BACKGROUNDIt is unclear whether a laser epithelial keratomileusis (LASEK) has any significant advantage over a photorefractive keratectomy (PRK) for correcting myopia. We undertook this meta-analysis of randomized controlled trials to examine possible differences in efficacy, accuracy, safety and side-effects between two methods, LASEK and PRK, for correcting myopia.

METHODSA systematic literature retrieval was conducted in the PubMed, EMBASE, Chinese Bio-medicine Database, and Cochrane Controlled Trials Register to identify potentially relevant randomized controlled trials. The statistical analysis was performed using a RevMan 4.2 software. The results included efficacy outcomes (proportion of eyes with uncorrected visual acuity (UCVA) > or = 20/20 at 1 month and 12 months post-treatment), accuracy outcomes (proportion of eyes within +/-0.50 diopters (D) of target refraction at 1 month and 12 months post-treatment), safety outcomes (loss of > or = 2 lines of best spectacle-corrected visual acuity (BSCVA) at > or = 6 months post-treatment), mean pain scores on day 1 post-treatment, and mean corneal haze scores at 6 and 12 months post-treatment.

RESULTSSeven articles describing a total of 604 eyes with myopia from 0 to -9.0 D were identified in this meta-analysis. The combined results showed that the efficacy and accuracy outcomes between the two groups at 1 month and 12 months post-treatment were comparable. No patient lost > or = 2 lines of BSCVA at > or = 6 months post-treatment in four relevant trials. Compared with PRK, LASEK did not relieve discomfort on day 1 post-treatment or reduce corneal haze intensity at 6 and 12 months post-treatment.

CONCLUSIONSAccording to the available data, LASEK does not appear to have any advantage over PRK for correcting myopia from 0 to -9.0 D. This meta-analysis focuses mainly on the comparison of the early, mid-term and mid-long term results of the two methods. Additional studies to compare the long-term (> one year) results should be considered.

Laser in situ kratomileusis(LASIK) is a prefered method to excimer laser photorefractive keratectomy (PRK) because the former cuts only corneal stroma, while the latter cuts corneal epithelium, Bowmans membrane, and stroma, LASIK is a complex procedure composed of corneal flap preparation and photo-ablation. In corneal flap preparation, two types, manual and automatic, of microkeratomes have been used. We experienced problems during and after LASIK procedure using a manual microkeratome in learning curve period(8 months) and criticized the problems to shorten a learning curve of manual microkeratome. One hundred eighty six myopic eyes treated with LASIK using manual microkeratome(MLK, SCMD, USA) from January 1997 to August 1997 by one operator(Joo) were subjects. Problems occurred in 24 eyes(12.9%) and consisted of hole in corneal flap (5 eyes), thin corneal flap(3 eyes), winkling of corneal flap (2 eyes), hinge inside optical zone of laser(3 eyes), haze of interface (3 eyes), and free corneal flap(8 eyes). Majority of complications occurred in the first 3 months and most complicated cases were preventable when the speed of microkeratome enhancement was slow in late series of study. It seems that a manual microkeratome takes longer learning curve than automated microkeratome. Therefore, to decrease the number of problem cases in learning curve of LASIK using manual microkeratome a didatic course, advices from experienced surgeons, and participation in wet lab would be mandatory.
Bowman Membrane ; Corneal Stroma ; Epithelium, Corneal ; Keratomileusis, Laser In Situ* ; Lasers, Excimer ; Learning Curve ; Methods ; Photorefractive Keratectomy

BACKGROUNDThin-flap laser in situ keratomileusis (LASIK) is the new trend of refractive error correction surgery, the formation of corneal flap is crucial for a success of LASIK surgery. This study aimed 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).

METHODSOne hundred and sixty-one eyes of 81 consecutive patients were enrolled in this prospective study and randomly divided into three groups depending on the flap creation method: flap creation with the the IntraLase femtosecond laser (IntraLase group, 59 eyes), flap creation with the Moria One Use-Plus SBK (SBK group, 44 eyes), and flap creation with the Moria M2 Single-Use 90 µm-head microkeratome (M2SU90 group, 58 eyes). The nominal flap thickness was 110 µm for all patients and for the three devices. One month after surgery, Visante OCT was used to measure the flap thickness at 20 locations on each cornea and the results were assessed for uniformity, regularity, and accuracy.

RESULTSAt 1 month after surgery, the mean central flap thickness was (111 ± 3) µm in the IntraLase group, (114 ± 8) µm in the SBK group, and (118 ± 13) 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 µm in the IntraLase group, 10 µm in the SBK group, and 20 µm in the M2SU90 group respectively. A difference greater than 20 µm was observed in 0.42% of measurements in the IntraLase group; 2.95% of the measurements in the SBK group and 21.12% of measurements in the M2SU90 group.

CONCLUSIONSThe 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.

OBJECTIVETo evaluate the clinical outcome among three different laser in situ keratomileusis (LASIK) ablations: Q-factor customized ablation (aberration smart ablation, ASA), wave-front guided ablation (WASCA) and ablation under wave-front guiding plus iris recognition system (IR+WASCA).

METHODSThis prospective study comprised 96 eyes of 96 patients, and they were randomly divided into three groups: 30 patients in ASA group, 32 in WASCA group, and 34 in IR+WASCA group. There were no any statistical differences in spherical equivalent (SE), age, sex, pupil diameter, higher-order aberrations (HOA) among three groups preoperatively. Wave-front analysis was performed before and 1, 3 months after operation.

RESULTAll patients got an uncorrected visual acuity (UCVA) ≥ 0.8 1 and 3 months after operation. The residual SE was in ± 0.50D both at 1 and 3 months after surgery. There was no statistical difference in SE value, HOA, change of HOA, and coma aberration postoperatively among three groups. Horizontal coma (Z3¹) aberration took the majority of coma. HOA, total coma aberrations and spherical aberration increased postoperatively (P = 0.000), but without significant difference between 1 month and 3 months after surgery.

CONCLUSIONThat three customized LASIK are all effective, safe, accurate and stable; meanwhile WASCA may have better UCVA than the other two groups postoperatively.

BACKGROUNDLaser in situ keratomileusis (LASIK) has become an efficient and commonly performed procedure to reduce refractive errors. In order to further increase the postoperative visual quality, the wavefront-guided refractive surgery has been a research hotspot in customized surgery. This study was conducted to compare the visual acuity, higher-order aberration, and contrast sensitivity of wavefront-guided LASIK with iris-registration and conventional LASIK.

METHODSTwo hundred and eleven myopic eyes of 109 patients were enrolled in this prospective study and randomly divided into two groups: the wavefront-guided LASIK (wg LASIK) group (94 eyes) and conventional LASIK group (117 eyes). A Wavescan Wavefront aberrometer was used to analyze Zernike coefficients and the root-mean-square (RMS) of higher order aberrations with 6.0 mm pupil size, and Optec 6500 visual function instrument was used to measure contrast sensitivity (CS) under 5 spatial frequencies before and after surgery in both groups.

RESULTSThe uncorrected visual acuity (UCVA) and the mean spherical equivalent (SE) in wg LASIK group were significantly better than those in conventional LASIK (UCVA, z = 2.339, P = 0.019; SE, t = 2.838, P = 0.005) at 3 months after surgery. Moreover, the increase in Z(3)(-3), Z(3)(1), Z(3)(3), Z(4)(0), Z(5)(-1), Z(5)(1), Z(5)(5) and Z(6)(-6) in wg LASIK group was statistically smaller than that in conventional LASIK group (P < 0.05). In wg LASIK group, eyes with a higher amount of the preoperative RMS of the higher order aberrations (RMSh = 0.30 microm) showed a statistically lower increase (13.5%) than those in conventional LASIK group at 3 months after surgery (33.3%) (P = 0.004). And the values of 4th order spherical aberration (4thSA) and the root mean square of 6th order aberration (RMS6) in wg LASIK group were significantly lower than those in conventional group in eyes which had higher preoperative astigmatism (= 1.0D) (4thSA, P = 0.03; RMS6, P = 0.02). Wg LASIK group showed better CS values than the correspondingly preoperative values at all spatial frequencies with and without glare at 3 months after the surgery while conventional LASIK group displayed reduced CS values except for 1.5 and 3 cycles per degree with glare. The differences between the two groups were statistically significant (P < 0.001).

CONCLUSIONSWavefront-guided LASIK with iris-registration is efficient to reduce higher order aberrations especially spherical and coma aberrations, and to improve postoperative visual acuity and contrast sensitivity compared with conventional LASIK. The application of wavefront-guided LASIK with iris-registration is particularly suitable for eyes with higher preoperative RMSh values and eyes with higher preoperative astigmatism.

The biomechanical properties of 21 white New Zealand rabbits' corneas after Laser in situ keratomileusis (LASIK) were tested by use of one-dimension tensile test and creep test in the INSTRON 5544 mechanical machine. The cornea-related data from the experiments of one-dimension tensile test and creep test for an hour were obtained; a standard linear solid model was adopted to analyse the data, and the least square method was used to fit the viscoelastical coefficients of creep experiment on different corneas. We noticed there was certain difference between the LASIK groups and the normal group in respect to the corneal modulus of elasticity, the stiffness coefficients diminished with the increase of ablation depth; the anti-tensile ability of corneas also displayed some reduction. These findings indicate that the deeper the ablation goes, the easier will be the deformation after LASIK.
Animals ; Biomechanical Phenomena ; Cornea ; physiopathology ; surgery ; Elasticity ; Keratomileusis, Laser In Situ ; methods ; Lasers, Excimer ; therapeutic use ; Rabbits

PURPOSETo verify whether there exists any difference in higher order aberrations after undergoing myopic LASIK (laser in situ keratomileusis) with conventional ablation and customized ablation in different eyes of the same patient.

METHODSThis was a prospective randomized study of 54 myopic eyes (27 patients) that underwent LASIK using the Nidek EC-5000 excimer laser system (Nidek, Gamagori, Japan). Topography-guided customized aspheric treatment zone (CATz) was used in the first eye of the patient (study group) and the other eye of the same patient was operated on with conventional ablation (control group). Higher order aberrations [root-mean-square (RMS) in the 5-mm zone] of both groups were observed with the Nidek OPD-Scan aberrometer before and 3 months after LASIK. Preoperative mean refractive error was similar between two eyes of the same patient (t=-0.577, P>0.05).

RESULTSPreoperatively, higher order aberrations (RMS in the 5-mm zone) in the CATz ablation and conventional groups were (0.3600+/-0.0341) microm and (0.2680+/-0.1421) microm, respectively. This difference was not statistically significant (t=1.292, P>0.05). Three months after LASIK, higher order aberrations (RMS in 5-mm zone) in the CATz ablation and conventional groups were (0.3627+/-0.1510) microm and (0.3991+/-0.1582) microm, respectively. No statistically significant difference was noted between pre- and postoperative higher order aberrations in the CATz group (t=-0.047, P>0.05). However, a statistically significant increase in higher order aberrations was observed after conventional ablation (t=-5.261, P<0.05). A statistically significant difference was noted in the increase of higher order aberrations after LASIK between groups (t=-2.050, P=0.045).

CONCLUSIONLASIK with conventional ablation and topography-guided CATz ablation resulted in the same BSCVA (best spectacle-corrected visual acuity) 3 month after LASIK. Higher order aberrations were increased, but the increase of higher order aberrations after customized ablation treatment was less than that after conventional ablation.

PURPOSE: To compare the changes in posterior corneal curvature using scanning slit topography (Orbscan II) and Scheimpflug imaging (Pentacam) before and after Epi-laser in situ keratomileusis (LASIK) for myopia. METHODS: In a prospective observational case-series study, 20 myopic patients having undergone Epi-LASIK were examined serially with two different devices, Orbscan II and Pentacam, preoperatively and one month postoperatively. Posterior central elevation (PCE) and posterior maximal elevation (PME) were compared between the two devices, and the changes in parameters after Epi-LASIK were analyzed using a difference map. RESULTS: All parameters (preoperative and postoperative PCE and preoperative and postoperative PME) that were measured using the Orbscan II were significantly greater compared to those of the Pentacam (for all p < 0.001). PCE and PME were significantly increased one month postoperatively in the Orbscan II measurements (p < 0.05) but were not significantly increased in the Pentacam measurements. Also, DeltaPCE and DeltaPME, in the difference map obtained by each serial scanning, were significantly greater in the Orbscan II measurements than with the Pentacam (p = 0.012, p = 0.016). CONCLUSIONS: The Pentacam measurements displayed significantly reduced values in all parameters related to posterior corneal elevation compared to those of the Orbscan II. The Pentacam showed no significant change in posterior corneal curvature after Epi-LASIK, based on the difference map.
Adult ; Corneal Topography/*methods ; Female ; Humans ; Keratomileusis, Laser In Situ/*methods ; Male ; Myopia/*surgery ; Prospective Studies ; Treatment Outcome

The excimer laser diopter correction has proven to be efficient and safe. This paper presents the principle of excimer laser refractive surgery. Based on analyzing the mathematics model of the human eye cornea, the authors have proposed a new model which can be used to proceed the myopia, hyperopia, astigmatism diopter correction. Also studied were the excimer laser's ablation mechanism and the flying-spot scanning technology. The research results have been directly applied to Ophthalmic excimer laser system. The correction of diopter is well improved.
Algorithms ; Cornea ; anatomy & histology ; Humans ; Keratomileusis, Laser In Situ ; methods ; Lasers, Excimer ; Models, Theoretical ; Photorefractive Keratectomy ; methods ; Refractive Surgical Procedures

The purpose of this study is to assess the efficacy of the multi-zone cross-cylinder method as compared with the single method for astigmatism correction using LASIK. This prospective study enrolled 40 patients (52 eyes) who underwent the cross-cylinder method using LASIK, and 52 patients (60 eyes) who underwent the single method using LASIK: all patients were given a diagnosis of complex myopic astigmatism from the department of ophthalmology of this hospital between January 2002 and July 2003. Preoperatively, the mean spherical equivalent refraction was .3.85 +/- 1.13 D in the cross-cylinder group and .4.05 +/-1.20 D in the single method group (p = 0.23). The mean cylinder was .2.05 +/-1.58 D in the cross-cylinder group and .1.95 +/-1.12 D in the single method group (p = 0.31). 6 months after treatment the results were a mean spherical equivalent refraction of .0.26 +/-0.30 D in the crosscylinder group and -0.34 +/-0.35 D in the single method group (p = 0.13). The mean cylinder was .0.38 +/-0.29 D in the cross-cylinder group and .0.45 +/-0.30 D in the single method group (p = 0.096). There were no statistically significant differences between the two groups. The mean BCVA was not different from mean preoperative BCVA in both groups (i.e., 0.98 +/-0.10, 0.96 +/-0.25, p = 0.86). Postoperatively, patient complications that included night halo, glare and corneal haze were not noted in either group. In conclusion, the results of cross-cylinder method are no different from the single method for the correction of a complex astigmatism. In the future, studies will have to be conducted to assess the efficacy of the cross-cylinder method in consideration of those factors that can affect the postoperative outcome.
Adult ; Astigmatism/*surgery ; Corneal Stroma/surgery ; Humans ; Keratomileusis, Laser In Situ/*methods ; Myopia/*surgery ; Postoperative Complications ; Prospective Studies