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Comparison of the flaps made by femtosecond laser and automated keratomes for sub-bowman keratomileusis ZHAI Chang-bin1*, TIAN Lei1*, ZHOU Yue-hua1, ZHANG Qing-wei1 and ZHANG Jing1 1 Ophthalmic Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology & Visual Sciences Key Lab, Beijing 100730, China. No author has a financial or proprietary interest in any material or method mentioned. Correspondence to: Dr. ZHOU Yue-hua, Ophthalmic Center, Beijing Tongren Hospital, No. 1 Dongjiaomin Ln, Dongchong District, Beijing 100730, China. Phone: +8613910836019 Fax: +861058269072 Email: [email protected] * The first two authors contribute equally to this article. Background: To assess and compare the variations of LASIK flap created by the IntraLase femtosecond laser, Moria One Use-Plus SBK and Moria M2 Single-Use 90 µm-head microkeratome using Anterior segment optical coherence tomography (Visante® OCT). Methods: 161 eyes of 81 consecutive patients were enrolled in this prospective study and randomized divided into three groups depending on the flap creation method: flap creation with the the IntraLase femtosecond laser (IntraLase group, 59 eyes), with the Moria One Use-Plus SBK (SBK group , 44 eyes) and with the Moria M2 Single-Use 90 µm-head microkeratome (M2SU90 group, 58 eyes). Nominal flap thickness was 110 μm for all patients and for the three devices. One month after surgery, Visante® OCT was used to measure flap thickness at 20 locations on each cornea and the results were assessed for uniformity, regularity and accuracy. Results: At one month after surgery, the mean central flap thickness was 111.18±3.33 µm in the IntraLase group, 113.85±8.07 µm in the SBK group and 117.96±13.14 µm in the M2SU90 group, respectively. The flaps in the IntraLase group and the SBK group were more regular, showing an almost planar configuration, than the meniscus-shaped flaps in the M2SU90 group. The maximum deviation from the intended flap thickness (110 µm) was 6.15 µm in the IntraLase group, 10.36 µm in the SBK group and 19.75 µm in the M2SU90 group, respectively. A differences greater than 20 µm was observed in 0.42% of measurements in the IntraLase group; 2.95% of measurements in the SBK group and 21.12% of measurements in the M2SU90 group. Conclusions: The flaps created by the IntraLase femtosecond laser and Moria One Use-Plus SBK are more uniform; more regular and more accurate than those created by the Moria M2 Single-Use 90 µm-head microkeratome. The first two methods can make precise flaps for Sub-Bowman Keratomileusis. Keywords: sub-bowman; keratomileusis; femtosecond laser ; microkeratome; flap thickness; Corneal ectasia is one of the most serious complications of Laser in situ keratomileusis (LASIK). Sufficient residual stromal bed (RSB) thickness (exceeding 250 µm) is important to reduce the likelihood of corneal ectasia. Sub-Bowman Keratomileusis is a LASIK procedure in which the flap is thinner (thin-flap LASIK) with a planar flap architecture 1. A major advantage of creating a thin flap during Sub-Bowman Keratomileusis is leaving sufficient stromal tissue to allow safer excimer laser ablation in patients with moderate or high myopia. Several years ago, doctors advocated that the ideal flap thickness in LASIK should exceed 130 µm because thin flaps may be associated with a higher frequency of potential complications, such as flap folds, striae, epithelial ingrowth, and irregular astigmatism2. But more recent report advocates performing Sub-Bowman Keratomileusis with flaps ranging from 90 µm to 110 µm in thickness3. Some reports showed that thin flaps were associated with better early visual and refractive results than thick flaps4. There are three methods to achieve a thin flap in the most clinical center. The traditional one is using Moria M2 microkeratome with plastic single use 90 µm-head; the second method is using Moria One Use-Plus microkeratome with SBK head and the most recent one: Femtosecond laser, which uses ultrafast pulses of energy to induce photo-disruption of tissue with minimal collateral tissue damage and inflammation at a preset depth. The purpose of this study was to compare the thickness and uniform, regularity and accuracy of the flaps using anterior segment optical coherence tomography (Visante® OCT). In this study, we assessed and compared the configuration of LASIK flap created by the IntraLase FS60 laser (Abbott Medical Optics, Santa Ana, California, USA) and the Moria One Use-Plus microkeratome with SBK head (Moria, Antony, France) and the Moria M2 microkeratome with single use 90 µm-head (Moria, Antony, France). METHODS Patients One hundred and sixty-one eyes of eighty-one consecutive patients who were scheduled bilateral LASIK treatment from December 2011 to August 2012 in the Tongren Ophthalmic Center of Capital Medical University (Beijing, China) enrolled in this prospective study. Patients with ocular pathologies such as corneal scars, corneal dystrophies, previous ocular surgery, keratoconus, glaucoma, diabetes, and systemic diseases known to affect eyes were excluded. All the patients were told about characteristics and indications about the three different methods for creating corneal flaps particularly, they freely chose one from these three surgical procedures. The first group had flaps with the IntraLase femtosecond laser (IntraLase group). The second group made the flaps with the Moria One Use-Plus microkeratome with SBK head (SBK group); the third group used Moria M2 microkeratome with plastic single used 90 µm-head (M2SU90 group) for flap creation. This study was a prospective, randomized, comparative clinical study. All patients signed an informed consent in accordance with the tenets of the Declaration of Helsinki. Surgical Procedure Preoperative examination included the following standard measurements: cornea thickness by ultrasound pachymetry, corneal topography, silt-lamp biomicroscopy, uncorrected visual acuity (UCVA), best corrected visual acuity (BSCVA), intraocular tension measurement (NCT), applanation tonometry, fundus examination, manifest refraction and cycloplegic refraction. All surgeries were performed by the same surgeon (Y.H.Z.) under topical anesthesia. The corneal flaps were created using the IntraLase FS60 laser or the Automated Keratome. After lifting the flap, ablation was performed using the Visx S4 excimer laser (VISX Inc., Santa Clara, USA). The corneal flap and stroma surface were irrigated with balanced normal saline solution, and the flap was replaced. Postoperative, patients were instructed to use 0.1%fluorometholone four times per day for 3 days, and then tapered over for two weeks, levofloxacin eye drops and artificial tears four times per day for 2 weeks. All patients were asked to have regular follow-up visits. IntraLase Femtosecond laser. In order to obtain a flap thickness of 110 μm, the IntraLase femtosecond laser with the 60 kHz laser engine was programmed to a thickness of 110 μm. The other settings were: 8.5 mm diameter, side-cut energy of 0.08 μJ, side-cut angle of 70º, raster pattern energy of 0.75 μJ, spacing between each laser spot and raster line of 8x8 μm, a superior hinge with hinge angle of 45° and the pocket enabled. One Use-Plus SBK microkeratome. The Moria One Use-Plus microkeratome with SBK head was used to create an 8.5-9.0 mm diameter corneal flap with a nasal hinge. This device is used to obtain an attempted central flap thickness of 110 μm with a calibrated 90 µm-head selecting the lowest speed (“Speed 1”) on the associated Evolution 3 control unit. M2 Single-Use 90 µm-head microkeratome. The Moria M2 microkeratome with a plastic single use 90 µm-head was used to create an 8.5-9.0 mm diameter corneal flap with a superior hinge. The calibrated 90 µm-head is a plastic, single used device. It is used to obtain a central flap thickness of 110 µm selecting the lowest speed (“Speed 1”) on the associated Evolution 3 control unit. Anterior Segment Optical Coherence Tomography Technology The Visante® OCT (Carl Zeiss Meditec, Inc.) is a computerized instrument that acquires and analyzes cross-sectional tomograms of the anterior eye segment (cornea, anterior chamber, iris and the central portion of the lens). It employs non-invasive, non-contact, low-coherence interferometry to obtain these high-resolution images. We can obtain cross-sectional tomograms of the cornea at any appointed meridians using this device (Figure 1). In our study, the 0°,45°,90°and 135°meridians OCT images were acquired by the same skilled technician at one month after surgery (Figure 2A). In the cross-sectional images, the LASIK flap was clearly visible by increased reflection at the flap interface and increased internal reflectivity5. Then, the flap thickness was measured using the semi-manual software’s flap tool by the same technician who did not know the designed flap dimension. Flap thickness was measured at 5 points in each meridian obtained for each eye (for a total of 20 measurements for each eye in the study). For each meridian, 1 location was at the central zone (between ±0.5 mm from the flap vertex); 2 locations were at the paracentral zone (±1 to 2 mm from the flap vertex); 2 locations were at the peripheral zone (±3 to 5 mm from the flap vertex) (Figure 2B). Statistical analysis Data were expressed as mean ± standard deviation (SD) and analyzed with SPSS 17.0 software (SPSS Inc, Chicago, Illinois). An Independent-samples t test and one-way analysis of variance (ANOVA) were used to analyze measurement data conforming to normal distribution and a Wilcoxon signed ranks test was applied for measurement data not conforming to normal distribution. A P value < 0.05 was considered statistically significant. RESULTS Preoperative Characteristics The preoperative characteristics of the patients are shown in Table 1. No significant differences were observed among the three groups (P>0.05). Central Flap Thickness The mean central flap thickness at one month postoperative were 111.18±3.33 µm (range: 103.75 to 119.50 µm) in the IntraLase group, 113.85±8.07 µm (range: 97.50 to 130.00 µm) in the SBK group and 117.96±13.14 µm (range: 93.50 to 156.00 µm) in the M2SU90 group. The distribution of central flap thickness for all eyes were presented in Figure 3. Flap Thickness Uniformity Table 2 shows the mean standard deviation of the flap thickness measurements at each of the 20 locations measured in each eye for the three groups. The IntraLase flaps and the SBK flaps were more uniform, showing an almost-planar configuration. The maximum deviations were 7.73 µm in the IntraLase group and 12.78 µm in the SBK group, among the 20 different measurements of each flap. The flaps created with the M2SU90 Keratome were thinner in the central zone and thicker in the periphery, which provided a meniscus shape, with the maximum deviation of 19.42 µm. Flap Thickness Regularity The IntraLase flaps and the SBK flaps were more regular than the M2SU90 flaps when measured from the center to the periphery. The average thickness values in the central, paracentral and peripheral zones were not significantly different in the IntraLase group (111.17±3.33 µm,111.10±2.85 µm and 110.34±3.42 µm, respectively. P>0.05, by ANOVA) and the SBK group(113.85±8.07 µm,111.89±5.17 µm and 113.78±4.79 µm, respectively. P>0.05, by ANOVA). In the M2SU90 group, the central flap thickness was statistically significantly thinner than the peripheral zones with the mean flap thickness of 117.96±13.14 µm , 117.01±13.43 µm and 123.11±13.77 µm, respectively (P<0.05, by ANOVA). Flap Thickness Accuracy The mean deviation between the achieved and attempted flap thickness were smaller in the IntraLase group and the SBK group than in the Moria M2SU90 group. The IntraLase flap maximum deviation from the intended 110 µm of the 20 measurements was 6.15 µm. The SBK group was 10.36 µm, whereas the M2SU90 group from the intended 110 µm was 19.76 µm (Table 3). Figure 4 shows the distributions of the differences between the intended corneal flap thickness and the measured flap thickness in the IntraLase group (59 eyes, 1180 measurements), the SBK group (44 eyes, 880 measurements) and in the M2SU90 group (58 eyes, 1160 measurements). The differences were less than 5 µm in 682 measurements (57.79%) in the IntraLase group; in 363 measurements (41.25%) in the SBK group and in 271 measurements (20.17%) in the M2SU90 group. Differences greater than 20 µm were observed in 5 measurements (0.42%) in the IntraLase group; in 26 measurements (2.95%) in the SBK group and in 303 measurements (21.12%) in the M2SU90 group one month after surgery. DISCUSSION Thin flap LASIK (Sub-Bowman keratomileusis) is a safe technique to correct myopic defects. Moreover, it achieves excellent refractive outcomes, a lower rate of enhancements, and a good visual performance with better contrast sensitivity6. Precise creation of the corneal flap is essential for successful Sub-Bowman keratomileusis. With the improvement in traditional mechanical microkeratome system and the development of the femtosecond laser, it is now possible to achieve clinically uniform flaps in LASIK7. Femtosecond laser tend to create a planar flap with highly predictable thickness and diameter. Stahl et al.8 demonstrated that a femtosecond laser created a uniform flap with minimal variability, which made the process of creating a thin LASIK flap safer and accurate.Main et al. 9 demonstrated that LASIK flaps created with a femtosecond laser provide better astigmatic neutrality, induction of fewer higher-order aberrations and decreased epithelial injury compared to traditional mechanical microkeratomes. In treating myopic refractive errors, the laser ablation is deepest in the central cornea, which is also the area of the cornea that is thinnest. Most flap research is mainly focused on this central portion of the flap and stromal bed10. However, decreased post-operative visual performance such as glare and halo under dim conditions, poor night vision and decreased contrast sensitivity values have been reported and may be related to more peripheral corneal distortions11. Therefore, analysis of central corneal parameters alone in LASIK may be less than optimal. Fortunately, research on flap morphology and its effects on postoperative flap performance have gained more attention in recent years. In this study, we acquired thickness measurements at 20 points in the 0°,45°,90°and 135°meridians in each eye by Visante® OCT and divided these points into the central, paracentral and peripheral zones. Traditionally, ultrasound pachymetry has been used to measure corneal flap and stromal bed thickness, but this technique has many potential pitfalls including the risk of damage of the corneal epithelium, creating localized variations in corneal bed hydration which could affect the laser ablation, and the risk of infection transmission with the ultrasound probe. Furthermore, it is difficult to exactly correlate the position of the pre- and intra-operative measurements, and it is very difficult to describe flap thickness throughout the entirety of the flap12,13. Using the non-invasive, non-contact Visante® OCT, we can obtain the high-resolution images of the cornea at any appointed meridians, and can therefore precisely measure the flap thickness at any points14. Kim et al.15 also reported that Visante® OCT is more reliable than ultrasound pachymetry in measuring the central corneal flap thickness. Our data revealed that the IntraLase flaps and the SBK flaps have more uniform and regularity thickness than the M2SU90 flaps. In the M2SU90 group, the central flap thickness was thinner than the paracentral and peripheral flap thickness (P<0.05). Some clinical trials also revealed the differences16. The reason why Moria One Use-Plus SBK can make a uniform thickness flap compared with Moria M2 Single-Use 90 μm-head may be because the working mechanisms are different. The Moria M2 Single-Use 90 μm-head microkeratome has a hinge in the superior and the One Use-Plus SBK gets a hinge at the nasal. Another possible reason may be that the 90 μm distance on the plastic head is not accurate. The accuracy of the LASIK flap thickness is a key factor in security. In order to maintain postoperative corneal strength, and prevent that corneal flap become thinner, especially avoid the occurrence of iatrogenic keratoconus, the residual stromal thickness must be more than 250 μm17. The residual stromal thickness was calculated with the preoperative corneal thickness minus the prediction flap thickness and the laser ablation flap thickness. If the difference between the attempted thickness and achieved thickness is too large, patients will be greatly in danger, especially for those with too-thin corneal thickness. In our trial, the IntraLase flap maximum deviation from the intended 110 µm was 6.15 µm, the SBK was 10.36 µm and the M2SU90 maximum deviation from the intended 110 µm was 19.75 µm. The maximum deviations in the three groups were produced in the peripheral zone, and in this region, the accuracy of femtosecond laser group was better than the SBK group and the M2SU90 group (Table 3). It is reported that the corneal flap could affect low-level aberrations18, and increase the higher-order aberrations19. These factors caused a negative impact to the postoperative visual quality. Durrrie et al.20 reported that in 51 consecutive patients, one eye was randomized to have the flap created with the IntraLase femtosecond laser and the other flap using a standard microkeratome. The result showed that there was significantly less astigmatism and trefoil in the IntraLase group. Under these conditions that people pursuit higher visual quality, an uniform thin corneal flap with high predictability and regularity attracted more and more attention. The SBK flaps created by the femtosecond laser are safer, more accurate and have better visual quality. It should be first choice for patients. But in some clinic without femtosecond laser, Moria One Use-Plus SBK can also get a predictable uniform flap. REFERENCES 1. Kermani O, Fabian W, Lubatschowski H. Real-time optical coherence tomography-guided femtosecond laser sub-Bowman keratomileusis on human donor eyes. Am J Ophthalmol 2008; 146: 42-45. PMID: 18439562 2. Steinert RF, Ashrafzadeh A, Hersh PS. Results of phototherapeutic keratectomy in the management of flap striae after LASIK. Ophthalmology 2004; 111: 740–746. PMID: 15051207 3. Durrie DS, Slade SG, Marshall J. Wavefront-guided excimer laser ablation using photorefractive keratectomy and sub-Bowman's keratomileusis: a contralateral eye study. J Refract Surg 2008; 24: S77-84. PMID: 18269155 4. Eleftheriadis H, Prandi B, Diaz-Rato A, Morcillo M, Sabater JB. The effect of flap thickness on the visual and refractive outcome of myopic laser in situ keratomileusis. Eye 2005; 19: 1290-1296. PMID: 15618975 5. Li Y, Netto MV, Shekhar R, Krueger RR, Huang D. A longitudinal study of LASIK flap and stromal thickness with high-speed optical coherence tomography. Ophthalmology 2007; 114: 1124-1132. PMID: 17320959 6. Cobo-Soriano R, Calve MA, Beltran J, Llovet FL, Baviera J. Thin flap laser in situ keratomileusis: analysis of contrast sensitivity, visual, and refractive outcomes. J Cataract Refract Surg 2005; 31: 1357-1365. PMID: 16105607 7. Zhou YH, Tian L, Wang N, Dougherty PJ. Anterior segment optical coherence tomography measurement of Lasik flaps: femtosecond laser vs microkeratome. J Refract Surg 2011; 27(6): 408-416. PMID: 21117541 8. Stahl JE, Durrie DS, Schwendeman FJ, Boghossian AJ. Anterior segment OCT analysis of thin IntraLase femtosecond flaps. J Refract Surg 2007; 23: 555-558. PMID: 17598572 9. Mian SI, Li AY, Dutta S, Musch DC, Shtein RM. Dry eyes and corneal sensation after laser in situ keratomileusis with femtosecond laser flap creation Effect of hinge position, hinge angle, and flap thickness. J Cataract Refract Surg 2009; 35: 2092-2098. PMID: 19969213 10. Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton H, Coleman DJ. Probability model of the inaccuracy of residual stromal thickness prediction to reduce the risk of ectasia after LASIK part II: quantifying population risk. J Refract Surg 2006; 22: 861-870. PMID: 17124880 11. Von JB, Kohner T. Corneal architecture of femtosecond laser and microkeratome flaps imaged by anterior segment optical coherence tomography. J Cataract Refract Surg 2009; 35:35-41. PMID: 19101422 12. Flanagan GW, Binder PS. Precision of flap measurements for laser in situ keratomileusis in 4428 eyes. J Refract Surg 2003; 19: 113-123. PMID: 12701715 13. Eisner RA, Binder PS. Technique for measuring laser in situ keratomileusis flap thickness using the IntraLase laser. J Cataract Refract Surg 2006; 32: 556-558. PMID: 16698470 14. Lazaro C, Hernandez EM, Martinez D, Redondo P. Comparison of central corneal thickness measured with anterior segment optical coherence tomography versus ultrasonic pachymetry. Arch Soc Esp Oftalmol 2013; 88: 45-49. PMID: 23433191 15. Kim JH, Lee D, Rhee KI. Flap thickness reproducibility in laser in situ keratomileusis with a femtosecond laser: optical coherence tomography measurement. J Cataract Refract Surg 2008; 34: 132-136. PMID: 18165093 16. Alio JL,Pinero DP. Very high-frequency digital ultrasound measurement of the LASIK flap thickness profile using the IntraLase femtosecond laser and M2 and Carriazo-Pendular microkeratomes. J Refract Surg 2008; 24: 12-23. PMID: 18269144 17. Sugar A, Rapuano CJ, Culbertson WW, Huang D, Varley GA, Aqapitos PJ, et al. Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy: a report by the American Academy of Ophthalmology. Ophthalmology 2002; 109: 175187. PMID: 11772601 18. Porter J, MacRae S, Yoon G, Robert C, Cox IG, Williams DR. Separate effects of the microkeratome incision and laser ablation on the eye's wave aberration. Am J Ophthalmol 2003; 136: 327-337. PMID: 12888057 19. Wang Y, Zhao KX, He JC;Jin Y, Zuo T. Ocular higher-order aberrations features analysis after corneal refractive surgery. Chin Med J (Engl) 2007; 120: 269-273. PMID: 17374275 20. Durrie DS, Kezirian GM. Femtosecond laser versus mechanical keratome flaps in wavefront-guided laser in situ keratomileusis: prospective contralateral eye study. J Cataract Refract Surg 2005; 31: 120-126. PMID: 15721704 Figure 1. Example of 0° meridian cross-sectional. Visante® OCT image of the cornea. Figure 2A. The 0°, 45°, 90°, and 135° meridians of the cornea. Figure 2B. The five points in each meridian. From the corneal vertex, the “+” is in the positive X-axis and “-” is in the negative X-axis direction of the image. Figure 3. Distribution of mean central flap thicknesses at 1 month post-surgery for all eyes made with IntraLase femtosecond laser; Moria One Use-Plus SBK and Moria M2SU90 Mechanical Keratome. Figure 4. Distribution of the differenc in flap thickness among the IntraLase group, the SBK group and the M2SU90 group. Table1. Preoperative characteristics of patients. Parameter IntraLase FS Moria OUP SBK Moria M2SU90 No. of eyes 59 44 58 P Value Age(y) Mean±SD Range 27.00±4.96 28.1±6.98 25.5±4.89 18 to 44 21 to 40 19 to 36 -7.15±2.87 -7.88±3.24 0.3725 SER (D) Mean±SD Range -9.20±3.97 -11 to -3 -11.63 to -3.63 -13.88 to -3.63 514.24±34.56 519.50±22.89 506.83±26.78 0.0975 CCT (µm) Mean±SD 0.4824 Range 442 to 603 474 to 602 470 to 550 44.29±1.82 43.68±0.89 43.79±1.73 39.72 to 47.98 41.79 to 46.61 40.45 to 46.82 Corneal curvature(D) Mean±SD Range 0.4458 SER=spherical equivalent refraction; CCT= central corneal thickness Table 2. The mean flap thickness and standard deviation of the relevant 20 measurements in the four meridians among the IntraLase group, SBK and M2SU90 group. Flap Thickness (Mean±Standard Deviation) (µm) Measurement points -Peripheral -Paracentral meridian 109.66±7.37 111.20±4.82 45° meridian 110.00±7.69 90° meridian 135°meridian Central Paracentral Peripheral 110.49±5.90 110.64±5.91 108.42±7.54 110.22±5.17 112.78±6.68 113.69±5.45 109.93±6.37 110.75±7.26 110.54±6.39 109.58±6.30 110.39±7.22 110.53±6.50 112.05±7.73 110.85±6.02 111.86±6.36 111.29±5.93 111.42±6.89 114.77±9.69 109.59±10.48 112.22±9.97 111.61±8.06 111.77±7.53 45° meridian 113.73±11.52 109.82±8.47 114.70±8.97 110.86±9.40 113.39±9.19 90° meridian 116.02±9.07 114.48±8.04 114.93±12.64 11.95±8.47 115.45±6.73 135°meridian 110.00±8.47 112.39±8.92 113.55±12.78 112.43±8.51 115.14±8.27 meridian 125.17±20.39 120.45±14.08 116.60±14.98 115.62±16.82 120.72±16.90 45° meridian 126.64±18.15 118.03±16.82 118.86±14.12 114.76±14.71 120.81±19.42 90° meridian 124.53±16.94 116.57±13.33 118.71±16.11 116.45±15.68 120.40±18.06 135°meridian 125.53±15.94 115.66±16.29 117.69±15.72 118.56±15.11 126.64±18.06 IntraLase 0° SBK 0° meridian M2SU90 0° Table 3. The mean deviations from the intended flap thickness of the 20 corresponding measurements among the IntraLase flaps, One Use-Plus SBK and the M2 Sing-Use 90 µm -head Microkeratome flaps. Measurement points Mean±Standard Deviation Flap Thickness (µm) -Peripheral -Paracentral meridian 5.42±4.96 4.15±2.68 45° meridian 5.93±4.83 90° meridian 135°meridian Central Paracentral Peripheral 4.59±3.72 4.58±3.75 6.22±4.47 4.22±2.95 5.93±4.08 5.93±3.42 4.88±4.04 5.66±4.55 5.32±3.52 5.00±3.80 5.98 ±3.98 5.34±3.67 6.15±5.05 4.78±3.70 5.29±3.94 4.92±3.51 5.39±4.47 8.90±6.00 8.32±6.26 8.00±6.24 6.80±4.51 6.09±4.69 45° meridian 10.36±6.09 6.59±5.23 8.70±5.06 6.86±6.40 7.84±5.77 90° meridian 8.75±6.41 7.16±5.71 10.11±8.95 7.91±4.87 7.00±5.06 135°meridian 7.14±4.43 7.39±5.44 8.64±9.99 6.70±5.70 7.55±6.09 meridian 19.76 ±15.90 14.13±10.30 12.60±10.36 13.31±11.61 15.34±12.76 45° meridian 19.36±15.15 15.00±10.99 12.24±11.26 11.93±9.73 17.36±13.76 90° meridian 17.74±13.48 11.50±9.34 13.57±12.22 13.52±10.11 15.91±13.36 135°meridian 17.91±13.16 13.62±10.44 12.83±11.82 13.71±10.57 18.33±15.27 IntraLase 0° SBK 0° meridian M2SU90 0°