneal thickness too thin for further treatment.     

Prospective randomized study of corneal aberrations 1 year after radial keratotomy or photorefractive keratectomy

PURPOSE: To evaluate the optical properties of the cornea 1 year after either radial keratotomy (RK) or photorefractive keratectomy (PRK) in a randomized group of patients with low myopia. METHODS: Ninety-six patients with myopia between -0.75 and -5.00 D were randomized to either radial keratotomy (n = 46) or photorefractive keratectomy (n = 50). Topography maps were obtained 1 year after surgery and analyzed by computation of total corneal wavefront aberration and Zernike polynomial coefficients for pupil sizes of 2, 4, and 6 mm. The 4-mm pupil size was used for optimization of the model. RESULTS: The total corneal wavefront aberrations after RK and PRK were similar and not statistically different. Wavefront aberrations arising from astigmatism or defocus accounted for approximately 70% of the total wavefront error at all pupil sizes in both groups. All types of aberrations, and in particular spherical aberration, increased significantly with increasing pupil size. Higher-order wavefront aberrations were almost twice as high after RK than after PRK at pupil sizes of 4 and 6 mm. Spherical aberration and coma were slightly higher after PRK than after RK. CONCLUSIONS: Pupil size had a major effect on corneal aberrations after RK and PRK. The most important aberrations were sphero-cylindrical, in which eyes became significantly more myopic with increasing pupil size. The image forming properties of the cornea are better after PRK compared with RK due to the lesser amount of higher-order aberrations.     

Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis

OBJECTIVE: To assess the relation between magnitude of refractive correction and changes in higher order wavefront aberrations of the cornea after laser in situ keratomileusis. DESIGN: Prospective, consecutive, nonrandomized comparative trial (self-controlled). PARTICIPANTS: One hundred eyes of 53 patients with myopia (-2.0 to -13.0 diopters) were included. INTERVENTION: Laser in situ keratomileusis was performed. Videokeratography measurements were conducted before and 1 month after surgery. MAIN OUTCOME MEASURES: The videokeratography data were used to calculate the higher order wavefront aberrations of the cornea for both small (3 mm) and large (6 mm) pupils. RESULTS: For a 3-mm pupil, the surgery significantly increased coma-like (2.4 +/- 1.3-fold, P < 0.001, paired t test) and spherical-like (1.8 +/- 0.9-fold, P < 0.001) aberrations. For a 6-mm pupil, both coma-like (4.4 +/- 3.3-fold, P < 0.001) and spherical-like (9.4 +/- 5.2-fold, P < 0.001) aberrations were significantly increased by surgery. The amount of achieved correction showed significant correlations with the changes in coma-like (Pearson correlation coefficient r = 0.446, P < 0.001) and spherical-like (r = 0.348, P < 0.001) aberrations for a 3-mm pupil, and coma-like (r = 0.566, P < 0.001) and spherical-like (r = 0.693, P < 0.001) aberrations for a 6-mm pupil. The eyes that lost 2 or more lines of baseline spectacle-corrected visual acuity showed significantly larger induced increases in coma-like (P = 0.003, Mann-Whitney U test) and spherical-like (P = 0.009) aberrations for a 3-mm pupil than those that either improved or remained within 1 line of spectacle-corrected visual acuity CONCLUSIONS: Laser in situ keratomileusis, performed using the current algorithms, increases higher order wavefront aberrations of the cornea, dependent on the amount of refractive correction.     

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.     

角膜瓣上行准分子激光切削治疗LASIK术后屈光回退的临床研究

目的观察在角膜瓣上使用不同光区进行准分子激光切削治疗准分子激光原位角膜磨镶术（LASIK）术后屈光回退的视力变化及像差差异,研究对一些LASIK术后屈光回退而角膜已不足够厚的病例,进行切实可行的手术方案。方法 LASIK术后屈光回退的病例48例（84只眼）,因残余角膜薄而不能在角膜基质床行增强治疗,将84只眼分5组,在角膜瓣上分别使用4.5 mm、5.0 mm、5.5 mm、6.0 mm、6.5 mm的光区进行激光切削,对各组术后10 d1、个月3、个月6、个月的视力情况以及术后6个月的像差变化结果进行分析。结果各光区组术后短期内（1个月以内）裸眼视力均可达到术前最佳矫正视力（P〉0.05）,但4.5 mm、5.0 mm5、.5 mm的光区组术后3个月视力有不同程度的回退,而6.0 mm6、.5 mm光区组视力稳定;术后6个月各组的球差均较术前增大,而5.5 mm以下组像差增加又明显高于6.0 mm以上组（P〈0.05）。结论在角膜瓣上行准分子激光切削在一定程度上可解决LASIK术后屈光回退而角膜薄的问题,但其应用也有一定范围,在角膜瓣上进行切削最好使用6.0mm以上光区,这样才能有效地避免术后屈光再回退及高阶像差增加的问题。