Changes in the refractive index of the human corneal stroma during laser in situ keratomileusis. Effects of exposure time and method used to create the flap

PURPOSE: To compare the refractive index and calculated stromal bed hydration lifting the flap before and after photoablation during uneventful laser in situ keratomileusis (LASIK) using a microkeratome (M2, Moria) or a femtosecond laser (IntraLase, IntraLase Corp.) to create the flap. SETTING: Vissum-Instituto de Oftalmológico de Alicante, Alicante, Spain. METHODS: Uneventful LASIK was performed in 76 eyes of 49 patients. Flaps were created using a microkeratome (57 eyes) or a femtosecond laser (19 eyes). On lifting the flap, the refractive index of the stroma was measured using a customized manual Abbé refractometer. The measurement was repeated immediately after photoablation. Treatment time was noted. Hydration was calculated using the Fatt-Harris equation. RESULTS: Before LASIK, the mean refractive index was 1.366+/-0.0049 (SD) in the microkeratome group and 1.374+/-0.0047 in the femtosecond group. After LASIK, it was 1.382+/-0.0066 and 1.391+/-0.0102, respectively. The increase after ablation was statistically significant in both groups (P<.001). The increase in the refractive index linearly correlated with treatment time (microkeratome: r=0.355, P=.007; femtosecond, r=0.506, P=.027). Before photoablation, the refractive index was significantly lower in the microkeratome group than in the femtosecond group (P<.001). There was no significant difference in age between the 2 groups. CONCLUSIONS: Photoablation increased the refractive index of the stroma, and the increase was influenced by treatment time. Hydration of the stroma was 1.8 mgm/mgm greater in the microkeratome group than in the femtosecond laser group.     

Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront-guided laser in situ keratomileusis

PURPOSE: To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser. SETTING: Private practice refractive surgery center, Irvine, California, USA. METHODS: This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation. RESULTS: Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar. CONCLUSIONS: The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.     

飞秒激光和机械刀行LASIK术后角膜神经形态学特征的共焦显微镜观察

目的在共焦显微镜下观察飞秒激光和机械刀行准分子激光原位角膜磨镶术（LASIK）术后角膜神经的形态差异。方法近视眼患者34例（68只眼）,一组行飞秒激光下的LASIK（28只眼）,另一组行Moria-2机械刀下的LASIK（40只眼）,术后1个月、3个月对两组角膜在共焦显微镜下进行观察。结果术后各时期两组裸眼视力无显著性差异,术后1个月两组角膜瓣界面均可见高反光颗粒,未见完整神经纤维,术后3个月,飞秒激光组角膜神经完整性明显高于机械刀组（P〈0.01）。结论飞秒激光行LASIK术后角膜神经的修复快于机械刀。     

Biomechanical effects of femtosecond and microkeratome-based flap creation: prospective contralateral examination of two patients

PURPOSE: To examine flap morphology, corneal topography, and aberrometry after flap creation with a femtosecond laser in one eye and a mechanical microkeratome in the fellow eye. Comparative outcomes after subsequent refractive laser correction were also investigated. METHODS: Two patients (4 eyes) were enrolled in a clinical study in which LASIK flaps were created using the IntraLase laser set at 90 or 100 microm in one eye and the Moria M2 microkeratome with a 90-microm head in the fellow eye. Pre- and postoperative flap data at 1 day, 1 week, and 1 month were collected before lifting the flap to perform a customized laser ablation (Alcon LADARVision4000 CustomCornea System). Postoperative laser data were collected at 1 week, 1 month, 3 and 6 months, and 1 year. Visual acuity, pachymetry, high-frequency flap ultrasound profilometry (Artemis Ultralink), topography, aberrometry (LADARWave), and refraction were examined and compared between eyes. RESULTS: Postoperative flap comparisons showed a hyperopic refractive shift in all four eyes with a shift of up to 1.00 diopter (D) in the microkeratome eyes and < 0.50 D in the IntraLase eyes. Corneal topography difference maps showed peripheral steepening that was more pronounced in the microkeratome versus IntraLase eyes (2.00 D vs 0.50 to 1.00 D, respectively). Spherical aberration by wavefront variably increased by 50% to 100% in the microkeratome eyes and remained virtually unchanged in the IntraLase eyes. At 3-month postoperative laser treatment, visual acuity was 20/15 for both eyes in patient 1 and 20/15 in the right eye (IntraLase) and 20/25 in the left eye (microkeratome) in patient 2. Aberrometry revealed a two-fold greater level of higher order aberrations in microkeratome eyes than in IntraLase eyes throughout the postoperative laser period. CONCLUSIONS: Femtosecond laser and mechanical methods of flap creation lead to subtle biomechanically induced aberrations, which appear more prominent with the mechanical Moria M2 microkeratome in this small case study. Further study with a larger patient population is warranted to determine whether these differences are statistically significant.     

Femtosecond laser versus mechanical keratome flaps in wavefront-guided laser in situ keratomileusis: prospective contralateral eye study

PURPOSE: To compare the outcomes of wavefront-guided laser in situ keratomileusis (LASIK) performed using the IntraLase femtosecond laser with the outcomes using the Hansatome mechanical microkeratome. SETTING: Private clinic, Overland Park, Kansas, USA. METHODS: In a prospective contralateral-eye study performed under institutional review board supervision, 51 consecutive patients (102 eyes) had bilateral wavefront-guided LASIK for myopia using the Alcon LADARVision laser. One eye of each patient was randomized to have the flap created with the IntraLase femtosecond laser and the other flap using a standard compression head Hansatome microkeratome. All other treatment parameters were the same. RESULTS: The IntraLase group had significantly better mean uncorrected visual acuity (UCVA) at all intervals from 1 day to 3 months postoperatively. The mean spheroequivalent at 3 months was more myopic with the Hansatome (-0.34 diopter [D] +/- 0.28 [SD]) than with the IntraLase (-0.19 +/- 0.24 D) (P<.01). The mean residual astigmatism at 3 months was also significantly higher in the Hansatome group than in the IntraLase group (0.32 +/- 0.25 D and 0.17 +/- 0.20 D, respectively) (P<.01). The differences in UCVA persisted after spheroequivalent outcomes were controlled for but equilibrated when the analysis was modified to control for manifest postoperative astigmatism. Aberrometry showed significantly higher astigmatism and trefoil in the Hansatome group. Recovery of corneal sensation and epithelial integrity was similar between groups. CONCLUSIONS: The statistically better UCVA and manifest refractive outcomes after LASIK with the IntraLase femtosecond laser may be the result of differences in postoperative astigmatism and trefoil. These findings are consistent with previous findings of better astigmatic outcomes with the IntraLase laser and may have clinical significance for wavefront-guided treatments.     

LASIK术中不同制瓣方式对比敏感度的变化

目的对比分析准分子激光原位角膜磨镶术(laser in situ keratomileusis,LASIK)术中飞秒激光制瓣与传统微型角膜板层刀制瓣后对比敏感度变化。方法 Ziemer LDV飞秒激光制作角膜瓣组20例40眼患者作为飞秒组,传统微型角膜板层刀制作角膜瓣20例40眼患者作为板层刀组。所有病例使用同一台准分子激光机。比较术后2组患者的视力及对比敏感度。结果 LASIK术后1周,白天和夜晚状态下2组各空间频率的对比敏感度均较术前有明显下降,差异均有统计学意义(均为P<0.05),至术后3个月时,2组各空间频率对比敏感度恢复至术前水平。飞秒组夜晚带眩光状态各空间频率术后1周、术后1个月、术后3个月均高于术前水平,差异均有统计学意义(均为P<0.05)。板层刀组夜晚带眩光状态各空间频率术后1周下降,至术后1个月、3个月高于术前水平,差异均有统计学意义(均为P<0.05)。结论 LASIK术后对比敏感度会出现短暂下降,但是飞秒激光制瓣相对于板层刀制瓣术后对比敏感度恢复较快。     

Contrast sensitivity after LASIK flap creation with a femtosecond laser and a mechanical microkeratome

PURPOSE: To compare the effects on contrast sensitivity of the IntraLase femtosecond laser for flap creation (IntraLASIK) and standard LASIK for myopia. METHODS: Two hundred eyes of 100 consecutive patients underwent LASIK treatment using the VISX S2 laser system. The femtosecond laser (15 kHz IntraLase) was used for flap creation in 100 eyes (50 patients) and a mechanical microkeratome (Carriazo-Barraquer) was used in 100 eyes (50 patients). Best spectacle-corrected contrast sensitivity was measured before and 6 months postoperatively in the IntraLASIK and mechanical LASIK groups. The IntraLASIK and mechanical LASIK-induced changes in contrast sensitivity were compared under photopic (85 cd/m2) and mesopic (5, 2.5, and 0.1 cd/m2) conditions. RESULTS: Contrast sensitivity for eyes after IntraLASIK did not differ from preoperative values at the photopic level (85 cd/m2). However, under mesopic conditions, a statistically significant reduction (P < .01) in contrast sensitivity was found at high spatial frequencies (12 and 18 cpd), although no significant contrast sensitivity differences were observed at low and middle spatial frequencies (P > .01 for 1.5, 3, and 6 cpd). No statistically significant differences were found between IntraLASIK and mechanical LASIK for 1.5, 3, and 6 cpd at any luminance level (P > .01). IntraLASIK showed better contrast sensitivity than mechanical LASIK under mesopic conditions at 12 cpd and photopic and mesopic conditions at 18 cpd (P < .01). CONCLUSIONS: IntraLASIK surgery demonstrated better contrast sensitivity at high spatial frequencies under photopic and mesopic conditions than mechanical LASIK.     

Very high-frequency digital ultrasound measurement of the LASIK flap thickness profile using the IntraLase femtosecond laser and M2 and Carriazo-Pendular microkeratomes

PURPOSE: To evaluate the corneal aberrometric outcomes and corneal flap thickness profile after LASIK using three different devices for lamellar keratotomy: Moria M2 microkeratome, SCHWIND Carriazo-Pendular microkeratome, and IntraLase femtosecond laser. METHODS: Sixty-six myopic eyes of 33 patients who underwent LASIK with the SCHWIND ESIRIS excimer laser were enrolled in this study. Lamellar keratotomy was performed using three different devices that were assigned randomly to each patient: the Moria M2 microkeratome, SCHWIND Carriazo-Pendular microkeratome, and IntraLase femtosecond laser. The intended flap depth was 110 microm in all cases. Flap thickness profile, corneal aberrations, contrast sensitivity, and refractive outcomes were evaluated. RESULTS: Mean central flap thickness was 117.50 +/- 7.80, 118.08 +/- 8.34, and 115.95 +/- 6.22 microm for the M2, Carriazo-Pendular, and IntraLase systems, respectively. No significant differences were found among the groups. Nasal thicknesses were significantly larger for the M2 flaps compared to IntraLase (P < .05) and Carriazo-Pendular flaps (P = .046 only at 3-mm position). Temporal thicknesses were larger for the M2 flaps, although only differences between M2 and Carriazo-Pendular flaps reached statistical significance. Larger superior and inferior thicknesses were also observed for M2 flaps, although no statistically significant differences were found. Regarding corneal aberrometry, no statistically significant differences were observed in coma-like (P = .138) and spherical-like root-mean-square (P = .300). CONCLUSIONS: The M2, Carriazo-Pendular, and IntraLase systems create flaps of predictable thickness during lamellar keratotomy in LASIK. Additionally, the Carriazo-Pendular and IntraLase devices create flaps with a planar profile.     

In vivo corneal confocal microscopy comparison of intralase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis

PURPOSE: To assess and compare corneal modifications induced by IntraLase PulsionFS femtosecond laser and mechanical microkeratome Hansatome for laser in situ keratomileusis (LASIK) using the new-generation Heidelberg Retina Tomograph II (HRT II)/Rostock Cornea Module confocal microscope. METHODS: In this case-control study, 24 eyes of 12 patients were examined with the HRT II in the follow-up of IntraLase femtosecond laser for LASIK myopic surgery. Twenty eyes of 10 patients were also examined after microkeratome Hansatome-LASIK surgery. In both groups, the patients underwent the first follow-up examination on day 7 and the last 12 months after surgery. Morphologic modifications of corneal architecture were evaluated, and comparisons were made between the two flap-formation techniques. RESULTS: Evaluation of both groups on day 7 showed keratocyte transformation, most likely related to cellular activation beneath the interface. The flap margin after the IntraLase technique appeared microscopically as a clear-cut edge that included the epithelial plug. At month 2, secondary fibrosis, adjacent to the still well-defined IntraLase flap edge, was observed. This reaction diminished with time, leaving a fibrotic scar adjacent to a wound constriction originating from the surrounding stroma. The flap margin of the mechanical microkeratome had the appearance of a less clearly identified fibrotic scar with no epithelial plug. CONCLUSIONS: This study reveals morphologic similarities between the interfaces obtained by femtosecond laser and mechanical microkeratome, probably because the same excimer laser performed the photoablation. However, the IntraLase flap margin showed greater fibrotic scarring than that induced by the mechanical microkeratome.     

Factors influencing flap and INTACS decentration after femtosecond laser application in normal and keratoconic eyes

PURPOSE: To compare accuracy of LASIK flap and INTACS centration following femtosecond laser application in normal and keratoconic eyes. METHODS: This is a retrospective case series comprising 133 eyes of 128 patients referred for refractive surgery. All eyes were divided into two groups according to preoperative diagnosis: group 1 (LASIK group) comprised 74 normal eyes of 72 patients undergoing LASIK with a femtosecond laser (IntraLase), and group 2 (INTACS group) consisted of 59 eyes of 39 patients with keratoconus for whom INTACS were implanted using a femtosecond laser (IntraLase). Decentration of the LASIK flap and INTACS was analyzed using Pentacam. RESULTS: Temporal decentration was 612.56 +/- 384.24 microm (range: 30 to 2120 microm) in the LASIK group and 788.33 +/- 500.34 microm (range: 30 to 2450 microm) in the INTACS group. A statistically significant difference was noted between the groups in terms of decentration (P < .05). Regression analysis showed that the amount of decentration of the LASIK flap and INTACS correlated with the central corneal thickness in the LASIK group and preoperative sphere and cylinder in the INTACS group, respectively. CONCLUSIONS: Decentration with the IntraLase occurred in most cases, especially in keratoconic eyes. The applanation performed for centralization during IntraLase application may flatten and shift the pupil center, and thus cause decentralization of the LASIK flap and INTACS. Central corneal thickness in the LASIK group and preoperative sphere and cylinder in the INTACS group proved to be statistically significant parameters associated with decentration.     

Anterior chamber gas bubble formation during femtosecond laser flap creation for LASIK

PURPOSE: To report anterior chamber gas bubble formation during corneal flap creation in a myopic patient who underwent LASIK using a femtosecond laser (IntraLase). METHODS: A 30-year-old man underwent customized wavefront-guided LASIK for myopia. The IntraLase FS15 was used to create the corneal flap. RESULTS: During flap creation, gas bubble formation was noted in the anterior chamber, in addition to cavitation bubbles under the flap. Flap creation was successful and myopic ablation was uneventful. One day postoperatively, the flap was well apposed, and no air bubbles were present in the anterior chamber. CONCLUSIONS: Gas bubbles in the anterior chamber can be an infrequent occurrence during the use of femtosecond laser for corneal flap creation. Although gas bubbles do not hinder flap creation, their presence may interfere with eye-tracking mechanisms.     

First clinical results with the femtosecond neodynium-glass laser in refractive surgery

PURPOSE: We evaluated four femtosecond laser intrastromal cutting procedures: creation of a corneal flap for laser in situ keratomileusis (LASIK), tunnel and entry cut for intracorneal ring, corneal flap and removable lens for keratomileusis, and intrastromal ablation for myopia and hyperopia. METHODS: A clinical trial using a femtosecond surgical laser (IntraLase Corporation) was performed in partially sighted eyes. Femto-LASIK treatment was performed on 46 eyes up to -14.00 D; 16 patients received intracorneal ring segments (Femto-ICRS); 5 patients each with one highly myopic eye had femtosecond laser keratomileusis (FLK), and 13 patients each with one myopic or hyperopic eye had intrastromal ablation (ISPRK). In Femto-LASIK, excimer laser ablation was done under the flap. In Femto-ICRS, ring segments were introduced into the laser-created channels. In femtosecond laser keratomileusis, a lens-shaped block of stroma was removed manually from under the flap. RESULTS: No difference was found between the results obtained with Femto-LASIK and a standard microkeratome. No refractive effects occurred when the created flap was not elevated. In cases of Femto-ICRS and conventional ICRS produced the same refractive results. With Femto-ICRS, no intraoperative complications occurred and visual acuity improved immediately after surgery. In femtosecond laser keratomileusis, high myopia was corrected without using excimer laser ablation; centralization of the treatment area was excellent. In intrastromal ablation, 1 to 2 hours after surgery the corneas were highly transparent; refractive results were stable. CONCLUSIONS: Femtosecond lasers can produce precise intrastromal cutting, offering significant safety and other advantages (no razor blades, corneal trauma, partial resections, or sterilization issues) over current techniques.     

Incidence of diffuse lamellar keratitis after laser in situ keratomileusis associated with the IntraLase 15 kHz femtosecond laser and Moria M2 microkeratome

PURPOSE: To analyze the incidence of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK) performed with an IntraLase 15 kHz femtosecond laser (IntraLase, Corp.) or a Moria M2 mechanical microkeratome (Moria SA). SETTING: Vissum Madrid, Madrid, Spain. METHODS: This retrospective study compared the incidence of DLK in consecutive LASIK procedures performed with the IntraLase 15 kHz femtosecond laser (study group) or the Moria M2 microkeratome (control group). Two surgeons performed both types of surgeries (femtosecond laser and microkeratome) using the same excimer laser (Technolas 217, Bausch & Lomb). During the first week postoperatively, topical dexamethasone drops were applied 8 times daily in the femtosecond group and 4 times daily in the mechanical microkeratome group. RESULTS: A total of 2000 consecutive eyes were analyzed (1000 eyes in each group). Diffuse lamellar keratitis stage 2 developed in 1 patient in each group; DLK stage 3 developed in 4 patients in the study group and in no patient in the control group (P = .03). CONCLUSION: Despite more intense postoperative steroid treatment, DLK seemed to occur more frequently after LASIK performed with the IntraLase 15 kHz femtosecond laser than after LASIK performed with the Moria M2 microkeratome.     

Femtosecond laser in situ keratomileusis after radial keratotomy

PURPOSE: To assess the safety, efficacy, and predictability of femtosecond laser in situ keratomileusis (LASIK) in eyes with previous radial keratotomy (RK). SETTING: Hospital Virgen del Consuelo de Valencia, Valencia, and Vissum Instituto Oftalmológico de Alicante, Alicante, Spain. METHODS: This prospective study comprised 11 eyes of 7 patients with residual low myopia after previous RK who had surgery with the IntraLase femtosecond laser (IntraLase Corp.) and the Star 2 excimer laser (Visx, Inc.). Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), defocus equivalent, refraction, flap thickness, flap diameter, and intraoperative complications were evaluated over a minimum 6-month follow-up. RESULTS: Although the RK incisions opened in all eyes when the flap was lifted, LASIK was successfully completed in all cases. Mean flap thickness was 119 microm +/- 13 (SD). There were no cases of slipped flaps, microstriae, or epithelial ingrowth. Defocus equivalent was reduced from a mean of 2.51 +/- 0.62 diopters (D) to 0.52 +/- 0.28 D; 7 eyes (63.6%) were within +/-0.50 D, and 11 eyes (100%) were within +/-1.00 D. All eyes had 20/40 or better UCVA, although 2 eyes (18.1%) lost 1 line of BSCVA. CONCLUSIONS: The femtosecond laser was safely used to create thin LASIK flaps in eyes with previous RK. An increased postoperative inflammatory response may explain the loss of BSCVA in some cases. Efficacy and predictability of the procedure were comparable to those of LASIK after RK with mechanical microkeratomes.     

Confocal microscopy comparison of intralase femtosecond laser and Moria M2 microkeratome in LASIK

PURPOSE: To analyze the quality of LASIK flaps created using a femtosecond laser or a mechanical microkeratome. METHODS: A prospective study of consecutive bilateral LASIK flaps (100 patients) created with a 15 kHz femtosecond laser (IntraLase) or with a mechanical microkeratome (Moria M2) was performed. Outcome measures included visual and refractive outcomes, flap dimensions, and intraoperative complications. The first consecutive ten patients (20 eyes) were examined using confocal microscopy 1 and 3 months following surgery. RESULTS: No significant differences were noted in the visual outcomes between groups (t test, P > .05 for all comparisons). Analysis of superficial measurements revealed more round flaps and greater predictability in surface dimensions for the femtosecond laser group (t test, P = .016). Mean deviation of flap thickness from target was the same for both instruments, 10 microm, with greater variability for the mechanical microkeratome. The incidence of diffuse lamellar keratitis was significantly greater in the femtosecond laser group (17%) than in the mechanical group (0%) (chi-square test, P < .001). Confocal microscopy revealed a higher wound healing opacity index in the femtosecond laser group. CONCLUSIONS: Although the clinical results are similar, the femtosecond laser produces LASIK flaps with more accurate dimensions compared to the mechanical microkeratome.     

Comparison of corneal aberration changes after laser in situ keratomileusis performed with mechanical microkeratome and IntraLase femtosecond laser: 1-year follow-up

PURPOSE: To compare corneal aberration changes 1 year after myopic laser in situ keratomileusis (LASIK) performed with a mechanical microkeratome and IntraLase femtosecond laser. METHODS: Twenty four eyes of 15 patients underwent LASIK with the Hansatome microkeratome, and 23 eyes of 13 patients underwent LASIK with the IntraLase femtosecond laser. A standard ablation was performed with the Bausch & Lomb Technolas 217 excimer laser. Topography data were used to calculate corneal aberrations with a 3.0 mm and 5.00 mm pupil, before and 12 months after surgery. The increasing factor (IF), defined as the ratio between the postoperative and preoperative mean value of the optical aberration, was calculated. The method of Mulhern et al was used to evaluate the centration of ablation. The comalike aberration was correlated with the decentration of ablation. The Student t test was used for the statistical anaylsis. RESULTS: The postoperative mean decentration of ablation was <0.5 mm. The comalike aberration appeared to be positively correlated with the decentration of ablation in both groups with a 5.0-mm pupil (P < 0.05). With a 3.00-mm pupil, the comalike aberration changed in the Hansatome group, whereas with a 5.00-mm pupil, all aberrations statistically significantly changed in both groups (P < 0.05). The IF similarly increased in 2 groups for spherical-like aberration, whereas IF greatly increased for total and comalike aberrations in the Hansatome group. CONCLUSIONS: Wavefront corneal aberrations change significantly 1 year after myopic LASIK performed with the Hansatome microkeratome as well as with IntraLase femtosecond lasers. Both of the procedures induce higher-order aberrations in the anterior corneal surface, but the amount of comalike aberration increases more with the Hansatome mechanical microkeratome.     

Comparison of the IntraLase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis

PURPOSE: To compare clinical outcomes between the IntraLase femtosecond laser and the mechanical microkeratome for creating flaps during laser in situ keratomileusis. DESIGN: Nonrandomized clinical trial. METHODS: The study involved a total of 55 eyes of 30 patients, with 27 eyes of 16 patients comprising the microkeratome group and 28 eyes of 14 patients comprising the IntraLase group. Refractive errors, visual acuity, higher-order aberrations, contrast sensitivity, and corneal sensitivity were compared between the two groups. RESULTS: There were no statistically significant differences between the two groups in terms of refractive errors and postoperative uncorrected visual acuity. There was no loss of best-corrected visual acuity in either group. The higher-order aberrations were similar in both groups (P > .05), except for spherical aberration, which was greater in the microkeratome group (P < .05). In the IntraLase group, the contrast sensitivity value at 12 and 18 cycles per degree under mesopic conditions was significantly improved at three months postoperatively (P < .05). The IntraLase group showed faster corneal sensitivity recovery compared with the microkeratome group, and corneal sensitivity in the peripheral area was nearly normalized at three months postoperatively in the IntraLase group. CONCLUSIONS: The femtosecond laser may have advantages over the microkeratome in the flap-making procedure. However, the IntraLase femtosecond laser failed to have significant superiority over the mechanical microkeratome in clinical outcomes, except for faster recovery of corneal sensation, lesser degree of spherical aberration, and some contrast sensitivity value.     

飞秒激光和角膜板层刀制瓣LASIK术后临床效果的比较

目的：观察飞秒激光和角膜板层刀制瓣准分子激光原位角膜磨镶术(LASIK)术后的临床疗效。

方法：对本院眼视光中心行飞秒激光和角膜板层刀制瓣LASIK术的近视患者各50例100眼在术后1、3、6mo做裸眼视力、残余屈光度、干眼症调查、高阶像差检查。

结果：两组的裸眼视力及残留屈光度在术后6mo内差异均无统计学意义(P>0.05); 干眼症状调查显示：术后1、3mo,两组比较差异均有统计学意义(P<0.05); 术后6mo两组比较,差异无统计学意义(P>0.05); 两组术后1、3、6mo高阶像差与术前对比均增大,差异有统计学意义(P<0.05),两组术后1mo水平彗差、垂直彗差及球差之间差异均无统计学意义(P>0.05); 两组术后3、6mo水平彗差、垂直彗差之间差异均无统计学意义(P>0.05),但飞秒激光制瓣LASIK术球差变化值小于角膜板层刀制瓣LASIK术,差异有统计学意义(P<0.05)。

结论：飞秒激光制瓣LASIK术是一种安全、有效、稳定的手术方式,干眼症发生率低,术后视觉质量更优于角膜板层刀制瓣LASIK。     

Subconjunctival gas bubble Formation during LASIK flap creation using femtosecond laser

PURPOSE: To report a patient who developed subconjunctival gas bubble formation during creation of a LASIK corneal flap with the IntraLase femtosecond laser. METHODS: Case report of a 19-year-old-man with compound myopic astigmatism and a normal preoperative evaluation who underwent bilateral simultaneous LASIK. RESULTS: The IntraLase FS15 was used to create an 8.8-mm diameter superior flap. Laser settings were 110-microm depth, 1.70-mJ bed and side-cut energy, 12-microm spot separation, 10-microm line separation, 70 degrees side-cut angle, 240-microm pocket start width, and 200-microm pocket start depth. The procedure was uneventful in the right eye whereas subconjunctival air bubbles were observed along the corneal limbus in the left eye (no bubbles were seen in the peripheral cornea). The patient was examined 30 minutes later, and the subconjunctival bubbles could still be observed. By the next day, the bubbles had disappeared completely. Postoperative uncorrected visual acuity was 20/20 in both eyes. CONCLUSIONS: Subconjuctival bubbles can be found after LASIK flap creation with a femtosecond laser.     

Effect of age on visual and refractive results after LASIK: mechanical microkeratome versus femtosecond laser

AIM: To evaluate the effect of age on visual and refractive results after laser in situ keratomileusis (LASIK) obtained with a mechanical microkeratome or a femtosecond laser. METHODS: Retrospective, nonrandomized, cohort study. A total of 3826 eyes were included in the study (1725 eyes treated with mechanical LASIK and 2101 eyes treated with femtosecond LASIK). The relationship between patient age and the 3-month postoperative visual and refractive results of both procedures were analyzed by linear regression analysis. RESULTS: Three months postoperatively, we found a significant correlation between age and the postoperative spherical equivalent (SE; r2=0.004, P=0.006), efficacy (r2=0.006, P=0.001), and safety indexes (r2=0.05, P=0.0001) in the mechanical LASIK group. On the other hand, we found a significant correlation between age and the postoperative SE (r2=0.02, P=0.0001) and the efficacy index (r2=0.01, P=0.0001) but not the safety index in the femtosecond laser group. Mechanical LASIK provided slightly but significantly better efficacy and predictability in patients 18 to 40 years of age and femtosecond LASIK did so in patients older than 40 years of age. The femtosecond laser provided better safety results than the mechanical microkeratome in both age groups. CONCLUSION: A tendency toward undercorrection and less predictability is found with aging after myopic LASIK regardless of whether the flap was created with a mechanical microkeratome or a femtosecond laser. However, femtosecond laser provides significantly better outcomes in terms of efficacy, safety and predictability compared to mechanical microkeratome for the correction of myopia in patients over 40y.