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

Myopic LASIK Outcomes: Comparison of Three Different Femtosecond Lasers and a Mechanical Microkeratome Using the Same Excimer Laser

INTRODUCTION

To compare the influence of one microkeratome and three femtosecond lasers on myopic laser in situ keratomileusis (LASIK) outcomes.

METHODS

Retrospective, observational cohort study. We compared 134 eyes treated with the IntraLase 60 kHz, 112 eyes treated with the Femto LDV Z6, 206 eyes treated with the FS200, and 98 eyes treated with the Hansatome zero compression microkeratome. All eyes were operated on using the same surgical protocol with the same excimer laser (Wavelight Allegretto) and were allocated to refraction-matched groups.

RESULTS

One day and one week postoperatively, uncorrected distance visual acuity was significantly lower in the FS200 group compared to others (P = 0.0001). This difference disappeared at the 1- and 3-month postoperative visits. Significant differences were found among groups in terms of safety index (P = 0.0001), residual sphere (P = 0.0001), and residual cylinder (P = 0.02) at the 3-month postoperative visit. No significant differences were found in corrected distance visual acuity or efficacy index.

CONCLUSION

According to our results, a slight delay in visual restoration after FS200 LASIK surgery might be expected. This delay was statistically significant at 1 day and 1 week postoperatively, but there were no differences from the 1-month visit onwards. Additionally, significant differences were found among devices in terms of safety index and the refractive results, which were found not to be clinically relevant.

The 25th Anniversary of Laser Vision Correction in the United States

Laser Vision Correction (LVC) is an elective, self-pay and safe surgical procedure to correct myopia and hyperopia. Since FDA approval 25 years ago, there have been a progression of technological improvements leading to better outcomes and LVC is now one of the safest surgical procedures. With a potential pool of 50 million patients, 6000 trained ophthalmic surgeons regularly treating in over 1000 centers of which 65% are physician owned. Treatments remain low from an earlier peak of 1.4 million to less than 800,000 over last 10 years. The factors preventing patients undergoing surgery have not changed and include the cost of $2000 ± $1000 per eye and fear of laser surgery on their eyes. The latter is overcome by word of mouth referrals and positive social media messaging. In addition, press misinformation and lack of optometrists participating in co-management have not helped grow LVC procedures despite the positive results of the FDA’s Patient Reported Outcomes with LASIK studies known as PROWL. The surgery is quick, and patients can be “in and out” in less than two hours with a rapid recovery, minimal postoperative restrictions and within 24 hours have 20/20 vision. Volume and price drives center and physician profitability with a scheduling capacity of two to four patients’ treatments per hour. Laser vision correction and especially LASIK, remains the treatment of choice for myopic and hyperopic patients wanting to remove their dependency on glasses and contact lenses.

Incidence and predisposing factors of anterior chamber gas bubbles during femtosecond laser flap creation

AIM

To investigate the incidence and the predisposing factors of anterior chamber (AC) gas bubbles during femtosecond laser (FS) flap creation for laser in situ keratomileusis (LASIK).

METHODS

All patients who underwent FS-LASIK surgery at CMU LASIK Center between January 2013 and May 2016 were retrospective reviewed. Preoperative and intraoperative data including keratometry, white-to-white (WTW) corneal diameter, flap parameters (diameter, thickness, hinge position, and tunnel length) and pulse energy were reviewed and compared between incident group and control group. To determine the risk factors, univariate and multivariate conditional logistic regression were used; the eye was unit of analysis.

RESULTS

The incidence of AC gas bubbles was 1.6% (22 out of 1378 eyes). The median WTW in the AC bubbles group was 11.5 mm (range 11.1-12.1), which was significantly different from the control group (11.7 mm, range 10.5-12.8, P=0.021). The result of the median WTW minus the flap diameter in the AC bubbles group was 2.5 mm (range 2.1-3.2), which was statistically different to the control group (2.7 mm, range 1.5-3.8, P=0.008). The logistic regression analysis showed that the result of the WTW minus the flap diameter in the AC bubbles group had an adjusted odds ratio of 0.204 (95%CI; 0.056-0.747, P=0.016).

CONCLUSION

Development of AC gas bubbles during FS flap creation is not an uncommon event in Asian eyes which typically have a small WTW. The flap diameter when adjusted relatively to the WTW is a predisposing factor to the possibility of AC gas bubbles occurrence.

Comparison of visual outcomes after femtosecond laser-assisted LASIK versus flap-off epipolis LASIK for myopia

Background

This study clinically evaluated the visual outcomes after refractive surgery for myopia using femtosecond laser-assisted in situ keratomileusis (femto-LASIK) and flap-off epipolis LASIK (epi-LASIK).

Methods

In this retrospective case series study, 40 eyes of 27 patients were divided into two groups depending on the technique used for refractive surgery. Femto-LASIK and flap-off epi-LASIK flaps were created using femtosecond laser and Epi-K™ epikeratome, respectively. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity, manifest refraction, corneal asphericity, and corneal higher-order aberrations (HOAs) were assessed pre- and postoperatively.

Results

The improvement in logarithm of the minimum angle of resolution (logMAR) UDVA after refractive surgery was statistically significant for both groups (P < 0.001 for all groups); it was significant better in UDVA in femto-LASIK than flap-off epi-LASIK, 0.03 ± 0.06 logMAR (femto-LASIK) and 0.54 ± 0.31 logMAR (flap-off epi-LASIK), at 1 day postoperatively; 0.02 ± 0.05 logMAR (femto-LASIK) and 0.14 ± 0.13 logMAR (flap-off epi-LASIK), at 1 week postoperatively (P < 0.001 and P = 0.019). With regard to the corneal HOAs, the increment in spherical aberration (Z_4,0) was greater in flap-off epi-LASIK than femto-LASIK: 0.626 ± 0.232 μm and 0.479 ± 0.139 μm in the front cornea; 0.556 ± 0.227 μm and 0.430 ± 0.137 μm in the total cornea (P = 0.016 and P = 0.017). However, the back corneal HOA changes did not have a significant effect on the total corneal HOA changes.

Conclusion

Femto-LASIK yielded better early visual outcomes than did flap-off epi-LASIK, but there was no significant difference between the outcomes of the two procedures, 1 week postoperatively.

Laser-assisted in-situ keratomileusis (LASIK) with a mechanical microkeratome compared to LASIK with a femtosecond laser for LASIK in adults with myopia or myopic astigmatism

BACKGROUND

Laser-assisted in-situ keratomileusis (LASIK) is a surgical procedure that corrects refractive errors. This technique creates a flap of the outermost parts of the cornea (epithelium, bowman layer, and anterior stroma) to expose the middle part of the cornea (stromal bed) and reshape it with excimer laser using photoablation. The flaps can be created by a mechanical microkeratome or a femtosecond laser.

OBJECTIVES

To compare the effectiveness and safety of mechanical microkeratome versus femtosecond laser in LASIK for adults with myopia.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2019, Issue 2); Ovid MEDLINE; Embase; PubMed; LILACS; ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We used no date or language restrictions. We searched the reference lists of included trials. We searched the electronic databases on 22 February 2019.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of LASIK with a mechanical microkeratome compared to a femtosecond laser in people aged 18 years or older with more than 0.5 diopters of myopia or myopic astigmatism.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 16 records from 11 trials enrolling 943 adults (1691 eyes) with spherical or spherocylindrical myopia, who were suitable candidates for LASIK. Five hundred and forty-seven participants (824 eyes) received LASIK with a mechanical microkeratome and 588 participants (867 eyes) with a femtosecond laser. Each trial included between nine and 360 participants. In six trials, the same participants received both interventions. Overall, the trials were at an uncertain risk of bias for most domains. At 12 months, data from one trial (42 eyes) indicates no difference in the mean uncorrected visual acuity (logMAR scale) between LASIK with a mechanical microkeratome and LASIK with a femtosecond laser (mean difference (MD) -0.01, 95% confidence interval (CI) -0.06 to 0.04; low-certainty evidence). Similar findings were observed at 12 months after surgery, regarding participants achieving 0.5 diopters within target refraction (risk ratio (RR) 0.97, 95% CI 0.85 to 1.11; 1 trial, 79 eyes; low-certainty evidence) as well as mean spherical equivalent of the refractive error 12 months after surgery (MD 0.09, 95% CI -0.01 to 0.19; 3 trials, 168 eyes [92 participants]; low-certainty evidence). Based on data from three trials (134 eyes, 66 participants), mechanical microkeratome was associated with lower risk of diffuse lamellar keratitis compared with femtosecond laser (RR 0.27, 95% CI 0.10 to 0.78; low-certainty evidence). Thus, diffuse lamellar keratitis was a more common adverse event with femtosecond laser than with mechanical microkeratome, decreasing from an assumed rate of 209 per 1000 people in the femtosecond laser group to 56 per 1000 people in the mechanical microkeratome group. Data from one trial (183 eyes, 183 participants) indicates that dry eye as an adverse event may be more common with mechanical microkeratome than with femtosecond laser, increasing from an assumed rate of 80 per 1000 people in the femtosecond laser group to 457 per 1000 people in the mechanical microkeratome group (RR 5.74, 95% CI 2.92 to 11.29; low-certainty evidence). There was no evidence of a difference between the two groups for corneal haze (RR 0.33, 95% CI 0.01 to 7.96; 1 trial, 43 eyes) and epithelial ingrowth (RR 1.04, 95% CI 0.11 to 9.42; 2 trials, 102 eyes [50 participants]). The certainty of evidence for both outcomes was very low.

AUTHORS' CONCLUSIONS

Regarding the visual acuity outcomes, there may be no difference between LASIK with mechanical microkeratome and LASIK with femtosecond laser. Dry eye and diffuse lamellar keratitis are likely adverse events with mechanical microkeratome and femtosecond laser, respectively. The evidence is uncertain regarding corneal haze and epithelial ingrowth as adverse events of each intervention. The limited number of outcomes reported in the included trials, some with potentially significant risk of bias, makes it difficult to draw a firm conclusion regarding the effectiveness and safety of the interventions investigated in this review.

Treatment of High Astigmatism with WaveLight Allegretto Eye-Q Excimer Laser Platform

Introduction

The WaveLight Allegretto Eye-Q is a flying-spot excimer laser, with a pulse repetition rate of 400Hz, with two galvanometric scanners for positioning laser pulses. The system has an infrared high speed camera operating at 400Hz to track the patient's eye movements that either compensates for changes in eye position or interrupts the treatment if the eye moves outside a preset predetermined range.

Aim

The purpose of this study was to investigate WaveLight Allegretto Eye-Q 400Hz laser delivery platform aimed to correct astigmatism by subjecting the pre and postoperative astigmatic values to vector analysis.

Methods

Patients were divided into two groups, depending on the type of astigmatism. Astigmatism was between 2 and 7 diopters (D). A total of 188 eyes (110 patients), 127 eyes (71 patients) with myopic astigmatism and 61 eyes (39 patients) with mixed astigmatism underwent unremarkable LASIK correction on WaveLight Allegretto Eye-Q 400Hz. The preoperative and postoperative sphere, negative cylinder [C] and axis (ø) of manifest refractions were subjected to vector analysis by calculations of the standard J₀ (cos [4π(ø-90)/360]xC/2) and J₄₅ (sin[4π(ø-90)/ 360]xC/2).

Results

Reporting the key results, we found that J₀ significantly reduced after LASIK (p<0.001) but not J₄₅. There was no significant association between individual pairs of pre and postoperative J₀ &J₄₅ values.

Conclusion

WaveLight Allegretto 400Hz showed excellent results for treating patients with high astigmatism, regardless whether it is mixed or myopic astigmatism. The J₄₅ did not reduce significantly possibly because of the low number of eyes with oblique astigmatism. There was no genuine difference postoperatively between groups treated on WaveLight Allegretto platform according to the vector analyses.

Clinical study on combining femtosecond thin- flap and LASIK with the Triple-A profile for high myopia correction

BACKGROUND

Femtosecond laser-assisted LASIK (FS-LASIK) can make ultra-thin corneal flap accurately. MEL 90 excimer laser provides Triple-A ablation mode, which significantly reduces the amount of corneal tissue cutting. This study aimed to investigate the visual and refractive outcomes in patients with high myopia after thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile.

METHODS

This prospective study included 90 eyes from 90 patients received thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile. According to the pre-operative spherical equivalence (SE), the treated eyes were divided into two groups: the first group (ranged from - 9.0D to - 6.0D) and the second group (ranged from - 11.15D to - 9.0 D). The parameters evaluated pre-operatively and 6 month post-operatively included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, efficacy and safety index, posterior central elevation, and corneal higher-order aberrations (HOAs).

RESULTS

The efficacy indexes were 1.149 ± 0.150 for the first group and 1.173 ± 0.136 for the second group (P > 0.05), whereas safety indexes were 1.135 ± 0.154 and 1.158 ± 0.137 (P > 0.05) respectively. Moreover, 93.8 and 90.6% of patients had an UDVA of 20/20, 51.2 and 49.8% had a UDVA of 20/16 for the first and second groups, respectively; yet, there were no significant differences between both groups at the 20/20 and the 20/16 levels (P > 0.05). 84 and 100% of the firse group patients had a SE within ±0.5 D and ± 1.0 D, and 82 and 100% of the second group patients. There was no significant myopia regression in both groups after 6 months follow-up. At 1, 3 and 6-month after surgery, there were no significant differences in the posterior central elevation between the two groups (P > 0.05). The induction of total HOAs, spherical aberration, and horizontal coma in the first group were significantly less than that in the second group at the 6- month follow-up (P < 0.05), while the differences of the RMS value of vertical coma between both groups were not significant (P > 0.05). The ablation was significantly associated with the post-operative increase in total HOAs, spherical aberration and horizontal coma (P < 0.05),but not with vertical coma (P > 0.05).

CONCLUSION

Our results indicate that using the Triple-A ablation profile of the MEL 90 excimer laser associated with thin-flap is a safe, efficient, and predictable method to correct SE up to - 11.15D. However, for patients with high myopia, under the premise of ensuring a certain optical zone diameter, the ablation depth should be minimized to reduce the increase of the post-operative HOAs so as to improve the visual quality.

Visumax femtolasik versus Moria M2 microkeratome in mild to moderate myopia: efficacy, safety, predictability, aberrometric changes and flap thickness predictability

Introduction

This is an interventional prospective clinical study which was conducted to evaluate the efficacy, safety, predictability, ocular aberrations, and flap thickness predictability of Visumax femtosecond laser (FSL) compared to Moria M2 microkeratome (MK) in mild to moderate myopia.

Methods

This study included 60 eyes who were divided into two groups. Thirty eyes in group (I) in which the flap was created with Visumax FSL, while in group II (30 eyes) the Moria M2 MK was used. Keratometric, refractive, and aberrometric measurements were compared preoperatively and 3 months postoperatively. The intraoperative subtraction pachymetry (the SP 100 Handy pachymeter (Tomey, Nagoya, Japan) was used for preoperative pachymetry and flap thickness measurement.

Results

No significant difference was found between the two groups in regards to postoperative manifest sphere, spherical equivalent, astigmatism, safety indices nor ocular aberrations. Twenty six eyes (86.6%) in group I and 23 eyes in group II (76.6%) were within ±0.5D of the intended correction and 23 eyes (76.6%) in group I and 15 eyes in group II (50%) were within ±0.25D of the intended correction. In group I, the mean postoperative actual flap thickness was 100.12 ± 16.1 μm (81 to 122 μm), while in group II, it was 104.6 ± 20.1 μm (62 to 155 μm). The difference was statistically significant (p = 0.001).

Conclusions

Both Visumax and Moria M2 MK are safe and effective in treating myopia with no statistically significant difference in induction of ocular aberrations but with potential advantage for Visumax regarding predictability. More accurate flap thickness is achieved with Visumax femtolasik.

Trial registration

This study was retrospectively registered on 19/6/2017. Trial registration number NCT03193411, clinicalTrials.gov.

Recent advances in laser in situ keratomileusis-associated dry eye

Dry eye is the most common complication after laser in situ keratomileusis (LASIK). The major cause of LASIK-associated dry eye is corneal nerve damage. Early identification and treatment of post-operative dry eye are essential to prevent further ocular surface damage. This article reviews the recent studies of LASIK-associated dry eye, including clinical features, aetiology, risk factors, evaluations and treatment. The applications of novel technologies in LASIK-associated dry eye evaluation like anterior segment spectral-domain optical coherence tomography (SD-OCT) and corneal confocal microscopy are also introduced in this review.

Femtosecond-Assisted LASIK Versus PRK: Comparison of 6-Month Visual Acuity and Quality Outcome for High Myopia

OBJECTIVE

To compare the results of femtosecond-assisted laser in situ keratomileusis (femto-LASIK) and photorefractive keratectomy with mitomycin C (PRK-MMC) for the correction of myopia more than 7.0 diopters (D).

METHODS

In this comparative nonrandomized trial, 60 eyes (30 eyes in each group) were enrolled. Patients were tested for uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent, ocular and corneal aberrations, and contrast sensitivity (CS) before surgery and at 3 and 6 months postoperatively.

RESULTS

Mean preoperative myopia was -8.65±1.51 and -8.04±1.70 D in the femto-LASIK and PRK-MMC groups, respectively (P=0.149). Intergroup differences in baseline indices were not statistically significant. At 6 months after surgery, UDVA showed an improving trend, but it was better in the femto-LASIK group (P=0.026). CDVA in the two groups remained similarly unchanged (P=0.170). For the femto-LASIK and PRK-MMC groups, the safety indices were 1.01±0.05 and 1.01±0.14 (P=0.949), respectively, and the efficacy indices were 0.99±0.07 and 0.93±0.22 (P=0.192), respectively. Comparing CS, only CS18 showed a significantly greater decrease in the femto-LASIK group compared with the PRK-MMC group (P=0.016). Intergroup differences were not statistically significant in other spatial frequencies. Changes in the ocular and corneal higher order aberrations were not statistically different between the two groups except ocular coma, which increased in the femto-LASIK group (P=0.041).

CONCLUSION

Femto-LASIK improves UDVA better than PRK-MMC in high myopia. However, because of increased coma, the quality of vision is reduced. In other words, visual acuity outcome is better with femto-LASIK and visual quality outcome is better with PRK-MMC.

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.

Hyperopic laser in situ keratomileusis: comparison of femtosecond laser and mechanical microkeratome flap creation

PURPOSE

To evaluate and compare the refractive predictability and stability of laser in situ keratomileusis (LASIK) flap creation performed with a femtosecond laser and with a mechanical microkeratome to correct mild to moderate hyperopia.

SETTING

American University of Beirut Medical Center, Beirut, Lebanon.

DESIGN

Retrospective case series.

METHODS

Patients who had hyperopic LASIK treatment using the Amaris excimer laser were included. Eyes in which the LDV femtosecond laser was used for flap creation were compared with eyes in which the Moria M2 microkeratome was used.

RESULTS

The microkeratome group comprised 53 eyes and the femtosecond laser group, 72 eyes. Baseline characteristics were similar between groups (P > .05). The mean spherical equivalent (SE) deviation from target 1 week postoperatively was -0.08 diopter (D) ± 0.58 (SD) in the femtosecond laser group and -0.06 ± 0.87 D in the microkeratome group (P = .92). Thereafter, the mean SE deviation from target increased gradually and by 6 months postoperatively was +0.30 ± 0.50 D and +0.70 ± 0.71 D, respectively (P = .001). The correlation between the achieved and the attempted SE refraction was better in the femtosecond laser group (R(2) = 0.806) than the microkeratome group (R(2) = 0.671).

CONCLUSIONS

Using the same nomogram, the short-term refractive outcomes of hyperopic LASIK with flap creation performed with the femtosecond laser were comparable to those for the microkeratome; however, the femtosecond group showed significantly better stability over the 6-month follow-up and better predictability, as reflected by a lower standard deviation and stronger Pearson correlation.

FINANCIAL DISCLOSURE

Dr. Arba Mosquera is an employee of Schwind eye-tech-solutions GmbH and Co. KG. No other author has a financial or proprietary interest in any material or method mentioned.

Comparison of the femtosecond laser and mechanical microkeratome for flap cutting in LASIK

AIM

To compare refractive results, higher-order aberrations (HOAs), contrast sensitivity and dry eye after laser in situ keratomileusis (LASIK) performed with a femtosecond laser versus a mechanical microkeratome for myopia and astigmatism.

METHODS

In this prospective, non-randomized study, 120 eyes with myopia received a LASIK surgery with the VisuMax femtosecond laser for flap cutting, and 120 eyes received a conventional LASIK surgery with a mechanical microkeratome. Flap thickness, visual acuity, manifest refraction, contrast sensitivity function (CSF) curves, HOAs and dry-eye were measured at 1wk; 1, 3, 6mo after surgery.

RESULTS

At 6mo postoperatively, the mean central flap thickness in femtosecond laser procedure was 113.05±5.89 µm (attempted thickness 110 µm), and 148.36±21.24 µm (attempted thickness 140 µm) in mechanical microkeratome procedure. An uncorrected distance visual acuity (UDVA) of 4.9 or better was obtained in more than 98% of eyes treated by both methods, a gain in logMAR lines of corrected distance visual acuity (CDVA) occurred in more than 70% of eyes treated by both methods, and no eye lost ≥1 lines of CDVA in both groups. The difference of the mean UDVA and CDVA between two groups at any time post-surgery were not statistically significant (P>0.05). The postoperative changes of spherical equivalent occurred markedly during the first month in both groups. The total root mean square values of HOAs and spherical aberrations in the femtosecond treated eyes were markedly less than those in the microkeratome treated eyes during 6mo visit after surgery (P<0.01). The CSF values of the femtosecond treated eyes were also higher than those of the microkeratome treated eyes at all space frequency (P<0.01). The mean ocular surface disease index scores in both groups were increased at 1wk, and recovered to preoperative level at 1mo after surgery. The mean tear breakup time (TBUT) of the femtosecond treated eyes were markedly longer than those of the microkeratome treated eyes at postoperative 1, 3mo (P<0.01).

CONCLUSION

Both the femtosecond laser and the mechanical microkeratome for LASIK flap cutting are safe and effective to correct myopia, with no statistically significant difference in the UDVA, CDVA during 6mo follow-up. Refractive results remained stable after 1mo post-operation for both groups. The femtosecond laser may have advantages over the microkeratome in the flap thickness predictability, fewer induced HOAs, better CSF, and longer TBUT.

Higher Order Aberrations and Visual Outcomes in Wavefront-Optimized Sub-Bowman Keratomileusis: Flap Creation Using Femtosecond Laser Versus Mechanical Microkeratome

PURPOSE

The aim of this study was to compare the outcomes of wavefront-optimized sub-Bowman keratomileusis (SBK) performed using the 150 KHz IntraLase femtosecond (IFS) laser (Abbot Medical Optics) with those using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome (Moria SA).

DESIGN

A prospective comparative clinical trial.

METHODS

Fifty patients had bilateral wavefront-optimized SBK performed for myopia or myopic astigmatism. In 25 patients, the flap was created with the 150 KHz IFS laser (group 1) and in the other 25 with the Moria One Use-Plus SBK mechanical microkeratome (group 2). All other treatment parameters were the same. Results were reported for 1 eye per patient in each group (ie, 25 eyes in each group).

RESULTS

Efficacy, refractive stability, predictability, and safety profiles were comparable between the 2 groups. Although higher order aberrations (HOAs) increased significantly in both groups after laser in situ keratomileusis, intergroup comparison revealed that group 1 was associated with a significantly higher induction of both total HOAs [mean root mean square (RMS), 0.63 ± 0.20 in group 1 vs 0.52 ± 0.14 in group 2; P = 0.031] and spherical aberrations (RMS, 0.37 ± 0.17 in group 1 vs 0.22 ± 0.09 in group 2; P < 0.001) as compared with group 2.

CONCLUSIONS

Flaps created using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome were associated with significantly lower induction of total HOAs and spherical aberrations as compared with 150 KHz IFS flaps at the end of 3 months follow-up.

Effect of Myopic Defocus on Visual Acuity after Phakic Intraocular Lens Implantation and Wavefront-guided Laser in Situ Keratomileusis

This study aimed to investigate the effect of myopic defocus on visual acuity after phakic intraocular lens (IOL) implantation and wavefront-guided laser in situ keratomileusis (wfg-LASIK). Our prospective study comprised thirty eyes undergoing posterior chamber phakic IOL implantation and 30 eyes undergoing wfg-LASIK. We randomly measured visual acuity under myopic defocus after cycloplegic and non-cycloplegic correction. We also calculated the modulation transfer function by optical simulation and estimated visual acuity from Campbell &Green's retinal threshold curve. Visual acuity in the phakic IOL group was significantly better than that in the wfg-LASIK group at myopic defocus levels of 0, -1, and -2 D (p < 0.001, p < 0.001, and p = 0.02, Mann-Whitney U-test), but not at a defocus of -3 D (p = 0.30). Similar results were also obtained in a cycloplegic condition. Decimal visual acuity values at a myopic defocus of 0, -1, -2, and -3 D by optical simulation were estimated to be 1.95, 1.21, 0.97, and 0.75 in the phakic IOL group, and 1.39, 1.11, 0.94, and 0.71 in the wfg-LASIK group, respectively. From clinical and optical viewpoints, phakic IOL implantation was superior to wfg-LASIK in terms of the postoperative visual performance, even in the presence of low to moderate myopic regression.

Flap characteristics, predictability, and safety of the Ziemer FEMTO LDV femtosecond laser with the disposable suction ring for LASIK

AIMS

The outcomes of laser-assisted in situ keratomileusis (LASIK) operations performed with the Classic FEMTO LDV femtosecond laser using the plastic single-use suction ring (Ziemer Ophthalmic Systems) and the Allegretto Wave Concerto 500 Hz excimer laser (Wavelight AG) are presented in terms of accuracy, predictability, and safety of the operation.

METHODS

A FEMTO LDV plastic suction ring was used for flap creation in 342 eyes of 179 patients. The intended flap thickness was 90 μm. The size of the suction ring varied from 9.0 to 10.0 mm. Flap dimensions were measured and correlated to preoperative characteristics.

RESULTS

Mean flap thickness was very constant, 89.6 ± 2.0 μm (range 84-97). In 163 bilateral operations, the second flap was 1.1 μm thinner than the one cut first (P<0.0001). Mean flap diameter was 9.4 ± 0.2 mm (range 8.1-9.9). Mean hinge length was 3.9 ± 0.2 mm (range 3.0-4.2). In hyperopic eyes, flap thickness correlated negatively with keratometric power K1 and flap diameter. In hyperopic eyes, flap diameter correlated positively with spherical equivalent refraction and with keratometric power K1 as well as hinge length both in myopic and hyperopic eyes. Complications were reported in 12 (3.5%) eyes. Complications were very mild and none of them prevented further refractive laser treatment. Two Snellen lines of corrected distance visual acuity were lost in one (0.3%) eye.

CONCLUSION

The FEMTO LDV plastic single-use suction rings yielded accurate and reproducible flaps and were safe for the creation of thin corneal flaps.

Comparative study of visual acuity and aberrations after intralase femtosecond LASIK: small corneal flap versus big corneal flap

AIM

To study the effect of different flap sizes on visual acuity, refractive outcomes, and aberrations after femtosecond laser for laser in situ keratomileusis (LASIK).

METHODS

In each of the forty patients enrolled, 1 eye was randomly assigned to receive treatment with a 8.1mm diameter corneal flap, defined as the small flap, while the other eye was treated with a 8.6mm diameter corneal flap, defined as the big flap. Refractive errors, visual acuity, and higher-order aberrations were compared between the two groups at week 1, month 1 and 3 postoperatively.

RESULTS

The postoperative refractive errors and visual acuity all conformed to the intended goal. Postoperative higher-order aberrations were increased, especially in spherical aberration (Z12) and vertical coma (Z7). There were no statistically significant differences between the two groups in terms of postoperative refractive errors, visual acuity, root mean square of total HOAs (HO-RMS), trefoil 30° (Z6), vertical coma (Z7), horizontal coma (Z8), trefoil 0° (Z9), and spherical aberration (Z12) at any point during the postoperative follow-up.

CONCLUSION

Both the small and big flaps are safe and effective procedures to correct myopia, provided the exposure stroma meets the excimer laser ablations. The personalized size corneal flap is feasible, as we can design the size of corneal flap based on the principle that the corneal flap diameter should be equal to or greater than the sum of the maximum ablation diameter and apparatus error.

Comparison of Ziemer FEMTO LDV "Classic" and "Crystal Line" femtosecond laser flap quality by Fourier-domain optical coherence tomography

AIM

To compare the regularity and accuracy of laser in situ keratomileusis (LASIK) flaps created by the Ziemer FEMTO LDV "Classic" (Ziemer "Classic") and Ziemer FEMTO LDV Crystal Line femtosecond laser (Ziemer Crystal Line).

METHODS

Fourier-domain optical coherence tomography (RTVue OCT) was used to measure the morphology of 200 LASIK flaps of 100 consecutive patients created with the Ziemer Classic (100 flaps) or the Ziemer Crystal Line (100 flaps) at one week postoperatively. Flap thickness was evaluated at 36 specified measurement points on each flap. For all procedures with both lasers, the nominal flap thickness was 110µm.

RESULTS

The mean flap thickness of the Ziemer Crystal Line group (102.49±2.68µm) was thinner than that of the Ziemer Classic group (107.65±5.09µm) (P<0.01). Average thickness of all flaps was uniform within 4µm at all measurement points. The flaps in the Ziemer Crystal Line group were more regular than those in the Ziemer Classic group when measured from the center to the periphery. The maximum deviation from the nominal 110µm of 36 measurements was 8µm in the Ziemer Classic group, while in the Ziemer Crystal Line group it was 9µm. Within the 3 600 measurements on the 100 eyes, differences greater than 20µm were observed 0.14% in the Ziemer Classic group, and 0.04% in the Ziemer Crystal Line group.

CONCLUSION

The flaps created with the Ziemer FEMTO LDV Crystal Line femtosecond laser are more uniform and thinner than those created by the Ziemer FEMTO LDV Classic femtosecond laser.

The role of corneal innervation in LASIK-induced neuropathic dry eye

Almost half the patients who undergo laser in situ keratomileusis (LASIK) experience dry eye following the procedure. However, the etiology of LASIK-induced dry eye is unclear. The purpose of this review is to examine and summarize the current evidence for the etiology of LASIK-induced dry eye, with a focus on ocular surface sensitivity and corneal innervation. Evidence suggests that the alteration of corneal nerves after LASIK is the most likely cause of the subjective symptoms of LASIK-induced dry eye, even though corneal sensitivity and the clinical indicators of dry eye return to apparently normal values within a year due to the partial recovery of the corneal nerve plexus. The hypothesis is explored that dry eye symptoms following LASIK may result from abnormal sensation due to LASIK-induced corneal neuropathy. Other factors, such as alterations in conjunctival goblet cell density, might also contribute to the symptoms and signs of LASIK-induced dry eye. Inter-relationships between nerve morphology, tear neuropeptide levels and dry eye require further investigation. A better understanding of this phenomenon may result in improved management of post-LASIK dry eye.

Comparison of LASEK, mechanical microkeratome LASIK and Femtosecond LASIK in low and moderate myopia

PURPOSE

We conducted a prospective study to determine the best treatment option for patients with low-to-moderate spherical myopia or myopic astigmatism who are considered equally eligible for LASEK with mitomycin-C (MMC) and LASIK with either mechanical microkeratome or femtosecond laser flap creation.

METHODS

Forty-six adult patients (86 eyes) who underwent LASEK with MMC (16 patients, 31 eyes), and mechanical microkeratome LASIK (13 patients, 23 eyes) or Femtosecond LASIK (17 patients, 32 eyes) were assessed for clinical outcomes 1, 3 and 6 months post-operatively.

RESULTS

Six months after surgery, all eyes in all three groups were within 1 D of the intended refractive change. UCVA 20/20 or better was achieved in 96% of eyes undergoing LASEK with MMC 88% of eyes in the mechanical microkeratome LASIK and 72% of eyes in the Femtosecond LASIK group at 6 months. Mean spherical equivalent was -0.12 ± 0.22 D, -0.09 ± 0.28 D and -0.25 ± 0.28 D in the three groups, respectively (p = 0.077). Patients in the LASEK with MMC group had less high order aberrations at 3 and 6 months compared to the two LASIK groups. None of the three procedures were associated with early- or late-onset complications or loss of 2 or more lines after surgery.

CONCLUSIONS

After an initially slower visual improvement, LASEK with MMC, and to lesser extent, LASIK with mechanical microkeratome, produced better visual acuity and less corneal aberrations compared to Femtosecond LASIK at 3 and 6 months after surgery. These observations deserve further investigation in a randomized controlled trial.

Lower energy to make a corneal flap with a 60 kHz femtosecond laser reduces flap inflammation and corneal stromal cell death but weakens flap adhesion

Purpose

To compare corneal flaps created in rabbits with a 60 kHz femtosecond (FS) laser using different levels of raster energy and to measure early inflammation, corneal stromal cell death, and late postoperative adhesion strength.

Methods

Sixty rabbits were divided into three groups of 20 each. A flap 110 µm thick and 9.0 mm in diameter was made in one eye of each rabbit at raster energies of 0.7 µJ, 1.1 µJ, and 2.4 µJ. Histopathological evaluation for inflammation and apoptosis using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed at 4 and 24 hours after flap creation. The adhesion strength of the flaps was measured with a tension meter at 1 and 3 months.

Results

Twenty four hours after flap creation, the 2.4 µJ group had more inflammatory and CD11b-positive cells than the 0.7 and 1.1 µJ groups. The number of TUNEL-positive cells increased with raster energy at 4 and 24 hours. The grams of force (gf) needed to detach the flaps at 3 months was significantly higher in 2.4 µJ group (170 gf) than in 0.7 µJ group (97.5 gf) and 1.1 µJ group (100 gf, p = 0.03).

Conclusions

Using raster energy lower than 1.1 µJ to make a flap with a 60 kHz FS laser decreases inflammatory cell infiltration and corneal stromal cell death in the central cornea but may result in a weaker flap than using higher raster energy (2.4 µJ).

Femtosecond lasers for LASIK flap creation: a report by the American Academy of Ophthalmology

OBJECTIVE

To review the published literature to assess the safety, efficacy, and predictability of femtosecond lasers for the creation of corneal flaps for LASIK; to assess the reported outcomes of LASIK when femtosecond lasers are used to create corneal flaps; and to compare the differences in outcomes between femtosecond lasers and mechanical microkeratomes.

METHODS

Literature searches of the PubMed and Cochrane Library databases were last conducted on October 12, 2011, without language or date limitations. The searches retrieved a total of 636 references. Of these, panel members selected 58 articles that they considered to be of high or medium clinical relevance, and the panel methodologist rated each article according to the strength of evidence. Four studies were rated as level I evidence, 14 studies were rated as level II evidence, and the remaining studies were rated as level III evidence.

RESULTS

The majority of published studies evaluated a single laser platform. Flap reproducibility varied by device and the generation of the device. Standard deviations in flap thicknesses ranged from 4 to 18.4 μm. Visual acuities and complications reported with LASIK flaps created using femtosecond lasers are within Food and Drug Administration safety and efficacy limits. Of all complications, diffuse lamellar keratitis is the most common after surgery but is generally mild and self-limited. Corneal sensation was reported to normalize by 1 year after surgery. Unique complications of femtosecond lasers included transient light-sensitivity syndrome, rainbow glare, opaque bubble layer, epithelial breakthrough of gas bubbles, and gas bubbles within the anterior chamber.

CONCLUSIONS

Available evidence (levels I and II) indicates that femtosecond lasers are efficacious devices for creating LASIK flaps, with accompanying good visual results. Overall, femtosecond lasers were found to be as good as or better than mechanical microkeratomes for creating LASIK flaps. There are unique complications that can occur with femtosecond lasers, and long-term follow-up is needed to evaluate the technology fully.

Smoothness assessment of corneal stromal surfaces

PURPOSE

To assess the accuracy of the scanning electron microscopy (SEM) and present alternative approaches to quantify surface roughness based on numerical analysis.

SETTING

Department of Ophthalmology, Maisonneuve-Rosemont Hospital, University of Montreal, Montreal, Quebec, Canada.

DESIGN

Experimental study.

METHODS

Lamellar stromal cuts were performed on human corneas using a femtosecond laser or a microkeratome. The photodisrupted stromal surfaces were processed for SEM, and images were acquired at ×1000 magnification. First, images were evaluated by independent observers. Second, images were analyzed based on first-order and second-order statistics of gray-level intensities. Third, 3-dimensional (3-D) surface reconstructions were generated from pairs of SEM images acquired at 2 angles.

RESULTS

Results show that traditional assessment of roughness based on evaluating SEM images by independent observers can be replaced by computer-image texture analysis; an algorithm was developed to avoid subjective and time-consuming observations. The 3-D reconstructions allowed additional characterization of surface properties that was not possible with SEM images alone. Significant fluctuations in surface height were lost, although they could be retrieved using 3-D reconstructions.

CONCLUSIONS

Image texture analysis allowed objective and repeatable assessment of stromal surface roughness; however, full assessments of surface-height fluctuations required 3-D reconstruction. These complementary methodologies offer a more comprehensive assessment of corneal surface roughness in clinical applications.

Optimal parameters to improve the interface quality of the flap bed in femtosecond laser-assisted laser in situ keratomileusis

PURPOSE

To analyze the interface quality of the anterior stroma after femtosecond laser flap creation using atomic force microscopy.

SETTING

IRCCS Fondazione G.B. Bietti, Rome, Italy.

DESIGN

Experimental study.

METHODS

A 110 μm depth flap was created in 20 human corneal tissues using a femtosecond laser platform (Intralase iFS). Tissues were divided into 4 groups of various cutting parameters: pulse energy and spot separation of 0.75 μJ and 6 μm (Group 1), 0.65 μJ and 5 μm (Group 2), 0.55 μJ and 4 μm (Group 3), and 0.45 μJ and 4 μm (Group 4). Four additional tissue sections were cut using a motorized microkeratome (Hansatome). Atomic force microscopy (Autoprobe CP) analysis was performed on the stromal bed of each sample.

RESULTS

The corneal tissues treated with higher pulse energies and wider spot separations (Groups 1 and 2) showed a rougher stromal bed interface (root mean square [RMS] rough = 0.23 μm ± 0.008 (SD) and 0.24 ± 0.009 μm, respectively) than tissues in Groups 3 and 4 (RMS rough = 0.18 ± 0.006 μm and 0.18 ± 0.008 μm, respectively; P<.001, 1-way analysis of variance). The stromal surface quality of tissues treated with pulse energies of 0.55 μJ or lower and 4 μm spot separation compared favorably with that of tissues cut by the microkeratome (RMS rough = 0.17 ± 0.006 μm; P>.05, Tukey).

CONCLUSIONS

The femtosecond stromal interface quality was improved with pulse energy lower and spot separations narrower than those currently used in the clinical setting. The flap interface smoothness created by the femtosecond laser was comparable to that created by the microkeratome.

FINANCIAL DISCLOSURE

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

Laser in situ keratomileusis enhancements with the Ziemer FEMTO LDV femtosecond laser following previous LASIK treatments

BACKGROUND

The aim of this paper is to present the accuracy, predictability, and safety outcomes of LASIK enhancements performed with the FEMTO LDV femtosecond laser (Ziemer Ophthalmic Systems, Port, Switzerland) and the Allegretto Wave Concerto 500 Hz excimer laser (Wavelight AG, Erlangen, Germany), following previous LASIK treatments.

METHODS

FEMTO LDV was used for flap creation in 85 previously LASIK-treated eyes of 62 patients. The intended flap thickness was 90 μm in 81 eyes and 140 μm in 4 eyes. The size of the suction ring was 9.0 mm in 72 eyes and 9.5 mm in 13 eyes. Flap dimensions were measured and correlated to preoperative characteristics.

RESULTS

With the intended flap thickness of 90 μm in previously LASIK-treated eyes, the actual flap thickness was 90.2 ± 6.6 μm (range 80-122), and the flap diameter was 9.2 ± 0.2 mm (range 8.7-9.9). The mean hinge length was 4.0 ± 0.2 mm (range 3.0-4.8). Flap thickness correlated positively with patient age and hinge length. Complications were reported in 12 eyes (14.1 %). Most of the complications were very mild, and none of them prevented further refractive laser treatment. One eye lost two Snellen lines of best spectacle-corrected visual acuity.

CONCLUSIONS

Femtosecond LASIK enhancement is warranted only in rare cases. Surgical experience is needed and special caution must be practiced. For cases of a primary free cap, femtosecond LASIK is not recommended.

The effect of hinge location on corneal sensation and dry eye after LASIK: a systematic review and meta-analysis

BACKGROUND

The aim of this meta-analysis is to investigate the possible effect of hinge location on corneal sensation and dry eye syndrome after laser-assisted in situ keratomileusis (LASIK).

METHODS

A comprehensive literature search was conducted in the PubMed, EMBASE, and Cochrane Controlled Trials Register to identify potentially relevant randomized controlled trials (RCTs) of comparing the effects of horizontal-hinge flaps and vertical-hinge flaps on corneal sensation and dry eye after LASIK. Meta-analyses were performed for corneal sensation, tear break-up time (TBUT), Schirmer's I test and corneal fluorescein staining (CFS) at 1 week, 1, 3, and 6 months postoperatively.

RESULTS

Eight RCTs (657 eyes) investigating the effects of hinge location on the corneal sensation and dry eye syndrome after LASIK were identified. The results showed that the horizontal-hinge group causes less loss of sensation than the vertical-hinge group, and the difference was significant at 3-month postoperative (p = 0.01). The TBUT value was significantly larger and a lower percentage of patients with CFS in the horizontal-hinge group than in the vertical-hinge group at 1-month postoperative (p = 0.007 and p = 0.01, respectively) and 3-month (p = 0.03 and p = 0.009, respectively); Schirmer's I test values were also higher in the horizontal-hinge group, but the difference did not reach statistically significance at each postoperative period.

CONCLUSIONS

According to the available data, we suggest that hinge location may have some effect on corneal sensation and dry eye syndrome after LASIK at the early postoperative period. However, there was no significant difference between the groups at 6 months after surgery. Further well-organized, prospective, randomized studies involving more patients are warranted.

Visual performance after posterior chamber phakic intraocular lens implantation and wavefront-guided laser in situ keratomileusis for low to moderate myopia

PURPOSE

To compare postoperative visual function after implantable collamer lens (ICL) implantation and after wavefront-guided laser in situ keratomileusis (LASIK) in eyes with low to moderate myopia.

DESIGN

Retrospective observational case study.

PATIENTS AND METHODS

We investigated 30 eyes of 20 patients undergoing ICL implantation and 64 eyes of 38 patients undergoing wavefront-guided LASIK for the correction of low to moderate myopia (manifest spherical equivalent: -3.00 to -5.88 diopters [D]). Ocular higher-order aberrations (HOAs) and contrast sensitivity (CS) function were measured by Hartmann-Shack aberrometry and a contrast sensitivity unit before and 3 months after surgery, respectively. From the contrast sensitivity, the area under the log contrast sensitivity function was calculated.

RESULTS

For 4-mm and 6-mm pupils, the changes in ocular third-order aberrations, fourth-order aberrations, and total HOAs after ICL implantation were significantly less than those after wavefront-guided LASIK (P < .05, Mann-Whitney U test). The postoperative area under the log contrast sensitivity function was significantly increased after ICL implantation (P < .001), whereas, after wavefront-guided LASIK, it was not significantly changed (P = .11).

CONCLUSIONS

ICL implantation induces significantly fewer ocular HOAs than wavefront-guided LASIK. Moreover, CS was significantly improved after ICL implantation but unchanged after wavefront-guided LASIK in eyes with low to moderate myopia. Thus, even in the correction of low to moderate myopia, ICL implantation appears to be superior in visual performance to wavefront-guided LASIK, suggesting that it may be a viable surgical option for the treatment of such eyes.

Corneal flap morphological analysis using anterior segment optical coherence tomography in laser in situ keratomileusis with femtosecond lasers versus mechanical microkeratome

AIM

To assess and compare the flap morphology using anterior segment optical coherence tomography (AS-OCT) in laser in situ keratomileusis (LASIK) with Femto LDV femtosecond lasers versus Hansatome mechanical Microkeratome.

METHODS

AS-OCT (Visante) was used to compare 1 month postoperatively the morphology of the flaps created with Femto LDV femtosecond lasers or Hansatome Microkeratome. The intended flap thickness was 110µm and 160µm respectively. The thickness of twenty-five points across each flap, which were 0mm, 1.5mm, 2.5mm, and 3.5mm to the corneal vertex on the horizontal, vertical, 45° and 135° meridian respectively, was evaluated.

RESULTS

One month postoperative, the central flap thickness in the Femto LDV group was 107.43±4.70µm, while 125.90±17.50µm in the Hansatome group. The difference between the actual and the expected flap thickness was 5.61±3.84µm and 31.52±12.27µm, respectively. The Hansatome group had presented a statistically significant result (P<0.001). Flap morphology showed a more regular planar shape in the Femto LDV group and a meniscus shape in the Hansatome group.

CONCLUSION

AS-OCT is a direct and fast procedure to assess the flap morphology. The morphology by AS-OCT showed that the flaps created with Femto LDV femtosecond laser were more accurate and regular than the flaps created with Hansatome microkeratome.

Cellular effects after laser in situ keratomileusis flap formation with femtosecond lasers: a review

PURPOSE

To provide an overview of the cellular effects of femtosecond laser in laser in situ keratomileusis flap formation.

METHODS

Literature review.

RESULTS

The IntraLase is the only femtosecond laser with sufficient histopathological and confocal studies to allow review of the cellular effects of laser application. Histopathological analyses have demonstrated that the energy per pulse and total energy delivered play important roles in the inflammatory reaction to the surgery. The IntraLase laser triggers cellular necrosis (death accompanied by the release of lysosomal enzymes and other components from membrane-bound intracellular compartments) in the corneal stroma surrounding the lamellar cut rather than apoptosis (gentler form of cell death in which most intracellular components remain confined to membrane-bound apoptotic bodies) that is predominant with the microkeratome. Necrosis is a more inflammatory form of cell death that attracts more inflammatory cells. This is likely why earlier femtosecond lasers, such as the 15-kHz IntraLase laser, which requires higher total energy delivery to cut a flap, are associated with more corneal inflammation and diffuse lamellar keratitis. The design of the 60-kHz IntraLase model allows for much lower energy delivery to cut the flap and, therefore, a substantial reduction in keratocyte necrosis to the point that the overall inflammatory response is not significantly different from the microkeratome. Histopathological analysis performed with the Femtec femtosecond laser noted little change in the corneal stromal structure. Confocal microcopy studies performed with the IntraLase laser showed keratocyte "activation" in the stroma and greater fibrotic scarring at the interface than that induced by a mechanical microkeratome.

CONCLUSIONS

The morphologic alterations in the corneal stroma produced by currently available models of the IntraLase laser are comparable to those produced by mechanical microkeratomes. Advances that have resulted in a reduction in the total amount of energy delivered by the laser when it cuts the flap have resulted in a decrease in the inflammatory response associated with femtosecond flap formation to the point that it is indistinguishable from the microkeratome at the cellular level. Further study of each of the femtosecond laser models, including the 150-kHz IntraLase laser, is needed to fully characterize the corneal response to these lasers.

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.

One year follow-up of contrast sensitivity following conventional laser in situ keratomileusis and laser epithelial keratomileusis

PURPOSE

To determine the effect of conventional laser in situ keratomileusis (LASIK) and laser epithelial keratomileusis (LASEK) for myopia on contrast sensitivity (CS) using the Pelli-Robson and Vector Vision CSV-1000E CS tests.

METHODS

A prospective, comparative study was conducted on 36 eyes of 36 patients with myopia undergoing LASIK (18 eyes) and LASEK (18 eyes). Surgery was performed using the Technolas 217z laser (Bausch & Lomb). CS was recorded preoperatively and at 3, 6 and 12 months postoperatively.

RESULTS

No statistically significant difference was found in LogMAR uncorrected visual acuity post-LASIK (-0.02 ± 0.16) and LASEK (-0.04 ± 0.14). Using the Pelli-Robson, CS was significantly lower in the LASIK group 3 and 6 months postoperatively. No significant postoperative reduction in CS was observed in either treatment group. Using the CSV-1000E test, CS was significantly reduced post-LASIK at 3 (p = 0.05) and 6 (p = 0.05) cycles/degree under photopic conditions. No significant postoperative change occurred in the LASEK group under photopic or scotopic conditions. There was no significant difference in postoperative CS between the LASIK and LASEK groups at 3, 6, 12 or 18 cycles/degree using the CSV-1000E test.

CONCLUSION

One year postoperatively, there was no difference in CS between both treatment groups using the Pelli-Robson and CSV-1000E tests. CS was reduced postoperatively in the LASIK group at the lower spatial frequencies under photopic conditions. No postoperative change was detected in CS following LASIK or LASEK using the Pelli-Robson test.

Custom vs conventional PRK: a prospective, randomized, contralateral eye comparison of postoperative visual function

PURPOSE

To determine whether VISX S4 (VISX Inc) custom photorefractive keratectomy (PRK) results in better visual outcomes than VISX S4 conventional PRK.

METHODS

Photorefractive keratectomy was performed on 80 eyes from 40 patients in this randomized, prospective, contralateral eye study. Dominant eyes were randomized to one group with the fellow eye receiving the alternate treatment. Primary outcome measures included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), contrast sensitivity, and root-mean-square (RMS) higher order aberrations.

RESULTS

Mean UDVA was -0.023±0.099 (20/19) in the custom group and -0.044±0.080 (20/18) in the conventional group 6 months after surgery (P=.293). Mean CDVA was -0.073±0.067 (20/17) in the custom group and -0.079±0.071 (20/17) in the conventional group 6 months after surgery (P=.659). Total higher order aberration RMS and spherical aberration increased in both groups compared to preoperative values (P<.05). Coma increased in the conventional group (P<.05) whereas it was similar to preoperative values in the custom group. No significant differences were noted in induction of trefoil.

CONCLUSIONS

Custom and conventional PRK were shown to be safe and effective with excellent visual acuity and contrast sensitivity performance at 6 and 12 months. Conventional PRK induced more coma than custom PRK; however, this did not seem to correlate with clinical outcomes.

Evaluation of LASIK treatment with the Femto LDV in patients with corneal opacity

PURPOSE

To evaluate the relative effectiveness and safety of LASIK using the Femto LDV (Ziemer Ophthalmic Systems AG) and IntraLase FS 60 (Abbott Medical Optics Inc) femtosecond lasers in patients with corneal opacity.

METHODS

Patients with corneal opacity were retrospectively selected between March and July 2009. For this study, 205 eyes with 90-μm corneal flaps created using the Femto LDV (LDV group) and 200 eyes with corneal flaps created using the IntraLase FS 60 (Intra-Lase group) were selected. The flap thickness of the IntraLase group was determined by observation with slit-lamp microscopy. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction spherical equivalent (MRSE) were measured pre- and postoperatively and were statistically evaluated using the Student t test and Mann-Whitney U-test.

RESULTS

Regardless of the levels of opacity, eyes in the LDV group experienced uneventful procedures with no complications. Eyes in the IntraLase group had corneal flaps of 100- to 130-μm thickness and uneventful procedures; however, gas breakthrough was observed in 27 eyes. Of all eyes, 117 eyes from the LDV group and 109 eyes from the IntraLase group were available for 3-month follow-up. Mean 3-month postoperative UDVA, CDVA, and MRSE for the LDV group were 20/12.5, 20/12.5, and 0.17±0.32 diopters (D), respectively, and for the IntraLase group were 20/12.5, 20/12.5, and 0.11±0.34 D, respectively. No statistically significant differenes were noted in UDVA, CDVA, or MRSE between groups (P>.05 for all).

CONCLUSIONS

Laser in situ keratomileusis with the Femto LDV created thin flaps regardless of level of opacity and induced no complications as compared to the IntraLase FS 60, where gas breakthrough was significantly more common.

Intraoperative flap complications in laser in situ keratomileusis with two types of microkeratomes

PURPOSE

To determine the incidence and types of intraoperative flap complications in laser in situ keratomileusis (LASIK) encountered with the Hansatome microkeratome and the Moria microkeratome.

METHODS

In this retrospective case series, all patients with intraoperative flap complications who were treated between June 1999 and July 2008 at the Eye Consultants Center in Riyadh, Saudi Arabia, were identified and reviewed.

RESULTS

Of the 4352 subjects who underwent bilateral primary LASIK procedure, intraoperative microkeratome complications were detected in 89 eyes of 83 patients. The overall incidence of flap complications was 89/8704 (1.00%): incomplete flaps occurred in 53 eyes (0.60%), followed by buttonhole flaps in 17 eyes (0.19%), free complete flaps in 10 eyes (0.11%), free partial flaps in 6 eyes (0.07%), sluffed epithelium in 2 eyes (0.023%), and a splitted flap (vertical flap cut) in 1 eye (0.01%). The incidence rates of intraoperative flap complications with the Hansatome microkeratome and the Moria microkeratome were 1.21% (41/3378) and 0.90% (48/5326), respectively (P = 0.19). There was a statistically significant difference between the two microkeratomes with regard to the incidence of buttonhole flaps: 0.33% (11/3378) for the Hansatome microkeratome versus 0.11% (6/5326) for the Moria microkeratome (P = 0.04).

CONCLUSION

Generally, the incidence rates of intraoperative flap complications with the Hansatome microkeratome and the Moria microkeratome were similar. However, buttonhole flaps occurred more often with the Hansatome microkeratome (a type of microkeratome that produces larger flaps). The commonest complication encountered was the incomplete flap, followed by the buttonhole flap and free flap.

Femtosecond laser vs mechanical microkeratome for hyperopic laser in situ keratomileusis

PURPOSE

To compare the outcomes of laser in situ keratomileusis (LASIK) performed with a femtosecond laser vs a mechanical microkeratome for the correction of low to moderate hyperopia.

DESIGN

Retrospective, nonrandomized, interventional, comparative case series.

METHODS

settings: Vissum Santa Hortensia, Madrid, Spain.study population and procedures: Patients who had undergone LASIK to correct their hyperopia using the 60-kHz IntraLase femtosecond laser were compared to age- and refraction-matched patients in whom the Moria M2 microkeratome was used. Visual and refractive results 3 months postoperatively were compared between both groups.

RESULTS

A total of 144 eyes were analyzed (72 in each group). Mean preoperative sphere was +3.45 ± 1.0 diopters (D) in the IntraLase group vs +3.18 ± 1.3 D in the M2 group (P = .1). Results 3 months postoperatively were: mean residual sphere, +0.44 ± 0.6D vs +0.72 ± 0.8 D (P = .02), respectively; uncorrected visual acuity (UCVA), 0.89 ± 0.2 vs 0.80 ± 0.2 (P = .04); best spectacle-corrected visual acuity (BSCVA), 0.96 ± 0.2 vs 0.92 ± 0.2 (P = .2); safety index, 0.97 ± 0.1 vs 0.98 ± 0.1 (P = .5); efficacy index, 0.89 ± 0.2 vs 0.84 ± 0.2 (P = .3).

CONCLUSIONS

Hyperopic LASIK performed with the IntraLase femtosecond laser seems to achieve better refractive results 3 months after the surgery compared to the M2 microkeratome, without significant differences in safety between both procedures.

[Comparison of Lasik with femtosecond laser versus Lasik with mechanical microkeratome: predictability of flap depth, corneal biomechanical effects and optical aberrations]

OBJECTIVES

To compare the predictability of flap thickness, high-order optic aberrations (HOAs), and biomechanical properties of cornea between patients treated by Lasik with mechanical microkeratome versus patients treated by FemtoLasik.

SETTING

Department of ophthalmology, Pellegrin University Hospital, Bordeaux, France.

PATIENTS AND METHODS

We conducted a retrospective study on 53 myopic patients who underwent Lasik with either mechanical microkeratome (MK group) or femtosecond laser (FS group). Refraction, central corneal thickness, high-order optic aberrations (HOAs), corneal hysteresis (CH), and corneal resistance factor (CRF), were analysed pre- and postoperatively in both groups. The central corneal thickness was measured with OCT-Visante(®) (Carl-Zeiss, Meditec), biomechanical parameters with ORA(®) (Reichert), and optical aberrations with the Wave Scan(®) (AMO) aberrometer.

RESULTS

We included 44 eyes of 22 patients in the MK group and 62 eyes of 31 patients in the FS group. Preoperatively, the mean best-corrected visual acuity was 0.95 in both groups. In the MK group, the flap was significantly thicker than expected (162/130 μm), but in the FS group, there was no significant difference (117/120 μm). The biomechanical properties of the cornea were lower in both groups independently of the flap cutting technique. The HOAs increased after Lasik and were not influenced by the flap cutting technique.

CONCLUSION

Neither mechanical microkeratome, nor femtosecond laser for flap creation, increases HOAs and the biomechanical changes of the cornea, according to ORA(®), significantly after Lasik.

Long-term comparison of corneal aberration changes after laser in situ keratomileusis: mechanical microkeratome versus femtosecond laser flap creation

PURPOSE

To compute and compare visual acuity, refractive outcomes, and anterior corneal aberration changes after myopic laser in situ keratomileusis (LASIK) with flap creation by a mechanical microkeratome and by a femtosecond laser.

SETTING

Private practice refractive surgery center, Valencia, Spain.

DESIGN

Comparative case series.

METHODS

Patients were assigned to have LASIK flap creation with a mechanical microkeratome (Carriazo-Barraquer) or a femtosecond laser (IntraLase). The Visx S2 excimer laser was used for myopic ablation in all cases. Main outcome measures included uncorrected and corrected distance visual acuities and the defocus equivalent. Higher-order aberrations (HOAs) were computed from the anterior corneal surface measured with topography for 4.0 mm and 6.0 mm pupil diameters before and 48 months after surgery.

RESULTS

The study evaluated 50 patients (98 eyes). The root mean square of HOAs increased postoperatively by a factor of approximately 1.9 in both groups and with both pupil diameters. There were no statistically significant differences between the 2 groups in the increase in anterior corneal aberrations, mean postoperative visual acuity, or residual refraction. All visual and optical performance metrics remained stable throughout the 4-year follow-up. There were no complications with flap creation and no postoperative complications.

CONCLUSIONS

The increase in anterior corneal aberrations after myopic LASIK was similar after mechanical microkeratome and femtosecond laser flap creation. Visual acuity, refraction, and the optical quality of the cornea after LASIK remained stable through 4 years postoperatively in both groups.

Subbasal nerve density and corneal sensitivity after laser in situ keratomileusis: femtosecond laser vs mechanical microkeratome

OBJECTIVE

To compare changes in subbasal nerve density and corneal sensitivity after laser in situ keratomileusis (LASIK) with the flap created by a femtosecond laser (bladeless) vs a mechanical microkeratome.

DESIGN

In a randomized paired-eye study, 21 patients received myopic LASIK with the flap created by a femtosecond laser in one eye and by a mechanical microkeratome in the fellow eye. Eyes were examined before and at 1, 3, 6, 12, and 36 months after LASIK. Central subbasal nerve density was measured by using confocal microscopy. Corneal mechanical sensitivity was measured by using a gas esthesiometer and was expressed as the ratio of mechanical threshold in eyes that received LASIK to mechanical threshold in concurrent control eyes.

RESULTS

Subbasal nerve density and corneal sensitivity did not differ between methods of flap creation at any examination. Mean (SD) nerve density was decreased at 1 month (bladeless, 974 [2453] μm/mm(2); microkeratome, 1308 [2881] μm/mm(2)) compared with the preoperative examination (bladeless, 10,883 [5083] μm/mm(2), P < .001; microkeratome, 12,464 [6683] μm/mm(2), P < .001) and remained decreased through 12 months (P < .001). Mechanical threshold ratios did not differ from that at the preoperative examination through 36 months for either LASIK treatment; when all LASIK eyes were combined, the mechanical threshold ratio was transiently higher (decreased sensitivity) at 1 month (1.29 [0.85]) compared with the preoperative examination (0.89 [0.73], P = .05).

CONCLUSIONS

The planar configuration of the femtosecond laser flaps is not associated with faster reinnervation compared with the microkeratome flaps. The prolonged decrease in subbasal nerve density after LASIK is not accompanied by a prolonged decrease in corneal sensitivity.

TRIAL REGISTRATION

clinicaltrials.gov Identifier NCT00350246.

Corneal shaping and ablation of transparent media by femtosecond pulses in deep ultraviolet range

PURPOSE

To assess the performance of a newly developed solid-state femtosecond ultraviolet (UV) laser system in corneal ablation.

SETTING

Vilnius University, Laser Research Centre, Vilnius, Lithuania.

METHODS

Femtosecond pulses in the deep UV range (205 nm) were obtained by the generation of the fifth-harmonic of an amplified Yb:KGW laser system (fundamental output at 1027 nm). Coupled with galvanometric beam-scanning mirrors, this system allowed ablation shaping of transparent media, including poly(methyl methacrylate) (PMMA), collagen, and ex vivo porcine corneas. The surfaces of ablated structures were characterized using a noncontact confocal optical profiler.

RESULTS

Spherical structures were successfully formed in all 3 materials tested. A 10.0 diopter refraction change in the cornea was produced in 180 seconds. The resulting surface quality was significantly higher (roughness length >100 microm versus approximately 6 microm) in gelatin and ex vivo corneas than in PMMA.

CONCLUSION

The solid-state femtosecond UV laser system seems an attractive alternative to the currently used ophthalmic argon-fluoride excimer laser system because of its small footprint, silent operation, and ability to generate femtosecond light pulses at both 1027 nm (suitable for flap creation) and 205 nm (corneal ablation).