Anterior segment optical coherence tomography measurement of LASIK flaps: femtosecond laser vs microkeratome

Femtosecond Lasers in Cornea & Refractive Surgery

Since the introduction of femtosecond laser (FS) systems for corneal flap creation in laser-assisted in-situ keratomileusis there have been numerous applications for FS laser in corneal surgery. This manuscript details the utility of FS lasers in corneal surgical procedures including refractive laser surgeries, intracorneal ring segment tunnels, presbyopic treatments, and FS-assisted keratoplasty. We also review the role of FS lasers in diagnostic procedures such as two photon excitation fluorescence and second harmonic generation.

Validity of percentage tissue altered as a screening formula for post laser-assisted in-situ keratomileusis ectasia in Indian eyes

Purpose:

To calculate a modified percentage tissue altered (mPTA) in post laser-assisted in-situ keratomileusis (LASIK) eyes and to validate its role as an independent factor to evaluate ectasia in the Indian population.

Methods:

A total of 333 consecutive eyes with normal preoperative corneal topography by combined placido and scheimpflug imaging-based topography system (SIRIUS) who underwent LASIK using a microkeratome between 2011 and 2014 at a tertiary level teaching hospital in south India, were retrospectively analyzed. Preoperatively patient's refraction, flap thickness (FT), ablation depth (AD), residual stromal bed (RSB), and thinnest corneal thickness (TCT) were recorded. The formula used was mPTA = (FT + AD)/TCT. mPTA was grouped into <0.4 (low risk), 0.40 - 0.45 (moderate risk), and >0.45 (high risk). All patients were called for follow-up and underwent a topography to look for ectasia.

Results:

In total 60.1%, 29.1%, and 10.8% patients had mPTA of <0.4, 0.40 - 0.45 and >0.45, respectively. However, after a minimum follow-up of 2 years, none of the patients had any sign of ectasia.

Conclusion:

Careful selection of patients is mandatory before proceeding for LASIK. Factors like corneal thickness, RSB, degree of myopia, and AD are more important. The role of mPTA >0.4 as an independent risk factor for post LASIK ectasia is questionable in Indian eyes. Other factors or a modified formula suitable for Indian eyes needs to be investigated. A larger follow-up period is also required as ectasia has been known to develop even after 2 years.

Comparison of visual performance recovery after thin-flap LASIK with 4 femtosecond lasers

AIM

To compare the speed of visual recovery following myopic thin-flap LASIK with four femtosecond lasers.

METHODS

Eighty-eight eyes of 46 patients who were consecutively scheduled for bilateral LASIK with the IntraLase FS60 (Group 1), Femto LDV Crystal Line (Group 2), Wavelight FS200 (Group 3) and VisuMax (Group 4) femtosecond lasers were enrolled in. Monocular uncorrected distance visual acuity (UDVA), best-corrected distant visual acuity (CDVA), refraction, contrast sensitivity and higher-order aberrations (HOAs) were evaluated at 1, 3d, 1wk and 1mo postoperatively.

RESULTS

Sixteen eyes (72.7%) achieved 20/16 and 8 eyes (36.4%) were 20/12.5 at 1d in Group 2, which was significantly more than other 3 groups. At 1wk, 20 eyes (90.9%) achieved 20/16 in Groups 2 and 4. At 1mo, 20 eyes (90.9%) achieved 20/16 in Group 2 and Group 4, which were significantly more than other two groups. While by 1 mo, the difference of the residual spherical equivalent (SE) was not statistically significant among 4 groups (P=0.121). The induction of spherical aberration (SA) were significantly less for Groups 2, 3, 4 than for Group 1 one day after surgery (P=0.015). The differences among 4 groups were not statistically significant before and after surgery on every time points (all P>0.05).

CONCLUSION

The thin-flap LASIK procedure using the Femto LDV Crystal Line and VisuMax femtosecond laser show faster visual performance recovery.

Comparison of microkeratome assisted sub-Bowman keratomileusis with photorefractive keratectomy

Purpose

To compare the outcomes of photorefractive keratectomy (PRK) and thin-flap Laser-Assisted in Situ Keratomileusis/sub-Bowman keratomileusis (SBK) with intended flap thicknesses of 100 μm using the One Use-Plus SBK microkeratome.

Methods

Ninety-eight eyes of 52 subjects with myopic manifest refraction spherical equivalent (MRSE) of up to −5 diopters (D), a stable refraction for 1 year and a corrected distance visual acuity (CDVA) of at least 20/20 in each eye which had undergone SBK or PRK were reviewed retrospectively. Primary outcome measures were MRSE, uncorrected distance visual acuity (UDVA), CDVA, pachymetry and higher order aberrations (HOA). All patients were seen at 1 and 3 days, 1 week, and 1, 3, and 6 months after surgery.

Results

Both MRSE and UDVA showed a statistically significant improvement at postoperative 1, 3 and 6 months from baseline in both SBK and PRK groups. At postoperative 6 months, 100% of eyes were within ±0.50 D of attempted correction in both groups. However, SBK group demonstrated better outcomes with 81% of eyes within ±0.13 D, compared to 70% eyes in the PRK group. Both SBK and PRK group demonstrated similar refractive astigmatism accuracy at postoperative 6 months, with 88% of eyes having cylindrical error ⩽0.25 D. None of eyes lost any lines of CDVA in the PRK, and 2% eyes lost one line of CDVA in SBK group at postoperative 6 months.

Conclusion

The visual and refractive outcomes after both PRK and microkeratome assisted SBK are comparable, albeit with a higher complication rate in the SBK group.

Visual outcomes after femtosecond laser in situ keratomileusis flap complications

PURPOSE

To compare visual outcomes in normal and complicated laser in situ keratomileusis (LASIK) flaps constructed with a femtosecond laser.

SETTING

Wilford Hall Ambulatory Surgical Center, San Antonio, Texas.

DESIGN

Retrospective chart review.

METHODS

The main outcome measures were uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (CDVA) at 1 month post-surgery, which were compared in patients with and without complications during flap creation.

RESULTS

This retrospective chart review identified 586 eyes of 293 consecutive patients who had bilateral simultaneous femtosecond LASIK for myopia. A normal flap was attained in 539 (91.8%) of patients. At 1 month postoperatively, the mean UDVA was 20/19.1, and the CDVA was 20/16.8. 3 (0.51%) of patients experienced an incomplete side cut or intraoperative flap tear (the mean 1-month uncorrected distance visual acuity [UDVA] was 20/17.5 and the corrected distance visual acuity [CDVA] was 20/16.9 in both groups). Microstriae were seen in 28 (4.8%) of patients (mean 1-month UDVA, 20/21.7; CDVA, 20/17.4). Diffuse lamellar keratitis appeared in 4 (0.68%) of patients (mean 1-month UDVA, 20/21.7; CDVA, 20/15.6). Epithelial ingrowth developed in 9 (1.5%) of patients (mean 1-month UDVA, 20/18.7; CDVA, 20/16.9). There was no statistically significant difference in UDVA or CDVA at 1 month postoperatively between complicated and uncomplicated flaps (P > .05), and complicated flaps did not lose a statistically significant amount of CDVA or low-contrast acuity (CDVA 5%) compared to preoperative values.

CONCLUSIONS

Intraoperative and postoperative complications of LASIK flaps created with the femtosecond laser were rare, and their visual outcomes were equivalent to those of normal flaps.

FINANCIAL DISCLOSURE

Charles D. Reilly is a consultant to Alcon Labs and Abbott Medical Optics at present, but was not at the time of the study. For the remaining authors none are declared.

Comparison of corneal flaps created by Wavelight FS200 and Intralase FS60 femtosecond lasers

AIM

To assess and compare the morphology of corneal flaps created by the Wavelight FS200 and Intralase FS60 femtosecond lasers in laser in situ keratomileusis (LASIK).

METHODS

Four hundred eyes of 200 patients were enrolled in this study and divided into Wavelight FS200 groups (200 eyes) and Intralase FS60 groups (200 eyes). Fourier-domain optical coherence tomography (RTVue OCT) was used to measure the corneal flap thickness of 36 specified measurements on each flap one week after surgery. Results were used to analyze the regularity, uniformity and accuracy of the two types of LASIK flaps.

RESULTS

The mean thickness of corneal flap and central flap was 105.71±4.72 µm and 105.39±4.50 µm in Wavelight FS200 group and 109.78±11.42 µm and 109.15 ±11.59 µm in Intralase FS60 group, respectively. The flaps made with the Wavelight FS200 femtosecond laser were thinner than those created by the Intralase FS60 femtosecond laser (P=0.000). Corneal flaps in the 2 groups were uniform and regular, showing an almost planar configuration. But the Wavelight FS200 group has more predictability and uniformity of flap creation. The mean deviation between achieved and attempted flap thickness was smaller in the Wavelight FS200 group than that in the Intralase FS60 group, which were 5.18±3.71 µm and 8.68±7.42 µm respectively. The deviation of more than 20 µm was 0.2% measurements in Wavelight FS200 group and 8.29% measurements in Intralase FS60 group.

CONCLUSION

The morphologies of flaps created by Wavelight FS200 are more uniform and thinner than those created by Intralase FS60.

Flap-induced astigmatism in eyes with sphere myopia correction: Superior hinge using a rotating microkeratome versus nasal hinge using a linear microkeratome

PURPOSE

To compare the effect of a rotating microkeratome (M2) and a linear microkeratome (SBK) on the change in the astigmatic component in eyes with preoperative plano refractive cylinder.

SETTING

University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.

DESIGN

Retrospective case series.

METHODS

An Allegretto excimer laser was used to perform laser ablation in myopic eyes of consecutive patients. The laser in situ keratomileusis (LASIK) procedure included mechanical flap preparation using a microkeratome, either a linear type with a single-use 90 μm head to create a nasal hinge or a rotating type with a single-use 90 μm head to create a superior hinge. The Alpins vector method was applied to describe the effects of LASIK on postoperative refractive cylinder.

RESULTS

The study evaluated 1045 eyes of 852 patients. Although the mean overall efficacy and safety indices indicate the procedure was highly precise, safe, and efficient, there were statistically significant differences in surgically induced astigmatism (SIA) between the microkeratomes (P = .002). The postoperative refractive cylinder (ie, SIA) was 0.75 diopter (D) or more in 116 eyes (11.1%), 44 (12.8%) of 344 linear cases and 72 (10.3%) of 701 rotating cases. Independent of the type of microkeratome used, the SIA was slightly higher in eyes treated first; the mean magnitude of the induced astigmatism was 0.35 D.

CONCLUSIONS

In approximately 10% of eyes with preoperative plano refractive myopia, the astigmatic component tended to be overcorrected. Nevertheless, independent of the type of microkeratome, the maximum mean magnitude of refractive cylinder documented was 0.35 D.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Femtosecond laser in refractive and cataract surgeries

In the past few years, 9 unique laser platforms have been brought to the market. As femtosecond (FS) laser-assisted ophthalmic surgery potentially improves patient safety and visual outcomes, this new technology indeed provides ophthalmologists a reliable new option. But this new technology also poses a range of new clinical and financial challenges for surgeons. We provide an overview of the evolution of FS laser technology for use in refractive and cataract surgeries. This review describes the available laser platforms and mainly focuses on discussing the development of ophthalmic surgery technologies.

Using femtosecond laser to create customized corneal flaps for patients with low and moderate refractive error differing in corneal thickness

This study is designed to evaluate the visual outcomes, accuracy, and predictability of corneal flaps with different thicknesses created by 60-kHz femtosecond laser according to different corneal thicknesses in the patients with low and moderate refractive error. A total of 182 eyes were divided according to the central corneal thickness (470 μm-499 μm in Group A, 500 μm-549 μm in Group B, and 550 μm-599 μm in Group C) and underwent femtosecond laser-assisted LASIK for a target corneal flap thickness (100 μm for Group A, 110 μm for Group B, and 120 μm for Group C). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and refractive status were examined. The flap thickness of each eye was measured by anterior segment optical coherence tomography (AS-OCT) on 30 points at 1-month follow-up to assess the accuracy and predictability. Postoperatively, at least 75% of eyes had a UDVA of 20/16 or better, less than 2% of eyes lost one line, over 30% of eyes gained one or more lines in CDVA, at least 95% of eyes had astigmatism of less than 0.25 D, all eyes achieved a correction within ± 1.00 D from the target spherical equivalent refraction. The visual and refractive outcomes did not differ significantly in all groups (P >0.05). The mean flap thickness was 100.36 ± 4.32 μm (range: 95-113 μm) in Group A, 111.64 ± 3.62 μm (range: 108-125 μm) in Group B, and 122.32 ± 2.88 μm (range: 112-128 μm) in Group C. The difference at each measured point among the three groups was significant (P < 0.05). The accuracy and predictability were satisfactory in all three groups. In conclusion, this customized treatment yielded satisfactory clinical outcomes with accurate and predictable flap thickness for patients with low and moderate refractive error.

A comparison of LASIK flap thickness and morphology between the Intralase 60- and 150-kHz femtosecond lasers

PURPOSE

To prospectively compare the achieved thickness and consistency of LASIK flaps created with a 60- and 150-kHz femtosecond laser.

METHODS

One hundred twenty eyes of 60 patients with myopia were treated with LASIK. One eye had flap created by the Intralase FS 60-kHz femtosecond laser (Abbott Medical Optics, Abbott Park, IL) and the fellow eye was treated with the IntraLase iFS 150-kHz femtosecond laser (Abbott Medical Optics). Eyes were randomized according to ocular dominance. Flap morphology and measurements were taken with anterior segment optical coherence tomography (AS-OCT) at the 1-month postoperative visit.

RESULTS

AS-OCT showed similar regular planar morphologies in both groups. The mean thickness of the flaps in the FS 60 group was significantly higher than that of the iFS 150 group (105.4 ± 3.9 μm vs 103.9 ± 4.8 μm, P = .009). The mean deviation from targeted flap thickness was not significantly different between the two groups.

CONCLUSIONS

The Intralase iFS 150-kHz femtosecond laser creates flaps of similar thickness and uniformity to the Intralase FS 60-kHz femtosecond laser.

Effect of corneal hydration on the quality of the femtosecond laser anterior lamellar cut

The goal of this study was to assess the effect of corneal hydration on the quality of the femtosecond laser (FSL) anterior lamellar cut. The Visumax FSL was used to dissect an 8-mm-diameter corneal flap in 22 eye bank corneas showing various levels of hydration. The intended ablation depth was 220 µm in all eyes, which corresponded to the maximal depth available with this laser. After the cut, the achieved ablation depth was measured using optical coherence tomography images, flap separability was assessed by measuring the mean force generated to detach the flap, and stromal bed roughness was assessed by measuring the Haralick contrast level on the 1000× scanning electron microscopy images of the ablated surfaces. The preoperative central corneal thickness ranged from 547 to 1104 µm (mean ± SEM: 833 ± 30 µm). A negative correlation was found between the level of corneal hydration and the ablation depth measured in the mid-peripheral cornea (r =  -0.626, p = 0.003), the ablation being more superficial in more edematous corneas. The Haralick contrast also tended to increase as a function of corneal hydration (r = 0.416, p = 0.061), suggesting that laser ablation in edematous corneas results in rougher stromal surfaces. These results support the hypothesis that the quality of the FSL lamellar cut decreases as the level of corneal hydration increases. Although FSL is still considered in the field as the tool of the future for corneal dissection, a better understanding of the limits of this tool will be needed before it can replace manual or automated stromal dissection techniques in hydrated corneas.

Comparison of corneal flap thickness using a FS200 femtosecond laser and a moria SBK microkeratome

AIM

To evaluate differences in flap thickness resulting from use of an Alcon Wavelight FS200 femtosecond laser and a MORIA SBK microkeratome when making a 110-µm-thick corneal flap and to identify the potential factors that affect corneal flap thickness.

METHODS

A prospective case study was performed on 120 eyes of 60 patients who were divided into two groups for LASIK, each group consisting of 60 eyes (30 patients). The corneal flaps were created using an Alcon Wavelight FS200 femtosecond laser or a MORIA SBK microkeratome. The central corneal flap thickness was calculated by subtraction pachymetry. Age, central corneal thickness (CCT), spherical equivalent refraction, mean keratometry, and corneal diameter were recorded preoperatively for analysis.

RESULTS

Cutting of all flaps was easily performed without intraoperative complications. In the Alcon Wavelight FS200 femtosecond laser group, the mean right and left corneal flap thicknesses were 114.0±6.6 µm (range: 98-126) and 111.4±7.6 µm (range: 98-122), respectively. The difference (2.6±9.1 µm) in the corneal flap thickness between the right and left eyes was not significant (t=1.59, P=0.12). Stepwise regression analysis indicated that the resulting corneal flap thickness was unrelated to the patient's age, preoperative CCT, spherical equivalent refraction, mean keratometry, or corneal diameter. In the MORIA SBK microkeratome group, the mean right and left corneal flap thicknesses were 110.6±7.4 µm (range: 97-125 µm) and 108.2±6.1 µm (range: 78-123 µm), respectively. The difference in the corneal flap thickness between the right and left eyes (2.4±6.5µm) was not significant (t=2.039, P=0.0506). The corneal flap thickness was positively correlated with the preoperative CCT through stepwise regression analysis (r=0.297, P=0.021). The corneal flap thickness was not related to age, spherical equivalent refraction, mean keratometry, or corneal diameter. The corneal flap thickness was estimated using the following equation: Tflap=67.77+0.076 CCT (F=5.63, P=0.021).

CONCLUSION

Both the Alcon Wavelight FS200 femtosecond laser and the MORIA SBK microkeratome produced 110-µm-thick corneal flaps. The central corneal flap thickness was positively correlated with the preoperative CCT in MORIA SBK microkeratome surgery.

Image-guided evaluation and monitoring of treatment response in patients with dry eye disease

BACKGROUND

Dry eye disease (DED) is one of the most common ocular disorders worldwide. The pathophysiological mechanisms involved in the development of DED are not well-understood, and thus treating DED has been a significant challenge for ophthalmologists. Most of the currently available diagnostic tests demonstrate low correlation to patient symptoms and have low reproducibility.

METHODS

Recently, sophisticated in vivo imaging modalities have become available for patient care, namely, in vivo confocal microscopy (IVCM) and optical coherence tomography (OCT). These emerging modalities are powerful and non-invasive, allowing real-time visualization of cellular and anatomical structures of the cornea and ocular surface. Here we discuss how, by providing both qualitative and quantitative assessment, these techniques can be used to demonstrate early subclinical disease, grade layer-by-layer severity, and allow monitoring of disease severity by cellular alterations. Imaging-guided stratification of patients may also be possible in conjunction with clinical examination methods.

CONCLUSIONS

Visualization of subclinical changes and stratification of patients in vivo allows objective image-guided evaluation of tailored treatment response based on cellular morphological alterations specific to each patient. This image-guided approach to DED may ultimately improve patient outcomes and make it possible to study the efficacy of novel therapies in clinical trials.

Comparison of corneal flap morphology using AS-OCT in LASIK with the WaveLight FS200 femtosecond laser versus a mechanical microkeratome

PURPOSE

To evaluate and compare the thickness and the morphology of femtosecond and mechanical microkeratome LASIK flaps using anterior segment optical coherence tomography (AS-OCT).

METHODS

Bilateral LASIK was performed in 132 eyes from 61 myopic patients. Flaps were created in 72 eyes using the WaveLight FS200 femtosecond laser (Wave-Light GmbH, Erlangen, Germany) and in 50 eyes using the Moria microkeratome (Moria SA, Antony, France). AS-OCT was used 1 week postoperatively to evaluate the thickness of 17 points across each flap, which were 0, 2, and 3.5 mm to the corneal vertex on the horizontal, vertical, 45°, and 135° meridians.

RESULTS

The mean central flap thickness was 105.53 ± 5.86 μm in the WaveLight group and 132.96 ± 13.91 μm in the Moria group (P < .001). The difference between the achieved and the intended flap thickness (accuracy) was 6.17 ± 3.98 and 23.60 ± 12.64 μm, respectively (P < .001). The standard deviation within individual flap (uniformity) was smaller in the WaveLight group. The symmetry and regularity were also better in the WaveLight group. Flap morphology showed a more regular planar shape in the WaveLight group and a meniscus shape in the Moria group.

CONCLUSIONS

AS-OCT showed that the flaps created by the WaveLight femtosecond laser were more accurate, reproducible, and uniform than those created by the Moria microkeratome.

WaveLight FS200 vs Hansatome LASIK: intraoperative determination of flap characteristics and predictability by hand-held bioptigen spectral domain ophthalmic imaging system

PURPOSE

To intraoperatively determine and compare the characteristics and predictability of LASIK flaps made by the WaveLight FS200 femtosecond laser (Alcon Laboratories Inc) and Hansatome (Bausch & Lomb) microkeratome using a hand-held spectral domain ophthalmic imaging system (Bioptigen Inc).

METHODS

Sixty eyes from 30 patients undergoing bilateral LASIK were prospectively evaluated. Patients were divided into two equal groups to undergo flap creation with either 100-microm femtosecond laser flaps (FS flap group) or 120-microm microkeratome flaps (MK flap group). Flap thickness was measured intraoperatively after creation of the flap but prior to lifting using the hand-held probe of the spectral domain imaging system. Geometry of the flap edge and smoothness of the stromal bed after lifting the flap was also evaluated in all cases.

RESULTS

Mean difference between planned and achieved flap thickness in the paracentral region was 2.84 +/- 3.16 mm for the FS flap group and 11.33 +/- 10.27 mm for the MK flap group, whereas in the periphery, it was 5.72 +/- 3.26 mm in the FS flap group and 24.67 +/- 10.35 mm in the MK flap group. The differences between groups were statistically significant (P < 0.001, Kruskal-Wallis test). The edges of the flaps were vertical in the FS flap group and the stromal bed was smoother, whereas in the MK flap group, the edges were more sloping and the stromal bed more irregular.

CONCLUSIONS

The WaveLight FS200 femtosecond laser is able to produce planar flaps with a high degree of predictability between the desired and achieved flap thickness. The ability to study the flap characteristics intraoperatively (when flap edema and stromal bed hydration changes have not yet occurred) with the hand-held probe of the Bioptigen imaging system ensures greater accuracy than measurements done postoperatively using other anterior segment optical coherence tomography prototypes.

Femtosecond laser technology in corneal refractive surgery: a review

PURPOSE

To discuss current applications and advantages of femtosecond laser technology over traditional manual techniques and related unique complications in corneal refractive surgical procedures, including LASIK flap creation, intracorneal ring segment implantation, astigmatic keratotomy, presbyopic treatments, and intrastromal lenticule procedures.

METHODS

Literature review.

RESULTS

From its first clinical use in 2001 for LASIK flap creation, femtosecond lasers have steadily made a place as the dominant flap-making technology worldwide. Newer applications are being evaluated and are increasing in their frequency of use.

CONCLUSIONS

Femtosecond laser technology is rapidly becoming a heavily utilized tool in corneal refractive surgical procedures due to its reproducibility, safety, precision, and versatility.

Analysis of corneal endothelial cell density and morphology after laser in situ keratomileusis using two types of femtosecond lasers

Purpose

To compare two different femtosecond lasers used for flap creation during laser-assisted in situ keratomileusis (LASIK) surgery in terms of their effects on the corneal endothelium.

Methods

We performed LASIK surgery on 254 eyes of 131 patients using IntraLase FS60 (Abbott Medical Optics, Inc, Irvine, CA; IntraLase group) and 254 eyes of 136 patients using Femto LDV (Ziemer Group AG, Port, Switzerland; LDV group) for corneal flap creation. The mean cell density, coefficient of variation, and hexagonality of the corneal endothelial cells were determined and the results were statistically compared.

Results

There were no statistically significant differences in the corneal morphology between pre and post LASIK results in each group, nor were there significant differences between the results of both groups at 3 months post LASIK.

Conclusions

Both IntraLase FS60 and Ziemer Femto LDV are able to create flaps without significant adverse effects on the corneal endothelial morphology through 3 months after LASIK surgery.

IntraLase femtosecond laser vs mechanical microkeratomes in LASIK for myopia: a systematic review and meta-analysis

PURPOSE

To evaluate the safety, efficacy, and predictability of IntraLase (Abbott Medical Optics) femtosecond laser-assisted compared to microkeratome-assisted myopic LASIK.

METHODS

A comprehensive literature search of Cochrane Library, PubMed, and EMBASE was conducted to identify relevant trials comparing LASIK with IntraLase femtosecond laser to LASIK with microkeratomes for the correction of myopia. Meta-analyses were performed on the primary outcomes (loss of ≥2 lines of corrected distance visual acuity [CDVA], uncorrected distance visual acuity [UDVA] 20/20 or better, manifest refraction spherical equivalent [MRSE] within ±0.50 diopters [D], final refractive SE, and astigmatism), and secondary outcomes (flap thickness predictability, changes in higher order aberrations [HOAs], and complications).

RESULTS

Fifteen articles describing a total of 3679 eyes were identified. No significant differences were identified between the two groups in regards to a loss of ≥2 lines of CDVA (P=.44), patients achieving UDVA 20/20 or better (P=.24), final UDVA (P=.12), final mean refractive SE (P=.74), final astigmatism (P=.27), or changes in HOAs. The IntraLase group had more patients who were within ±0.50 D of target refraction (P=.05) compared to the microkeratome group, and flap thickness was more predictable in the IntraLase group (P<.0001). The microkeratome group had more epithelial defects (P=.04), whereas the IntraLase group had more cases of diffuse lamellar keratitis (P=.01).

CONCLUSIONS

According to the available data, LASIK with the IntraLase femtosecond laser offers no significant benefits over LASIK with microkeratomes in regards to safety and efficacy, but has potential advantages in predictability.

Analysis of microkeratome thin flap architecture using Fourier-domain optical coherence tomography

PURPOSE

To assess the corneal architecture and reproducibility of LASIK flap thickness created by the Amadeus II mechanical microkeratome (Ziemer Ophthalmic Systems AG) using Fourier-domain optical coherence tomography (OCT; Optovue Inc).

METHODS

Anterior segment Fourier-domain OCT was used to analyze the morphology of 58 LASIK flaps from 30 patients created with the Amadeus II microkeratome 140-μm head and ML7090CLB blades (Med-Logics Inc) at 2 weeks postoperatively. Flap thickness was assessed at 10 points across the central 6 mm of the cornea (horizontal and vertical meridians). Postoperative central corneal flap thickness measured by Fourier-domain OCT was compared with intraoperative ultrasound pachymetry measurements.

RESULTS

No significant difference was noted between central flap thickness measured by intraoperative pachymetry (107.2 ± 14 μm) and postoperative OCT (111.7 ± 11 μm; P=.07, correlation coefficient=0.86). Fourier-domain OCT measurements demonstrated functionally planar flap architecture (standard deviation [SD] of thickness across the flap=4.9 μm, SD range across the flap=2 to 9 μm) for the microkeratome flaps.

CONCLUSIONS

The Amadeus II microkeratome with Med-Logics blades created thin, reproducible, functionally planar flaps as measured by Fourier-domain OCT. Central flap thickness measured by intraoperative ultrasound pachymetry was equivalent to that measured 2 weeks postoperatively by OCT.