Journal of Refractive Surgery

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Original Article 

Safety and Effectiveness of Thin-Flap LASIK Using a Femtosecond Laser and Microkeratome in the Correction of High Myopia in Chinese Patients

Haiyan Li, PhD, MD; Tong Sun, MD; Ming Wang, PhD, MD; Jialiang Zhao, PhD, MD

Abstract

Purpose:

To establish safety and effectiveness of thinflap LASIK using a femtosecond laser and microkeratome in correcting high myopia in Chinese patients.

Methods:

Two hundred seventy-four eyes of 148 Chinese patients with high myopia whose spherical equivalent refraction (SE) ranged from −6.12 to −15.75 diopters (D) received thin-flap LASIK with the VISX S4 IR excimer laser system. Corneal flaps were created with a femtosecond laser (15-kHz IntraLase, 134 eyes of 76 patients, target flap thickness 100 μm) and Moria M2 microkeratome (90-μm head, 140 eyes of 72 patients, target flap thickness 110 μm). Clinical outcomes were assessed with uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), manifest refraction, wavefront aberrometry, Schirmer tests, and tear break-up time (TBUT) at 1 day, 1 week, and 1 and 3 months postoperatively.

Results:

At 3 months, both groups showed comparable clinical outcomes in most parameters assessed, including the percent of postoperative UCVA better than or equal to preoperative BSCVA (P=.642), mean residual spherical equivalent refraction (P=.448), mean Schirmer test (P=.950), and mean TBUT (P=.867). Postoperative coma, trefoil, and spherical aberration were similar in both groups (P=.202, P=.898, and P=.890, respectively). Both groups had a similar percent of eyes with a change of SE of <1.00 D (P=.284).

Conclusions:

Thin-flap LASIK with a femtosecond laser and microkeratome are both safe and effective for the correction of high myopia in Chinese patients. Femtosecond laser shows similar predictability, stability, and induction of higher order aberrations to the microkeratome.

Abstract

Purpose:

To establish safety and effectiveness of thinflap LASIK using a femtosecond laser and microkeratome in correcting high myopia in Chinese patients.

Methods:

Two hundred seventy-four eyes of 148 Chinese patients with high myopia whose spherical equivalent refraction (SE) ranged from −6.12 to −15.75 diopters (D) received thin-flap LASIK with the VISX S4 IR excimer laser system. Corneal flaps were created with a femtosecond laser (15-kHz IntraLase, 134 eyes of 76 patients, target flap thickness 100 μm) and Moria M2 microkeratome (90-μm head, 140 eyes of 72 patients, target flap thickness 110 μm). Clinical outcomes were assessed with uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), manifest refraction, wavefront aberrometry, Schirmer tests, and tear break-up time (TBUT) at 1 day, 1 week, and 1 and 3 months postoperatively.

Results:

At 3 months, both groups showed comparable clinical outcomes in most parameters assessed, including the percent of postoperative UCVA better than or equal to preoperative BSCVA (P=.642), mean residual spherical equivalent refraction (P=.448), mean Schirmer test (P=.950), and mean TBUT (P=.867). Postoperative coma, trefoil, and spherical aberration were similar in both groups (P=.202, P=.898, and P=.890, respectively). Both groups had a similar percent of eyes with a change of SE of <1.00 D (P=.284).

Conclusions:

Thin-flap LASIK with a femtosecond laser and microkeratome are both safe and effective for the correction of high myopia in Chinese patients. Femtosecond laser shows similar predictability, stability, and induction of higher order aberrations to the microkeratome.

From the Department of Ophthalmology, Shanghai AIER Eye Hospital, Shanghai, China (Li, Sun); Wang Vision Institute, Nashville, Tenn (Wang); and the Department of Ophthalmology, Peking Union Medical College Hospital, Tsinghua University, Beijing, China (Zhao).

The authors have no commercial, financial, or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (H.L., T.S., M.W., J.Z.); data collection (H.L., T.S., M.W., J.Z.); data analysis and interpretation (H.L., T.S., M.W., J.Z.); drafting of the manuscript (H.L., M.W.); critical revision of the manuscript (H.L., T.S., M.W., J.Z.); supervision (M.W.)

Correspondence: Haiyan Li, PhD, MD, No. 1286 Hongqiao Rd, Shanghai, China 200336. Tel: 86 137 64523896; Fax: 86 021 62190332; E-mail: lhypumc@hotmail.com

Received: February 11, 2008
Accepted: February 10, 2009
Posted Online: February 12, 2010

There is a greater prevalence of high myopia in the Chinese population than in the Caucasian population.1 For this group of patients, LASIK is the most popular keratorefractive surgical method with rapid visual recovery and less pain and discomfort. Alternative choices to LASIK include various surface treatments such as photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), and epi-LASIK, but suffer from limitations such as pain, slow recovery, and the risk of subepithelial haze, even with mito-mycin C, which is greater in patients with high myopia. The present study is focused on LASIK correction of high myopia in Chinese patients.

For high myopic correction, thin-flap LASIK is preferred over thick-flap because a thicker residual stromal bed can be maintained, thus reducing the risk of ectasia. Historically, the ideal flap thickness had been considered to be approximately 130 to 160 μm due to the ease with which the flap can be manipulated intraoperatively with better flap-to-bed fitting, fewer flap striae, and fewer intraoperative complications such as buttonholes, half-cuts, and steps.2 However, over the years, the disadvantages of thicker flaps have been increasingly recognized. Thicker flaps leave a thin stromal bed and can cause reduction in corneal long-term stability. Studies have shown that one of the most important risk factors for inducing postoperative LASIK corneal ectasia is insufficient residual stromal bed thickness.2–4

However, although a thin flap leaves a thicker stromal bed and a more stable cornea, it has traditionally been associated with some flap problems, including difficulty in manipulating thin flaps, increased risk of flap striae, flap displacement, and irregular astigmatism.2–4 Even so, improvements in microkeratome flap creation technology in recent years, including improved precision and accuracy and an increased amount of experience by surgeons in manipulating thin flaps, have led to a reduction of previously reported flap problems with thin flaps. For example, Kymionis et al2 reported a series of 33 eyes with LASIK flap thicknesses <80 μm. All cases had rapid visual rehabilitation with good predictability and stability over a long-term follow-up period. They found that the thinner flap resulted in less postoperative stromal edema and a better fit over the ablated corneal bed. Lin et al3 performed a retrospective review of 1131 eyes that underwent ultra-thin corneal flap LASIK with an average flap thickness of 87.3 μm. None of the eyes developed postoperative haze or striae, and all eyes had excellent visual results. Prandi et al4 also found that patients with flaps ≤100 μm had better functional results than those with thicker flaps. They found no statistically significant difference between intra- and postoperative complications between the groups with different flap thickness.

The advent of the femtosecond laser has ushered in a new era of precision and accuracy in flap creation for LASIK, providing an alternative and perhaps better way of creating LASIK flaps, particularly for thin flaps, for which a tighter control of flap thickness distribution is more critical. Based on published studies,5–8 it appears that the standard deviation or data spread of flap thickness is indeed much tighter with the femtosecond laser (IntraLase 15 kHz [Abbott Medical Optics, Santa Ana, Calif], 10.2 μm)7 than with the microkeratome (15 to 19.8 μm).5,6 In addition, Wang9 reported that the ratio of standard deviation of flap thickness distribution is in fact a gross underestimation of the advantages of the femtosecond laser (ie, IntraLase 15 kHz) over that of the microkeratome. He found that although the advantages are apparent based on standard deviation of flap thickness distribution (a ratio of standard deviation of the microkeratome over that of the femtosecond laser is 4:1), the femtosecond laser actually shows dramatically more significant advantages when evaluating the risk of clinically creating extremely thin or thick flaps. The ratio of risk of creating either dangerously thin or thick flaps with the microkeratome is 10:18 with respect to that of the femtosecond laser.9 Extremely thin flaps can cause buttonholes whereas extremely thick flaps can lead to keratoectasia.

The following study was performed to establish whether it is safe and efficacious to perform thin-flap LASIK in high myopic Chinese patients and to compare the results with flaps created for such treatments using the femtosecond laser and the microkeratome.

Patients and Methods

Study Population

This nonrandomized clinical trial involved 274 eyes of 148 patients with high myopia (mean spherical equivalent refraction: −8.94±1.74 diopters (D), range: −6.12 to −15.75 D) who were identified as good candidates for LASIK by history and eye examinations and who gave written informed consent. Patients were allocated into two groups (microkeratome and femtosecond laser) by their own choices. All patients were appropriately informed about the two LASIK methods and were asked to choose the technique they preferred. All procedures conformed to the Declaration of Helsinki requirements for research involving human subjects. Institutional review board/ethics committee approval was obtained. All patients received thin-flap LASIK from August 2005 to October 2006.

The femtosecond laser group comprised 134 eyes of 76 patients. Of these patients, 25 were men and 51 were women. Mean patient age was 28.7 years (range: 18 to 55 years). The microkeratome group comprised 140 eyes of 72 patients. Of these patients, 24 were men and 48 were women. Mean patient age was 29.1 years (range: 19 to 48 years).

Preoperative Examination

Preoperative examination included general medical and ophthalmic histories and concomitant medications. Before cycloplegia, all eyes were examined for manifest refraction, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), intraocular pressure (IOP), tear break-up time (TBUT), Schirmer test, corneal topography (Orbscan; Bausch & Lomb Inc, Rochester, NY), keratography (Zeiss Humphrey Systems, Carl Zeiss Meditec AG, Jena, Germany), axial length (IOLMaster, Carl Zeiss Meditec AG), wavefront aberrometry (WaveScan; VISX Inc, Santa Clara, Calif), and slit-lamp microscopy. After cycloplegia was obtained, all eyes had a cycloplegic refraction and dilated fundus examination. Central corneal thickness was measured with an ultrasonic pachymeter (UP-1000; NIDEK Co Ltd, Gamagori, Japan) after topical anesthesia.

Refractive stability was documented by a change of ≤1.00 D at least 2 years prior to the baseline examination. If the refractive change exceeded this criterion, surgery was rescheduled after refractive stability was achieved.

Surgical Technique

All procedures were performed by one surgeon (T.S.). The procedures were performed under topical anesthesia. For the microkeratome group, the flap was created with an automated oscillating microkeratome (Moria M2, 90-μm head; Moria Inc, Antony, France), with an intended flap thickness of 110 μm. The ring sizes used (from the standard choices of −1, 0, +1, and +2) followed the manufacturer’s guidelines based on preoperative corneal curvature. The blade was changed from eye to eye. The flaps were superiorly hinged. For the femtosecond laser group, corneal flaps were created with the 15-kHz IntraLase system. Flap thickness was programmed to 100 μm, the hinge angle was programmed to 45°, and the hinges were placed superiorly. The excimer laser ablation was completed with the VISX S4 IR system in a routine manner with normal spherocylindrical corrections but not wavefront-guided corrections, and the same nomogram was adapted to each group. All eyes were targeted for emmetropia. For both groups, corneal flaps were repositioned by rinsing them with balanced saline solution. No corneal contact lenses were applied to reposition the flaps.

Postoperative Follow-Up

Postoperative medications included ofloxacin 0.3%, tobramycin 0.3% and dexamethasone 0.1% eye drops (TobraDex; Alcon Laboratories Inc, Ft Worth, Tex), fluorometholone 0.1% eye drops, and artificial tears. Follow-up examinations were performed 1 day, 1 week, and 1, 3, 6, and 12 months postoperatively; however, only 3-month data for 274 eyes are presented. Follow-up examinations included manifest refraction, UCVA, BSCVA, TBUT, Schirmer test, wavefront aberrometry, and slit-lamp microscopy.

Statistical Analysis

All statistical analyses of clinical outcomes were carried out by SPSS version 11.0 (SPSS Inc, Chicago, Ill). Statistical tests were performed at the 95% confidence interval unless otherwise noted. Chi-square tests were used to compare the results of various groups, and unpaired t tests were used to compare means.

Results

Preoperative characteristics of the femtosecond laser and microkeratome groups are comparable.

Table 1 shows the preoperative examinations and ablation design in all 274 eyes enrolled in the study. All parameters were similar in both groups (P>.05).

Preoperative Characteristics and Ablation Design in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Table 1: Preoperative Characteristics and Ablation Design in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Postoperatively, the femtosecond laser and microkeratome groups showed comparable results in a majority of the clinical parameters assessed, including UCVA, refraction, percent of patients whose postoperative UCVA was better than preoperative BSCVA, Schirmer test, and TBUT.

With regard to safety, no sight-threatening complications occurred and no decrease in BSCVA was found in either group. No flap complications (eg, epithelial defects, microstriae, flap dislocation) were observed. No eye developed epithelial ingrowth, haze, or sterile interface inflammation.

Postoperative Uncorrected Visual Acuity and Refraction

Preoperative BSCVA and postoperative UCVA of the femtosecond laser group and the microkeratome group are shown in Figures 1 and 2. Table 2 shows the eyes whose postoperative UCVA is better than or equal to preoperative BSCVA. Uncorrected visual acuity on postoperative day 1 with the femtosecond laser was inferior to UCVA with the microkeratome, but the difference was not statistically significant. Uncorrected visual acuity in the two groups tended to be more similar with time.

Preoperative Best Spectacle-Corrected Visual Acuity (BSCVA) and Postoperative Uncorrected Visual Acuity (UCVA) in the Femtosecond Laser Group. Preoperatively, 120 (89.6%) of 134 Eyes Had BSCVA 20/20 or Better. Postoperatively, the Number of Eyes with UCVA 20/20 or Better Was 94 (70.1%) at 1 Day, 110 (82.1%) at 1 Week, 116 (86.6%) at 1 Month, and 111 (82.8%) at 3 Months.

Figure 1. Preoperative Best Spectacle-Corrected Visual Acuity (BSCVA) and Postoperative Uncorrected Visual Acuity (UCVA) in the Femtosecond Laser Group. Preoperatively, 120 (89.6%) of 134 Eyes Had BSCVA 20/20 or Better. Postoperatively, the Number of Eyes with UCVA 20/20 or Better Was 94 (70.1%) at 1 Day, 110 (82.1%) at 1 Week, 116 (86.6%) at 1 Month, and 111 (82.8%) at 3 Months.

Preoperative Best Spectacle-Corrected Visual Acuity (BSCVA) and Postoperative Uncorrected Visual Acuity (UCVA) in the Microkeratome Group. Preoperatively, 116 (82.9%) of 140 Eyes Had Bscva 20/20 or Better. Postoperatively, the Number of Eyes with UCVA 20/20 or Better Was 102 (72.9%) at 1 Day, 112 (80.0%) at 1 Week, 121 (86.4%) at 1 Month, and 121 (86.4%) at 3 Months.

Figure 2. Preoperative Best Spectacle-Corrected Visual Acuity (BSCVA) and Postoperative Uncorrected Visual Acuity (UCVA) in the Microkeratome Group. Preoperatively, 116 (82.9%) of 140 Eyes Had Bscva 20/20 or Better. Postoperatively, the Number of Eyes with UCVA 20/20 or Better Was 102 (72.9%) at 1 Day, 112 (80.0%) at 1 Week, 121 (86.4%) at 1 Month, and 121 (86.4%) at 3 Months.

Eyes with Postoperative Uncorrected Visual Acuity Better than or Equal to Preoperative Best Spectacle-Corrected Visual Acuity in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Table 2: Eyes with Postoperative Uncorrected Visual Acuity Better than or Equal to Preoperative Best Spectacle-Corrected Visual Acuity in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

The postoperative refractive results are listed in Table 3. No significant difference was found in the refractive outcomes of both groups at 1 week and 3 months postoperative. With regard to postoperative astigmatism, comparison of the magnitude of the postoperative cylinders between the two groups shows comparable results with no statistical differences.

Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Table 3: Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Pre- and Postoperative Tear Film Comparison

As shown in Table 4, the preoperative Schirmer tests of the femtosecond laser group and microkeratome group were not significantly different, nor were they for the Schirmer tests and TBUTs for the two groups 3 months postoperatively.

Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Table 4: Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

The postoperative Schirmer tests were lower than the preoperative measurements in the femtosecond laser (t=3.968, P<.001) and microkeratome groups (t=5.969, P<.001). The postoperative TBUTs were faster than the preoperative measurements in the femto-second laser (t=3.740, P<.001) and microkeratome groups (t=4.339, P<.001).

The femtosecond laser group showed similar predictability and stability and induction of higher order aberrations to the microkeratome group.

Predictability

Figure 3 shows the comparison of predictability between the femtosecond laser and microkeratome groups according to the achieved correction (3 months postoperative) versus the intended correction. The trend line formula for the femtosecond laser group is y = 1.0003x − 0.4169; whereas for the microkeratome group it is y = 0.9355x + 0.0599.

Refractive Predictability Results Were Similar in the Femtosecond Laser (blue Diamonds) and Microkeratome (pink Squares) Groups (intended vs Achieved Correction).

Figure 3. Refractive Predictability Results Were Similar in the Femtosecond Laser (blue Diamonds) and Microkeratome (pink Squares) Groups (intended vs Achieved Correction).

Additionally, in the femtosecond laser group, the percentage of eyes with a spherical equivalent refraction of ±0.50 D and ±1.00 D at 3 months postoperatively was 60.4% (81 eyes) and 87.3% (117 eyes), respectively. In the microkeratome group, the percentage of eyes with a spherical equivalent refraction of ±0.50 D and ±1.00 D at 3 months postoperatively was 57.9% (81 eyes) and 82.9% (116 eyes), respectively. The differences between the two groups were not significant (χ2=0.190, P=0.713; χ2=1.069, P=.315).

Stability

Figure 4 shows the comparison of stability between the femtosecond laser group and microkeratome group. At 3 months postoperative, 112 (83.6%) of 134 eyes in the femtosecond laser group and 109 (77.9%) of 140 eyes in the microkeratome group had a change in spherical equivalent refraction of <1.00 D (χ2=1.438, P=.284).

Refractive Stability Results Were Similar in the Femtosecond Laser (blue Diamonds) and Microkeratome (pink Squares) Groups (spherical Equivalent Refraction from 1 Day to 3 Months Postoperative).

Figure 4. Refractive Stability Results Were Similar in the Femtosecond Laser (blue Diamonds) and Microkeratome (pink Squares) Groups (spherical Equivalent Refraction from 1 Day to 3 Months Postoperative).

Higher Order Aberration

Table 5 shows the pre- and postoperative higher order wavefront aberration measurements, including total root-mean-square (RMS) values and RMS values of coma, trefoil, and spherical aberration. No significant differences were noted between the femtosecond laser group and microkeratome group before LASIK. The postoperative total higher order RMS values were statistically lower in the femtosecond laser group than those in the microkeratome group (P=.034), but the difference might be below a clinically meaningful level. Postoperative coma, trefoil, and spherical aberration were similar in both groups (P=.202, P=.898, P=.890, respectively). In both groups, the total higher order RMS values were increased (P=.025, P<.001), the coma values were increased (P=.003, P=.002), and the spherical values were increased (P=.005, P=.002), but the trefoil values did not change significantly (P=.058, P=.837).

Pre- and Postoperative Higher Order Wavefront Aberration Measurements in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Table 5: Pre- and Postoperative Higher Order Wavefront Aberration Measurements in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Discussion

The present study of thin-flap LASIK using the femtosecond laser and microkeratome in correcting high myopia in Chinese patients shows that both methods are safe and effective. In terms of safety, no vision-threatening complications occurred in either the femtosecond laser group or microkeratome group. No loss of BSCVA was noted in any of the patients in either group. In terms of efficacy, the two flap creation methods showed comparable results in the majority of postoperative outcomes assessed, including UCVA, refraction, percent of patients who had better postoperative UCVA than preoperative BSCVA, Schirmer test, and TBUT. The femtosecond laser group demonstrates slightly better, though not statistically significant, predictability and stability, as well as less induction of higher order aberrations, which is statistically significant, but may be below a clinically meaningful level.

Comparing our results with those found in the literature, we discovered that our findings are similar to those found in several studies in non-Chinese populations.10–14 These studies demonstrated that the femtosecond laser was a good choice for corneal flap creation in LASIK, and the results were similar or superior to those completed with the microkeratome. However, our present study results differ in some aspects when compared with those in the literature. For example, Durrie and Kezirian12 and Kezirian and Stonecipher13 both found that the mean astigmatism results were significantly better in the femtosecond laser group than in the microkeratome group. We failed to note any significant difference in astigmatic refractive outcomes between the femtosecond laser and microkeratome groups. With regard to the postoperative higher order aberrations, Durrie and Kezirian12 found significantly higher trefoil aberrations in the microkeratome group, whereas Lim et al14 found that only the spherical aberrations were statistically greater in the microkeratome group. In contrast, however, Kezirian and Stonecipher13 did not find any significant difference in these parameters in the femtosecond laser and microkeratome groups.

Many reasons account for the differences observed in these studies, as well as when compared with the outcomes of our current study. First, the available published reports on LASIK with the femtosecond laser were all studies on Caucasian patients with mild to moderate myopia, whereas our present study was conducted only on high myopic patients and was done in a Chinese population. Second, the differences of the higher order aberrations observed in different studies could be related to the differences in the actual wavefront aberrometers used. Third, with regard to ocular surface health, previous studies showed a faster recovery in corneal sensitivity in LASIK with the femtosecond laser than with the microkeratome.14 However, corneal sensitivity was not measured in our study. On the other hand, we used dry eye assessment to provide an indirect parameter of the ocular surface health. We found that the Schirmer test and TBUT are, in fact, similar in the femtosecond laser and microkeratome groups. Possible reasons to account for this difference between the reported studies on ocular surface and that of our study may be related to our relatively short follow-up time of 3 months. Furthermore, we believe that theoretically one might not expect that these ocular surface health parameters be significantly different between the femtosecond laser and microkeratome groups, as the two groups have comparable mean flap thickness and hence, one would expect a comparable impact on the postoperative ocular surface conditions.

This study represents the first comprehensive study of LASIK with femtosecond laser thin-flap creation in a Chinese Mainland population, where high myopia is prevalent. In addition, because the femtosecond laser is not yet widely available in China, although its use is rising, this present study may help guide Chinese surgeons in the process of learning to use this new technology.

The femtosecond laser has some drawbacks when used for LASIK in a study like this, including a longer suction duration time than the microkeratome, slight increase in the incidence of diffuse lamellar keratitis, and a slower visual recovery process than with the microkeratome. Fortunately, the long duration of suction has recently been significantly alleviated with the advent of the faster 60-kHz IntraLase system. We anticipate that in the next few years, China will adopt the increased use of the femtosecond laser as has the rest of the world.

Our present study has some shortcomings that need improvement. First, our study is nonrandomized because our criteria of entrance into the femtosecond laser and microkeratome groups were dictated by the level of understanding and comfort for a new technology such as the femtosecond laser by a patient, as well as its financial affordability. However, we do not expect this nonrandomized patient selection process to fundamentally affect the conclusion of this study, as the preoperative parameters of the femtosecond laser and microkeratome groups were comparable. Another shortcoming of this study is the lack of corneal flap thickness measurement intraoperatively for all patients. However, because the flap thickness itself is not a parameter that we evaluated in this study, we believe that the absence of flap thickness measurement does not affect its basic conclusion. We did, nevertheless, perform a small sub-study (unpublished data, 2005) in which we measured intraoperatively the stromal bed thickness prior to the excimer treatment, and found that overall it generally agreed with the findings of others in the literature5,15 for both the femtosecond laser and microkeratome groups. Aside from these two shortcomings, a relatively short follow-up of the present study is possibly a third drawback. Longer follow-up in a larger study is needed in the future.

The present study represents the first of its kind in thin-flap LASIK in a high myopic Chinese population. The knowledge we gained in this study will likely help the process of introduction and education of Chinese surgeons in the understanding and adopting of this new laser technology. Our study shows that thin-flap LASIK with both the femtosecond laser and microkeratome is safe and effective.

References

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  2. Kymionis GD, Tsiklis N, Pallikaris AI, Diakonis V, Hatzithanasis G, Kavroulaki D, Jankov M, Pallikaris IG. Long-term results of superficial laser in situ keratomileusis after ultra-thin-flap creation. J Cataract Refract Surg. 2006;32:1276–1280. doi:10.1016/j.jcrs.2006.02.054 [CrossRef]
  3. Lin RT, Lu S, Wang LL, Kim ES, Bradley J. Safety of laser in situ keratomileusis performed under ultra-thin corneal flaps. J Refract Surg. 2003;19:S231–S236.
  4. Prandi B, Baviera J, Morcillo M. Influence of flap thickness on results of laser in situ keratomileusis for myopia. J Refract Surg. 2004;20:790–796.
  5. Aslanides IM, Tsiklis NS, Astyrakakis NI, Pallikaris IG, Jankov MR. LASIK flap characteristics using the Moria M2 microkeratome with the 90-micron single use head. J Refract Surg. 2007;23:45–49.
  6. Giledi O, Mulhern MG, Espinosa M, Kerr A, Daya SM. Reproducibility of LASIK flap thickness using the Hansatome microkeratome. J Cataract Refract Surg. 2004;30:1031–1037. doi:10.1016/j.jcrs.2003.09.070 [CrossRef]
  7. Binder PS. One thousand consecutive IntraLase laser in situ keratomileusis flaps. J Cataract Refract Surg. 2006;32:962–969. doi:10.1016/j.jcrs.2006.02.043 [CrossRef]
  8. Stonecipher K, Ignacio TS, Stonecipher M. Advances in refractive surgery: microkeratome and femtosecond laser flap creation in relation to safety, efficacy, predictability, and biomechanical stability. Curr Opin Ophthalmol. 2006;17:368–372. doi:10.1097/01.icu.0000233957.88509.2d [CrossRef]
  9. Wang M. Femtosecond technology. Refractive Eyecare. 2003;7:1–4.
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  11. Tan CS, Au Eong KG, Lee HM. Visual experiences during different stages of LASIK: Zyoptix XP microkeratome vs. IntraLase femtosecond laser. Am J Ophthalmol. 2007;143:90–96. doi:10.1016/j.ajo.2006.08.023 [CrossRef]
  12. 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. doi:10.1016/j.jcrs.2004.09.046 [CrossRef]
  13. Kezirian GM, Stonecipher KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. J Cataract Refract Surg. 2004;30:804–811. doi:10.1016/j.jcrs.2003.10.026 [CrossRef]
  14. Lim T, Yang S, Kim M, Tchah H. Comparison of the IntraLase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis. Am J Ophthalmol. 2006;141:833–839. doi:10.1016/j.ajo.2005.12.032 [CrossRef]
  15. Sutton G, Hodge C. Accuracy and precision of LASIK flap thickness using the IntraLase femtosecond laser in 1000 consecutive cases. J Refract Surg. 2008;24:802–806.

Preoperative Characteristics and Ablation Design in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Mean±Standard Deviation (Range)
tPValue
Femtosecond Laser GroupMicrokeratome Group
Sphere (D)−8.48±1.74 (−13.62 to −6.12)−8.42±1.56 (−14.75 to −6.12)0.313.754
Cylinder (D)−1.03±0.78 (−4.25 to 0)−0.94±0.80 (−4.75 to 0)0.930.353
Spherical equivalent refraction (D)−8.99±1.85 (−14.62 to −6.12)−8.88±1.64 (−15.75 to −6.62)0.506.614
Preoperative pachymetry (μm)540.0±30.6 (478 to 610)544.8±30.9 (482 to 659)1.287.199
Maximum corneal ablation depth (μm)115.7±17.3 (79 to 163)112.1±14.1 (75 to 157)1.855.065
Estimated residual corneal bed thickness (μm)324.1±19.4 (292 to 376)322.6±23.6 (285 to 422)0.575.566

Eyes with Postoperative Uncorrected Visual Acuity Better than or Equal to Preoperative Best Spectacle-Corrected Visual Acuity in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Time PostopNo. Eyes (%)
χ2PValue
Femtosecond LaserMicrokeratome
1 day73 (54.5)92 (65.7)3.609.065
7 days96 (71.6)108 (77.1)1.089.333
1 month109 (81.3)111 (79.3)0.183.762
3 months108 (80.6)116 (82.9)0.234.642

Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

1 Week
3 Months
Femtosecond LaserMicrokeratomePValueFemtosecond LaserMicrokeratomePValue
Sphere (D)0.02±0.76 (−3.00 to +4.00)0.02±0.85 (−3.50 to +2.00).971*−0.17±0.71 (−2.00 to +2.00)−0.26±0.86 (−3.00 to +1.75).342*
Cylinder (D)−0.60±0.34 (−1.75 to 0)−0.61±0.41 (−3.00 to 0).813*−0.64±0.38 (−2.00 to 0)−0.60±0.40 (−2.50 to 0).402*
SE (D)−0.28±0.76 (−3.75 to +1.63)−0.29±0.79 (−3.63 to +1.50).924*−0.49±0.70 (−2.38 to +1.38)−0.56±0.83 (−3.25 to +1.25).448*
SE ±0.50 D111 eyes (82.8%)109 eyes (77.9%).36281 eyes (60.4%)81 eyes (57.9%).713

Postoperative Refractive Results in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Preoperative
3 Months Postoperative
Femtosecond LaserMicrokeratomePValue*Femtosecond LaserMicrokeratomePValue*
Schirmer test (mm)12.9±7.113.2±7.9.7909.5±4.09.5±7.2.950
TBUT (s)10.0±4.210.6±6.4.5277.9±4.38.1±5.5.867

Pre- and Postoperative Higher Order Wavefront Aberration Measurements in 274 High Myopic Chinese Eyes that Underwent LASIK with a Femtosecond Laser or Microkeratome

Mean±Standard Deviation (μm)
tPValue
Femtosecond LaserMicrokeratome
Preoperative
  Root-mean-square0.382±0.1390.342±0.1251.014.316
  Coma0.188±0.1350.231±0.1151.178.245
  Trefoil0.178±0.1120.141±0.0751.327.191
  Spherical aberration0.098±0.1850.081±0.1170.384.703
Postoperative
  Root-mean-square0.480±0.1330.578±0.1692.188.034
  Coma0.333±0.1400.394±0.1781.296.202
  Trefoil0.141±0.0830.144±0.0760.128.898
  Spherical aberration0.205±0.1390.197±0.2430.139.890
Authors

From the Department of Ophthalmology, Shanghai AIER Eye Hospital, Shanghai, China (Li, Sun); Wang Vision Institute, Nashville, Tenn (Wang); and the Department of Ophthalmology, Peking Union Medical College Hospital, Tsinghua University, Beijing, China (Zhao).

The authors have no commercial, financial, or proprietary interest in the materials presented herein.

Correspondence: Haiyan Li, PhD, MD, No. 1286 Hongqiao Rd, Shanghai, China 200336. Tel: 86 137 64523896; Fax: 86 021 62190332; E-mail: lhypumc@hotmail.com

10.3928/1081597X-20100121-05

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