Effect of femtosecond laser and mechanical lamellar LASIK on the stability of corneal flap thickness / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To explore the effects of femtosecond laser and mechanical lamellar blade excision laser <i>in situ</i> keratomileusis(LASIK)on corneal flap thickness stability and dry eye syndrome.<p>METHODS: Retrospective analysis of 80 patients with myopia who underwent LASIK in our hospital. According to different methods of flapping, it is divided into femtosecond laser group and mechanical laminating knife group. The flap thickness of the two groups of patients at different time points(1h, 1d, 1wk, 1mo, 3mo)were measured. The differences in corneal apex 1, 2, 3mm and corneal apex flap thickness in different directions were compared. The incidence of dry eye syndrome was compared between 1 and 3mo, 1a, 2a after surgery.<p>RESULTS: The apex thickness of the corneal flap of the femtosecond laser group is 99.62±4.50μm, and the thickness of the apex of the mechanical lamellar knife group is 125.25±12.81μm.The thickness of the corneal flap at different centrifugal points of the femtosecond laser flap is relatively uniform, while the thickness of the corneal flap of the mechanical lamellar knife varies greatly. The OSDI scores of the mechanical lamellar group were higher than those of the femtosecond laser group at 1, 3, 1, and 2a postoperatively(<i>P</i><0.01). At 2a of follow-up, the incidence of dry eye in the femtosecond laser group was lower than that in the mechanical lamellar group(χ²=4.692, <i>P</i>=0.030). At 1 and 2a postoperatively, the proportion of mild dry eye in the femtosecond laser group was higher than that in the mechanical lamellar group(<i>P</i>=0.044, 0.001).<p>CONCLUSION: Compared with the mechanical lamellar scalpel, the corneal flap thickness of patients with femtosecond laser LASIK is better, more uniform and less error. And the incidence of dry eye after surgery is lower, with mild dry eyes.

Influenceofmicrokeratomeand femtosecond laser on vision and corneal flap thickness used in corneal flap making / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To study and compare the influence situation of corneal flap made by microkeratome and femtosecond laser for the vision and corneal flap thickness in patients. METHODS:Totally 120 patients(240 eyes) with myopic refractive surgery in our hospital from June 2014 to May 2015 were randomly divided into Group A (microkeratome group) with 60 cases (120 eyes) and Group B (femtosecond laser group) with 60 cases (120 eyes). Then the vision situation and corneal flap thickness indexes of two groups at different time after the treatment were compared. RESULTS:The vision situation between the two groups at different time after the treatment all had no significant differences (all P>0.05),while the corneal flap thickness related indexes of Group B at different time after the treatment were all better than those of Group A (all P<0 05). The evaluation indexes of two groups after the treatment all had significant differences (all P<0.05). CONCLUSION: The indexes of corneal flap made by femtosecond laser are better than those of microkeratome,and the influence of two methods for the vision is no obvious.

Effect of related factors on the stability of posterior corneal surface after LASIK / 国际眼科杂志(Guoji Yanke Zazhi)

AIM:To discuss the related factors that affected the stability of posterior corneal surface after laser in situ keratomileusis ( LASIK) . METHODS:About 64 patients (64 eyes) were enrolled. The correlation among the changes in posterior corneal surface 6 month after LASIK, surgery method, corneal flap thickness ( FT ) , ablation thickness ( AT ) , postoperative residual corneal stroma thickness ( RCST ) , preoperative thinnest corneal thickness ( CT ) , flap thickness/preoperative thinnest corneal thickness ( FT/CT ) , ablation thickness/preoperative thinnest corneal thickness ( AT/CT) , postoperative residual corneal stroma thickness/preoperative thinnest corneal thickness ( RCST/CT) , anterior and posterior preoperative corneal height, the difference of the forward shift in posterior corneal surface ( diff value ) of preoperative and preoperative intraocular pressure were analyzed. RESULTS: The changes of diff value between preoperative and postoperative were related with diopter (r=0.419, P=0.014), AT (r=0.394, P=0.023), AT/CT (r=0.501, P=0.004), Diff value of preoperative (r=0.501, P=0. 004), RCST (r=-0. 385, P=0. 033) and RCST/CT (r=-0. 401, P=0. 025). The changes of height value from posterior corneal surface between preoperative and postoperative were related with diopter (r=0. 520, P=0. 002), AT (r=0.504, P=0. 003), AT/CT (r=0. 442, P=0. 013), Diff value of preoperative (r=0. 624, P=0. 000) and RCST/CT (r=-0. 394, P=0. 028). CONCLUSION: AT, RCST, AT/CT, RCST/CT and diff value of preoperative should be the key index that predicted the stability of posterior corneal surface after LASIK,the further research will give the range of safety value.

Measurement and comparison of corneal flap thickness between Wavelight FS200 femtosecond laser and Moria 90 microkeratome LASIK by OCT / 中华实验眼科杂志

Background Lasein situ keratomileusi(LASIK) imainstream surgery forefractive correction,and femtosecond laseimuch often used to create thin corneal flap.The measuremenof OPTOVUE RTVue-100 OCto flap and stromal bed thicknesseofferuseful basifoLASIK.Ican be used in measuring the thicknesand shape of the corneal flap.Buthe study on the comparison of flap thicknesbetween WavelighFS200 femtosecond laseand MoriM2 microkeratome 90 μm-knife (Mori90 microkeratome) LASIK by OCilack.Objective The aim of thitrial wato compare the featureof corneal flapcreated by the WavelighFS200 femtosecond laseand Mori90 microkeratome.Methodpiloand prospective study wadesigned.Written informed consenwaobtained from each patienprioto LASIK.Sixty righeyeof 60 patientwith myopiomyopiastigmatism were enrolled in thiclinical trial.The patientwere randomized into the FS200 femtosecond lasegroup and Mori90 microkeratome group with matching demography.RTVue OCwaused to measure flap thicknesusing 10 settingon the 60 eye1 month afteoperation.The featureof the LASIK flapwere analyzed based on the measuring outcomes.ResultThe central flap thickneswa(112±3) μm and the mean flap thickneswa(112 ±3) μm in the FS200 femtosecond lasegroup,which wasignificanlowethan the central flap thicknesa(121±7) μm and the mean flap thicknesa(128±11) μm in the Mori90 microkeratome group respectively (P=0.031,0.030).Corneal flapin the FS200 femtosecond lasegroup showed flashape and thain the Mori90 microkeratome group wameniscushape.The central flap thickneswanoevidently differenfrom thaof peripheral thicknesin the FS200 femtosecond lasegroup (P =0.320).However,in the Mori90 microkeratome group,the central flap thickneswaobviously thinnethan thain the peripheral thicknes(P=0.038).The mean deviation between the actual and predicted flap thicknes(110 μm) wa(3±4)μm in the FS200 femtosecond lasegroup and (17±10) μm in the Mori90 microkeratome group,showing significandifference between them (P =0.009).ConclusionRTVue OCdeterminethathe shape of flapcreated by the FS200 femtosecond laseimore uniform and closeto the expected thicknesof 110 μm than the onecreated by the Mori90 microkeratome.OPTOVUE RTVue-100 OCiuseful tool to evaluate the flap shape and thicknesafteLASIK.

Comparison of flap thickness, visual outcomes, and higher order aberrations in eyes that underwent LASIK flap creation using a femtosecond laser versus a mechanical microkeratome

Objective@#To compare the predictability of flap thickness, visual and refractive outcomes, and higher order aberrations in eyes that underwent myopic LASIK using either a Technolas femtosecond laser or a Zyoptix XP mechanical microkeratome for flap creation.@*Methods@#The study involved a total of 44 eyes of 22 patients who underwent LASIK. Flap creation was randomized to using the Technolas femtosecond laser in one eye and Zyoptix XP microkeratome in the contralateral eye. Flap thickness was measured intraoperatively using ultrasonic pachymetry and postoperatively using the Visante ASOCT. Refractive outcome, visual acuity (VA), higher order aberrations, and contrast sensitivity were compared between the two groups.@*Results@#Twenty-two patients had LASIK for myopia or myopic astigmatism. Using ultrasonic pachymetry intraoperatively, the mean flap thickness was 134 (±10) um and 124 (±23) um in the femtosecond (FS) and microkeratome (MK) groups respectively. Comparing the deviation of the actual from the intended flap thickness, the FS group had statistically lower standard deviation compared to the MK group (p=0.04). Using the AS-OCT, the mean flap thickness at 3 months postoperatively was 119 (±10.82) um and 123 (±15.77) um in the FS and MK groups respectively. The difference in standard deviation between the two groups did not reach statistical significance (p=0.19). The mean spherical equivalent at 3 months was -0.45D (±0.42) and -0.13D (±0.16) respectively. Eightynine percent (89%) of eyes had uncorrected VA of 20/20 or better in both groups. All eyes attained best corrected VA of 20/20 or better in both groups. Differences in total higher order aberrations (p=0.09) and contrast sensitivity scores (p=0.47) were not statistically different between the two groups. @*Conclusion@#Flap thickness predictability was better using the Technolas femtosecond laser compared to the XP microkeratome blade. Visual and refractive outcomes, higher order aberrations, and contrast sensitivity were comparable between the 2 groups.

Comparison of Flap Thickness Measured with Ultrasound Subtraction Method, Direct Method, and Optical Coherence Tomography

PURPOSE: To compare the flap thicknesses measured with the ultrasound (US) subtraction method, the direct method, and optical coherence tomography (OCT) in femtosecond laser-assisted LASIK eyes. METHODS: The present study included 65 eyes of 37 patients who underwent femtosecond laser-assisted LASIK surgery. Flap thickness was measured intraoperatively using the direct and subtraction methods with US pachymetry and postoperatively using anterior segment OCT. Flap thickness measurements were compared among the three methods. RESULTS: There was no significant difference between the flap thickness measured using the US subtraction method and OCT (p = 0.511). The flap thickness values obtained by these two different methods also correlated well with each other (gamma = 0.820, p < 0.001). However, flap thickness measured using the US direct method was significantly different (p < 0.001) with a low agreement value compared to the other two methods. Furthermore, the US direct method showed a lower measurement success rate compared to the US subtraction method (54% vs. 95%). CONCLUSIONS: Flap thickness measured using the US subtraction method and OCT showed different values compared to that measured using the US direct method. Because of the lower measurement success rate and agreement value, the US direct method is not capable of being used in substitute for the US subtraction method.

Factors Influencing Corneal Flap Thickness in Laser In Situ Keratomileusis with a Femtosecond Laser

PURPOSE: To evaluate factors responsible for the variability between intended and achieved corneal-flap thickness during femtosecond laser-assisted laser in situ keratomileusis (LASIK). METHODS: A prospective, nonrandomized, case study was performed on 35 eyes of 18 consecutive patients who underwent LASIK surgery using the 60 kHz femtosecond laser microkeratome. Eyes were assigned to three different thickness groups, with 110-, 120-, or 130-microm cut depths. Anterior segment optical coherence tomography was used to assess the morphology of 35 LASIK flaps at postoperative one week postoperatively. The flap thickness was assessed at seven measuring points across each flap. Patient age, preoperative spherical equivalent, manual keratometry, preoperative central pachymetry, and regional variability of the cornea were evaluated to determine where they influenced the achieved corneal flap thickness. RESULTS: Cuttings of all flaps were easily performed without any intraoperative complications. Flap-thickness measurements had a mean of 115.21 +/- 4.98 microm (intended thickness, 110 microm), 121.90 +/- 5.79 microm (intended, 120 microm), and 134.38 +/- 5.04 microm (intended, 130 microm), respectively. There was no significant difference between the 110-microm and 120-microm groups when compared with the 130-microm group (one-way analysis of variance test, p > 0.05). Patients' age, preoperative spherical equivalent, manual keratometry, and preoperative central pachymetry did not affect the achieved flap thickness (Pearson correlations test, p > 0.05). The reproducibility of flap thickness in the central 1.5-mm radius area was more accurate than that in the peripheral 3.0 to 4.0-mm radius area (paired samples t-test, p < 0.05). CONCLUSIONS: Femtosecond laser-assisted LASIK is likely to reproduce a reliable thickness of the corneal flap, which is independent of corneal shape factors or refractive status. Future studies should focus on variations in corneal biomechanical factors, which may also play an important role in determining flap thickness.

Comparison of flaps created with the Moria M2 microkeratome with regular blade Versus Med-Logics 0 blade / 中华实验眼科杂志

BackgroundFlap creation is one of the most important steps during laser in situ keratomileusis (LASIK). As the microkeratome blade technology is developing, the accuracy, uniformity and reproducibility of corneal flaps created by the microkeratome blade are of high clinical concern. ObjectiveThe aim of this trial was to compare the features of corneal flaps created using the Moria M2 microkeratome 110 μm-knife with regular blade versus the Med-Logics O blade. MethodsA pilot and prospective study was designed. Two hundred and four eyes of one hundred and two patients were enrolled in this clinical trial. The patients were divided into the Moria M2 microkeratome 110 μm-knife with Med-Logics 0 blade group ( 110-0 group) ( 102 eyes) and Moria M2 microkeratome with 110 μm-knife with regular blade group (110 group) (102 eyes),with the matched demography. Fourier-domain optical coherence tomography ( RTVue OCT) was used to measure flap thickness using 28 settings on the 204 corneas at one week postoperatively. The features of the LASIK flaps were analyzed on the basis of the outcomes. Written informed consent was obtained from each patient prior to LASIK. Results There was no statistically significant difference in uncorrected visual acuity and the mean spherical equivalent between the 110-0 group and 110 group ( Z =-0. 375,P =0. 708 ; u =0. 056, P =0. 956 ) one week after LASIK. The mean flap thickness of the 110-0 group was considerably thinner than that of the 110 group ( 133.28+15.41μ m versus 142.81 ±10. 07μm) ( u =-5. 227,P＜0. 001 ). The corneal flaps in both the 110-0 group and in 110 group showed a meniscus shape. The nasal flap thickness of the right eyes was not evidently different from that of temporal ( P＞0. 05 ) , but in the left eyes, nasal flap thickness was obviously thicker than the temporal flap thickness (P＜0. 05) in both groups. The mean deviation between the achieved and attempted flap thickness ( 130 μm) were (17.46±2.28) μm in the 110-0 group and ( 16. 82±6. 12) μm in the 110 group, showing a significant difference between them ( u ==0. 517, P=0. 608 ).ConclusionsThe shape of flaps created using the Moria M2 110-0 is more uniform and closer to the expected thickness of 130 μm than the ones created using the Moria M2 110 microkeratome.

Effect of microkeratome suction duration on corneal flap thickness and diameter in pigs / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To determine the effect of suction duration on thickness and diameter of corneal flap created by microkeratome in porcine eyes in laser in situ kerato-mileusis (LASIK).METHODS: Sixty porcine eyes were randomly assigned to three groups according to different suction durations: group 1 (10 seconds), group 2 (20 seconds), and group 3 (30 seconds). A Moria M2 microkeratome (Moria, France) with a 160μm head was used to create a corneal flap. Corneal flap thickness was measured by automated ultrasonic pachymetry, and the flap diameter was measured by a vernier caliper.RESULTS: The flap thickness of group 1, group 2 and group 3 was 146.05±13.46μm, 157.35±18.95μm and 169.25±21.02μm, respectively. There was a statistically significant difference among three groups (P=0.001). The mean flap diameter in groups 1, 2 and 3 was 8.63±0.19mm, 8.89±0.24mm and 9.06±0.18mm, respectively. A statisti-cally significant difference was found among groups (P<0.01).CONCLUSION: In LASIK in porcine eyes, an increase in suction duration resulted in a thicker and greater flap.

Reproducibility of IntraLASIK Flap Thickness Measured with Optical Coherence Tomography

PURPOSE: To investigate the relationship among optical coherence tomography (OCT), ultrasound pachymetry, and Orbscan in central corneal thickness measurement and to evaluate the reproducibility of flap thickness using an IntraLase femtosecond laser. METHODS: Central corneal thickness was measured by OCT, ultrasound pachymetry, and Orbscan in 59 eyes of 30 patients before LASIK. After IntraLASIK, the corneal flap thickness measured using OCT was compared with the intended corneal flap thickness. RESULTS: Central corneal thickness measured by OCT was thinner than that measured by other instruments preoperatively, but there was no significant difference among these methods (p>0.01), and corneal thickness values obtained by ultrasound pachymetry and Orbscan correlated well with those obtained by OCT (r ranged from 0.804 to 0.889, p0.01). CONCLUSIONS: OCT is a relatively accurate instrument for measuring corneal thickness and can easily measure the corneal flap thickness after LASIK. Compared with the results of a previous study, the mean measured flap thickness in this study was more reproducible with the IntraLase femtosecond laser.

Preoperative Factors related to Corneal Flap Thickness in LASIK using Microkeratome

PURPOSE: To identify factors that may be related to variations in corneal flap thickness in LASIK using the Moria M2 microkeratome. METHODS: The charts of patients having LASIK based on steep keratometry nomogram using Moria M2 microkeratome (head : 110 micrometer) and excimer laser (VISX STAR S2, USA) in our department of ophthalmology from March, 2003, to May 2005, were reviewed retrospectively. A total of 195 eyes were enrolled in the investigation. We analyzed relationship between corneal flap thickness and preoperative factors including central corneal thickness, steep keratometer, corneal diameter, suction ring using multiple regression analysis. RESULTS: Mean corneal flap thickness was 119.37+/-21.21 micrometer. There was a statistically significant positive correlation between flap thickness and central corneal thickness (p<0.05). No correlation was found between flap thickness and other preoperative factors including steep keratometer, corneal diameter and suction ring. CONCLUSIONS: Mean corneal flap thickness using the Moria M2 110 micrometer head was 119.37+/-21.21 micrometer, little thicker than our expectation. When surgery is performed based on steep keratometry nomogram using Moria M2 microkeratome, if intraoperative factors are excluded, there is a trend toward thicker flap thickness with thicker central corneal thickness, whereas steep keratometer, corneal diameter or suction ring have no influence on flap thickness.

Contrast analysis of corneal flap thickness using Moria M290 and 110 microkeratome / 上海第二医科大学学报

Objective To analyze the corneal flap thickness in laser in situ keratomileusis(LASIK) using Moria M2 microkeratome and to identify the related factors. Methods Sixty patients with LASIK were divided into two groups: M2 90 group,using the Moria M2 90 microkeratome,n=30;M2 110 group,using the Moria M2 110 microkeratome,n=30.All were performed on both eyes with the right one treated first.Subtraction pachymetry was used to measure corneal flap thickness which was analyzed statistically with the data including age,preoperative corneal diameter,curvature,corneal thickness and refraction. Results In the 30 patients of M2 90 group,the mean corneal flap thickness of right eye and left eyes were(128.03?12.03)?m(105~156 ?m) and(123.40?12.38) ?m(92~147 ?m),respectively,and the corneal flap thickness were statistically different between the right and left eyes(P

Clinical Evaluation of New Microkeratome

PURPOSE: To determine dimensions and quality of flaps created with Zyoptix(TM) XP microkeratome. METHODS: Ninety-nine eyes of 50 patients were enrolled in this prospective study. LASIK procedures were performed by a single surgeon, using Zyoptix(TM) XP microkeratomes (Bausch & Lomb) with 160 micrometer, 180 micrometer and 200 micrometer heads and suction rings with intended flap diameters (IFD) of 8.5 mm and 9.5 mm. Patients' age, preoperative manifest refraction value, keratometry reading, preoperative central corneal thickness, stromal bed thickness, and flap diameter were recorded. To calculate flap thickness, subtraction pachymetry was used. The microscopic quality of the flap and stromal bed was graded from 0 to 100. RESULTS: The mean thickness of flaps created by Zyoptix(TM) XP microkeratome was 107.56+/-13.61 micrometer with the 160 micrometer head, 132.99+/-21.03 micrometer with the 180 micrometer head, and 134.32+/-14.75 micrometer with the 200 micrometer head. The actual flap diameter was 9.18 mm for an IFD 8.5 mm and 9.96 mm for an IFD of 9.5 mm. Subjective assessment of the flap and stromal bed, respectively, was 98.32+/-2.24 and 97.94+/-3.85 with the 160 micrometer head, 97.86+/-1.73 and 97.97+/-2.22 with the 180 micrometer head, and 97.79+/-1.17 and 97.72+/-1.10 with the 200 micrometer head. CONCLUSIONS: Flaps created with Zyoptix(TM) XP microkertome were reproducible in their dimensions. The flaps and stromal beds were of high quality.

The Availability and Safety of the Microkeratome in LASIK

PURPOSE: To evaluate the reproducibility of the flap thickness in LASIK using Moria M2 microkeratome and to examine the safety and the complication rate intraoperatively and postoperatively. METHODS: 92-Ninety-two consecutive eyes of 50 patients that received LASIK using the Moria M2 microkeratome were reviewed. The mean of the predictable corneal flap thickness was compared with the mean of the created corneal flap thickness, and intraoperative and postoperative complication and safety were evaluated. RESULTS: The average corneal flap thicknesses were 140+/-15.16 micrometer with 130 micrometer head and 108.01+/-16.72 micrometer with 110 micrometer head. There was no statistically significant correlation between the predictable corneal flap thickness and the created corneal flap thickness with the 130 micrometer head (p=0.001, one-sample t-test), but there was a stastistically significant correlation with the 110 micrometer head (p=0.573, one-sample t-test). CONCLUSIONS: The M2 Moria microkeratome created a desirable thickness with the 110 micrometer head, and we can expect postoperative stability of the remaining corneal thickness. The complication rate both intraoperatively and postoperatively was very low.

Comparison of Clinical Results of LASIK with Different Flap Thicknesses

PURPOSE: To evaluate the effect of corneal flap thickness on visual prognosis and complications in LASIK. METHODS: A total of 251 eyes of 129 patients who had been followed up for 6 months or more after LASIK were evaluated retrospectively. The eyes were classified into two groups: group A of 34 eyes with corneal flap thickness of 100 m or less and group B of 217 eyes with corneal flap thickness of more than 100 m. Clinical outcomes, including uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), spherical equivalent (SE), myopic regression and complications, were compared between the two groups. RESULTS: In groups A and B, UCVA improved from 0.08 +/- 0.04 and 0.08 +/- 0.02 before surgery to 0.84 +/- 16 and 0.88 +/- 21 6 months after surgery, and SE changed from -6.36 +/- 2.46D and 6.07 +/- 2.81D to 0.29 +/- 0.72D and -0.17 +/- 0.81D 6 months after surgery, respectively, but there were no statistically significant differences between the two groups. BCVA, myopic regression and the incidence of complications also did not show any statistical difference. CONCLUSIONS: LASIK can be performed safely under thin corneal flaps of 100 m or less to leave enough residual corneal thickness.

Corneal Flap Thickness according to Suction Time of Microkeratome in Porcine Eye

PURPOSE: The purpose of this study is to investigate the effect of the suction time in forming the corneal flap with microkeratome on the corneal flap thickness. METHODS: Thirty porcine eyes were randomly assigned into 3 groups according to suction duration: group 1(10 sec), group 2(35 sec) and group 3(60 sec). The Hansatome microkeratome with 160 plate and a suction ring with 8.5mm diameter were used to create corneal flap. The thickness of central cornea was measured with automated ultrasound pachymeter before the procedure. And after making the flap, the remained corneal thickness was measured with the same method. Then, the difference between the two values was thought to be the corneal flap thickness. RESULTS: The mean corneal flap thickness in group1, 2, and 3 were 91.0+/-24.1 micromiter, 110.1+/-8.9 mu m and 127.2+/-6.1 mu m, respectively. The difference was significant among the three groups(p=0.010), and the longer suction duration made the flap thicker. CONCLUSIONS: These results suggest that in forming the corneal flap with microkeratome, the suction duration has an effect on the corneal flap thickness and an increase of suction duration makes the flap thicker in porcine eyes.

Clinical feature of unintended thin corneal flap in LASIK: 1-year follow-up

To purpose of this study was to evaluate complications of unintended thin corneal flap in laser in situ keratomileusis (LASIK), such as visual acuity and myopic regression, at the one year follow-up. We performed a study on 54 eyes, i.e. 27 patients, having LASIK. The eyes were split into two groups, group one, 27 eyes with unintended thin corneal flap with a thickness of 100 microm or less, and as a control group, 27 eyes with a thickness of 110 microm or more. The average corneal flap thicknesses of the two groups were 88.89 +/- 8.07 microm and 132.70 +/- 19.58 microm, respectively. With regard to postoperative complications, there were no statistical differences between the groups for: foreign bodies in aspects of the interface, mild peripheral infiltration, superficial punctuate keratitis, myopic regression and decreased vision. The only complication showing any statistical difference between the two groups was the central corneal opacity. An unintended thin corneal flap, with an intact Bowman's layer, induced no significant postoperative complications. Central corneal opacity was apparent in 4 of the eyes in group one, so may be related with a thin corneal flap.

Clinical Outcome of LASIK with Different Flap Thickness

PURPOSE: Since a few cases of keratectasia after LASIK were reported, the importance of residual corneal thickness has been emphasized. This study was to analyze adverse effects which may occur in reducing corneal flap thickness to increase residual corneal thickness. METHODS: A total of 237 eyes of 149 patients who had been followed up for 6 months or more after LASIK were evaluated retrospectively. Intended corneal flap thickness was 130 micrometer in 116 eyes(group A), and 160 micrometer in 121 eyes(group B) using an Automated Corneal Shaper(Chiron, USA). Clinical outcomes were compared between two groups. RESULTS: Except for some cases with retinal complication after surgery, 3 eyes lost best-corrected visual acuity by 2 lines or more in group A and 1 eye in group B, which was not statistically significant.(p>0.05) Fourteen eyes lost 1 line or more best-corrected visual acuity by postoperative irregular astigmatism in group A and 10 eyes in group B, which showed no significant difference, either. The incidence of flap-related complications such as wrinkling and free cap did not differ significantly between two groups(p>0.05). CONCLUSIONS: To leave residual cornea of greater thickness using a 130 micrometer thick flap rather than 160 micrometer may be a useful method to avoid postoperative keratectasia, one of the most severe complications.

The Consistency of Corneal Flap Thickness and Size in LASIK using the Innovatome Automatic Micro keratome

To evaluate the consistency of the thickness and size of the corneal flap made by the Innovatome automatic microkeratome and to determine the cor-relation between preoperative variables and corneal flap dimensions, we per-formed the prospective study comprised 102 consecutive eyes of 51 patients having laser in-situ keratomileusis (LASIK)with the Innovatome microker-atome.Central corneal thickness, corneal curvature, and refractive error were measured preoperatively.All flaps were created using No.170 blades. The mean corneal flap thickness was 139.70 +/-2 2.5 6 micrometer, and the range was 93.0 ~193.7 micrometer.There was no relationship between the corneal flap thickness and the preoperative corneal curvature or spherical equivalent, but the corneal flap thickness increased with the preoperative central corneal thickness. The mean corneal flap size (vertical diameter)was 9.17 +/- 0.25 mm (range :8.5 0 ~9.7 5 mm).There was no relationship between the corneal flap diameter and the preoperative central corneal thickness or spherical equivalent, but the corneal flap size increased with the preoperative corneal curvature.