Real-Time Wavefront Sensing at High Resolution with an Electrically Tunable Lens

We have designed, assembled, and evaluated a compact instrument capable of capturing the wavefront phase in real time, across various scenarios. Our approach simplifies the optical setup and configuration, which reduces the conventional capture and computation time when compared to other methods that use two defocused images. We evaluated the feasibility of using an electrically tunable lens in our camera by addressing its issues and optimizing its performance. Additionally, we conducted a comparison study between our approach and a Shack-Hartmann sensor. The camera was tested on multiple targets, such as deformable mirrors, lenses with aberrations, and a liquid lens in movement. Working at the highest resolution of the CMOS sensor with a small effective pixel size enables us to achieve the maximum level of detail in lateral resolution, leading to increased sensitivity to high-spatial-frequency signals.

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.

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.

Effect of flap homogeneity on higher-order aberrations induction after femtosecond LASIK for myopia

PURPOSE

To assess the relevance of the homogeneity of femtosecond laser flap thickness regarding induction of higher-order aberrations (HOAs).

SETTING

Clínica Rementería & Clínica Novovisión, Madrid, Spain.

DESIGN

Prospective observational study.

METHODS

Two hundred thirty-one patients underwent in situ keratomileusis using 5 different femtosecond lasers. The flap thicknesses were measured using anterior segment optical coherence tomography 3 months postoperatively. The same masked observer measured 6 symmetrical points nasally and temporally 1.0 mm, 2.0 mm, and 3.0 mm from the center of the flap in each case. HOAs induced in the cornea were measured using tomography.

RESULTS

Positive and significant correlations were found between HOA induction and the flap thickness heterogeneity 3.0 mm from the center of the flap. Pearson correlation coefficients for the induction of HOAs were third-order 0.17112 (P = .0224), fourth-order 0.22474 (P = .0026), fifth-order 0.16449 (P = .0282), coma-like 0.17370 (P = .0204), and total HOAs 0.18182 (P = .0151).

CONCLUSIONS

The amount of flap-thickness heterogeneity at 3.0 mm from the center of the flap created using femtosecond lasers was correlated with the magnitude of the HOAs induced.

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.

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.

Influences of Flap Shape and Hinge Angle on Opaque Bubble Layer Formation in Femtosecond Laser-Assisted LASIK Surgery

PURPOSE

To evaluate the effects of different flap shapes and hinge angles on opaque bubble layer (OBL) formation using a femtosecond laser for flap creation in LASIK surgery.

METHODS

This retrospective study evaluated 138 eyes of 73 patients who underwent femtosecond laser-assisted LASIK with a 150-kHz IntraLase femtosecond laser (Abbott Medical Optics, Inc., Santa Ana, CA) for myopic astigmatism and compared differences between different flap shapes and hinge angles on OBL formation. The surgical procedures were videotaped, and the patterns and sizes of the OBLs seen during surgery were analyzed. Preoperative and postoperative data including patient demographics, refractive status, keratometry, central corneal thickness, and intraoperative data (flap size and pocket parameters) were recorded. The eyes were divided into four groups based on the corneal flap shape (elliptical versus round) and hinge angle (50° versus 60°).

RESULTS

The preoperative demographic data, mean spherical errors, cylindrical power, and central corneal thickness were not significantly different among the groups. Of the 138 eyes, 107 (77%) developed an OBL covering a mean area of 13.8% ± 12.6% in each case. This area was significantly smaller in the elliptical flap with 60° hinge angle group (P < .05).

CONCLUSIONS

An oval-shaped flap with a larger hinge angle tended to result in less OBL formation in femtosecond laser-assisted LASIK. [J Refract Surg. 2017;33(3):178-182.].

SMILE and Wavefront-Guided LASIK Out-Compete Other Refractive Surgeries in Ameliorating the Induction of High-Order Aberrations in Anterior Corneal Surface

Purpose. To compare the change of anterior corneal higher-order aberrations (HOAs) after laser in situ keratomileusis (LASIK), wavefront-guided LASIK with iris registration (WF-LASIK), femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), and small incision lenticule extraction (SMILE). Methods. In a prospective study, 82 eyes underwent LASIK, 119 eyes underwent WF-LASIK, 88 eyes underwent FS-LASIK, and 170 eyes underwent SMILE surgery. HOAs were measured with Pentacam device preoperatively and 6 months after surgery. The aberrations were described as Zernike polynomials, and analysis focused on total HOAs, spherical aberration (SA), horizontal coma, and vertical coma over 6 mm diameter central corneal zone. Results. Six months postoperatively, all procedures result in increase of anterior corneal total HOAs and SA. There were no significant differences in the induced HOAs between LASIK and FS-LASIK, while SMILE induced fewer total HOAs and SA compared with LASIK and FS-LASIK. Similarly, WF-LASIK also induced less total HOAs than LASIK and FS-LASIK, but only fewer SA than FS-LASIK (P < 0.05). No significant difference could be detected in the induced total HOAs and SA between SMILE and WF-LASIK, whereas SMILE induced more horizontal coma and vertical coma compared with WF-LASIK (P < 0.05). Conclusion. FS-LASIK and LASIK induced comparable anterior corneal HOAs. Compared to LASIK and FS-LASIK, both SMILE and WF-LASIK showed advantages in inducing less total HOAs. In addition, SMILE also possesses better ability to reduce the induction of SA in comparison with LASIK and FS-LASIK. However, SMILE induced more horizontal coma and vertical coma compared with WF-LASIK, indicating that the centration of SMILE procedure is probably less precise than WF-LASIK.

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.

Postoperative ocular higher-order aberrations and contrast sensitivity: femtosecond lenticule extraction versus pseudo small-incision lenticule extraction

PURPOSE

To evaluate and compare changes in contrast sensitivity and ocular higher-order aberrations (HOAs) after femtosecond lenticule extraction (FLEx) and pseudo small-incision lenticule extraction (SMILE).

SETTING

Singapore National Eye Centre, Singapore.

DESIGN

Retrospective case series.

METHOD

Patients had femtosecond lenticule extraction (Group 1) or pseudo small-incision lenticule extraction (Group 2) between March 2010 and December 2011. The main outcome measures were manifest refraction, HOAs, and contrast sensitivity 1, 3, 6, and 12 months postoperatively.

RESULTS

Fifty-two consecutive patients (102 eyes) were recruited, 21 patients (42 eyes) in Group 1 and the 31 patients (60 eyes) in Group 2. The uncorrected and corrected distance visual acuities were significantly better in Group 2 than in Group 1 at 12 months (P = .032). There was no significant increase in 3rd- or 4th-order aberrations at 1 year and no significant difference between the 2 groups preoperatively or postoperatively. At 1 year, there was a significant increase in mesopic contrast sensitivity in Group 2 at 1.5 cycles per degree (cpd) (P = .008) that was not found in Group 1, and photopic contrast sensitivity at 6.0 cpd was higher in Group 2 (P = .027).

CONCLUSIONS

These results indicate that refractive lenticule extraction is safe and effective with no significant induction of HOAs or deterioration in contrast sensitivity at 1 year. Induction of HOAs was not significantly different between both variants of refractive lenticule extraction. However, there was significant improvement in photopic contrast sensitivity after pseudo small-incision lenticule extraction, which persisted through 1 year.

FINANCIAL DISCLOSURE

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

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.

LASIK-induced aberrations: comparing corneal and whole-eye measurements

PURPOSE

To compare the change in aberrations produced by laser-assisted in situ keratomileusis (LASIK) measured by either front surface corneal aberrometry or Hartmann-Shack whole-eye aberrometry.

METHODS

This was a retrospective case series from consecutive patients treated with LASIK at the London Vision Clinic, London, UK. Corneal and ocular wavefront data were collected before and after LASIK for myopia and hyperopia. To control for centration of corneal and whole-eye aberration measurements, only patients with pupil offset (measured as the distance between the corneal vertex and the entrance pupil center) of 0.25 mm or less were recruited. Corneal front surface wavefront was obtained from a Placido-based corneal topography system (Atlas), and whole-eye wavefront was measured by Hartmann-Shack aberrometry (WASCA) before and at least 3 months after surgery. All aberrations were calculated up to the fourth order for the 6-mm pupil diameter. Change in HORMS (higher-order root mean square [RMS]) and all individual Zernike coefficients from the second to the fourth order were compared.

RESULTS

One hundred myopic eyes and 50 hyperopic eyes were included for analysis. For myopic LASIK, the change measured by corneal aberrometry or whole-eye aberrometry differed on average by 0.077 μm for HORMS, by 0.024 μm for secondary astigmatism, and by 0.065 μm for spherical aberration (p ≤ 0.003). For hyperopic LASIK, there was no statistically significant difference between the change measured by corneal aberrometry and whole-eye aberrometry for third- and fourth-order individual Zernike coefficients (p ≥ 0.034). However, the change in HORMS measured by whole-eye aberrometry was 0.095 μm greater than that measured by corneal aberrometry (p < 0.001).

CONCLUSIONS

This study demonstrated that when measuring the change in higher-order aberrations induced by LASIK, corneal front surface aberrometry measurement was not interchangeable with whole-eye ocular aberrometry.

Randomized, contralateral eye study to evaluate the effect of standard and inverted side-cut angle on corneal biomechanical properties during femtosecond laser-assisted in situ keratomileusis

PURPOSE

To evaluate the effect of side-cut angle profile on corneal biomechanical properties after femtosecond laser in situ keratomileusis (FS-LASIK).

METHODS

Ninety-six myopic eyes of 48 patients underwent FS-LASIK. One eye of each patient was randomized to flap creation with a side-cut angle of 115°. The fellow eye flap side-cut angle was adjusted to 70°. Mean absolute error of flap diameter and mean change in Goldmann-correlated intra-ocular pressure (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), corneal resistance factor (CRF), p1 area, p2 area, p1 area 1 and p2 area 1 were compared between both groups.

RESULTS

Overall, the mean IOPg and CRF showed significant reduction at the end of 1 and 3 months, as well as between 1 and 3 months postoperatively (p ≤ 0.03). The mean IOPcc and CH showed significant reduction (p < 0.001) at the end of 3 months postoperatively. The parameters p1 area, p2 area, p1 area 1 and p2 area 1 changed significantly at the end of 1 and 3 months postoperatively (p < 0.001). There was no significant difference between both groups with regards to the mean change of IOPg, IOPcc, CH, CRF, p1 area, and p1 area 1. In 115° group, the mean absolute error in flap diameter was greater compared with 70° group (p = 0.014).

CONCLUSIONS

The stability of IOP and corneal biomechanical properties were not enhanced in FS-LASIK flaps with an inverted side-cut angle. The size of corneal flap created with 70° side-cut angle was more accurate compared with 115° side-cut angle.

Microkeratome versus femtosecond flaps: accuracy and complications

PURPOSE OF REVIEW

To update the knowledge on differences between mechanical microkeratome and femtosecond flaps for laser in-situ keratomileusis (LASIK) in terms of accuracy and complications.

RECENT FINDINGS

Corneal flaps created with the femtosecond laser present a more planar architecture and provide greater precision in flap diameter and thickness; a more uniform flap thickness across the flap diameter and it allows the surgeon to programme the angulation of the flap periphery. Femtosecond LASIK flaps are classically related to complications derived from a more intense inflammatory response, such as diffuse lamellar keratitis and transient light-sensitivity syndrome. Newer femtosecond models allow for much lower energy delivery to cut the flap, to the point the overall inflammatory response is not significantly different from the microkeratome. The incidence of complications such as epithelial defect and flap dislocations is higher with microkeratome flaps.

SUMMARY

This review examines the accuracy and complications of flaps created with femtosecond and microkeratome. Both femtosecond and microkeratome are able to create accurate LASIK flaps. Femtosecond LASIK flaps represent significant improvement in morphology and predictability with implications for safety.

Changes in custom biomechanical variables after femtosecond laser in situ keratomileusis and photorefractive keratectomy for myopia

PURPOSE

To analyze changes in new biomechanical descriptors with myopic femtosecond laser-assisted laser in situ keratomileusis (LASIK), compare them with the biomechanical response after photorefractive keratectomy (PRK) with similar levels of myopic ablation, and evaluate correlations between changes in custom variables and biomechanically relevant variables.

SETTING

Cleveland Clinic, Cleveland, Ohio, USA.

DESIGN

Cohort study.

METHODS

Custom biomechanical variables from the Optical Response Analyzer were assessed preoperatively and 1 and 3 months postoperatively. Differences between preoperative values and postoperative values were determined. Intraindividual change (preoperative value minus postoperative value) was calculated and compared with changes after PRK. The correlation of the change in each custom biomechanical variable with the preoperative central corneal thickness, residual stromal bed tissue ablated, and percentage of tissue depth altered was also studied.

RESULTS

The study enrolled 156 eyes of 156 consecutive patients. Fifteen variables changed significantly after femtosecond myopic LASIK and were stable postoperatively because no significant difference was shown between 1-month values and 3-month values. Comparison of the changes in biomechanical variables between LASIK and PRK eyes showed no significant differences. Surgical changes in several custom biomechanical variables correlated with the percentage of tissue depth altered.

CONCLUSIONS

The results provide the first reference values for a more comprehensive panel of indicators of the biomechanical response to myopic LASIK and PRK. Changes in custom variables reflected a consistent decrease in corneal biomechanical resistance to deformation after myopic femtosecond LASIK and PRK. For comparable attempted corrections, biomechanical changes were comparable between femtosecond laser-assisted LASIK and PRK.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosures are listed after the references.

Laser in situ keratomileusis in 2012: a review

Laser in situ keratomileusis (LASIK) is a safe and effective treatment for refractive error. A combination of technological advances and increasing surgeon experience has served to further refine refractive outcomes and reduce complication rates. In this article, we review LASIK as it stands in late 2012: the procedure, indications, technology, complications and refractive outcomes.

Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx(®) flex and comparison with a retrospective study of FS-laser in situ keratomileusis

PURPOSE

To present our initial clinical experience with ReLEx(®) flex (ReLEx) for moderate to high myopia. We compare efficacy, safety and corneal higher-order aberrations after ReLEx with femtosecond laser in situ keratomileusis (FS-LASIK).

METHODS

Prospective study of ReLEx compared with a retrospective study of FS-LASIK. ReLEx is a new keratorefractive procedure, where a stromal lenticule is cut by a femtosecond laser and manually extracted. Forty patients were treated with ReLEx on both eyes. A comparable group of 41 FS-LASIK patients were retrospectively identified. Visual acuity, spherical equivalent (SE) and corneal tomography were measured before and 3 months after surgery.

RESULTS

Preoperative SE averaged -7.50 ± 1.16 D (ReLEx) and -7.32 ± 1.09 D (FS-LASIK). For all eyes, mean corrected distance visual acuity remained unchanged in both groups. For eyes with emmetropia as target refraction, 41% of ReLEx and 61% of FS-LASIK eyes had an uncorrected distance visual acuity of logMAR ≤ 0.10 at day 1 after surgery, increasing to, respectively, 88% and 69% at 3 months. Mean SE was -0.06 ± 0.35 D 3 months after ReLEx and -0.53 ± 0.60 D after FS-LASIK. The proportion of eyes within ±1.00 D after 3 months was 100% (ReLEx) and 85% (FS-LASIK). For a 6.0-mm pupil, corneal spherical aberrations increased significantly less in ReLEx than FS-LASIK eyes.

CONCLUSIONS

ReLEx is an all-in-one femtosecond laser refractive procedure, and in this study, results were comparable to FS-LASIK. Refractive predictability and corneal aberrations at 3 months seemed better than or equal to FS-LASIK, whereas visual recovery after ReLEx was slower.

Comparison of optical quality parameters and ocular aberrations after wavefront-guided laser in-situ keratomileusis versus wavefront-guided laser epithelial keratomileusis for myopia

BACKGROUND

To compare optical quality, ocular scattering, and higher-order aberrations (HOAs) after laser in-situ keratomileusis (LASIK) versus laser epithelial keratomileusis (LASEK).

METHODS

A total of 47 eyes from 47 participants who had undergone LASIK (group I) or LASEK (group II) procedure at least 6 months prior were enrolled. Ocular aberrations and modulation transfer function (MTF) values measured using iTrace, a ray-tracing type aberrometer, were compared to MTF (modulation transfer function) cut-off values, Strehl ratio, and objective indices of scattering obtained using the Objective Quality Analysis System II (OQAS II).

RESULTS

There was no significant correlation between the postoperative optical quality parameters and the HOAs between both groups. In group I, the MTF cut-off value was significantly correlated with cylinder refraction (p = 0.037), and the objective scattering index (OSI) was positively correlated with spherical equivalent (p = 0.023). In group II, there was a statistically significant correlation between the OSI and achieved refractive correction (p = 0.001). Regression analysis showed that the OSI was the most significant predictor of MTF cut-off values after refractive surgery. Additionally, MTF values measured by OQAS were significantly lower than those measured by iTrace without correlation.

CONCLUSION

Optical quality after refractive surgery may be influenced by not only ocular aberrations but also by scattering. Even though the accuracies of the machines used in this study to measure optical quality have yet to be proven, this study showed limited correlation among the values measured using the two different machines after refractive surgery. Therefore, for more generalized evaluation of visual function after refractive surgery, more advanced optical devices still need to be developed.

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.

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.

Effect of different femtosecond laser-firing patterns on collagen disruption during refractive lenticule extraction

PURPOSE

To evaluate the changes in corneal collagen architecture subjected to different laser-firing patterns during refractive lenticule extraction.

SETTING

Singapore Eye Research Institute, Singapore.

DESIGN

Experimental study.

METHODS

Refractive lenticule extraction was performed in rabbits without lenticule removal. Rabbits were divided into 4 groups that had incisions in the following firing patterns: (A) from periphery in (lenticule's posterior surface) and from center out (lenticule's anterior surface); (B) from center out and from center out; (C) from periphery in and from periphery in; and (D) from center out and from periphery in. The corneas were collected 18 hours postoperatively and were subjected to immunofluorescent staining of fibronectin, CD11b, and collagen type I. Ultrastructural analysis was performed using transmission electron microscopy (TEM).

RESULTS

Refractive lenticule extraction-treated corneas showed no significant difference in fibronectin and CD11b expression. Similar expression patterns of collagen type I were observed in corneas that had femtosecond firing patterns A, B, and C; however, a discontinuous and relatively more intense staining pattern along the anterior plane of the lenticule was detected in corneas treated with pattern D. The TEM also showed a more disrupted collagen arrangement along the anterior incision site in pattern D-treated corneas.

CONCLUSIONS

Differential laser firing patterns during refractive lenticule extraction resulted in different levels of collagen derangement along the anterior plane of the lenticule, with pattern D showing the most disrupted surface. Such disruption in the collagen architecture might affect postoperative visual recovery and refractive outcomes.

FINANCIAL DISCLOSURE

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

Wavefront-optimized excimer laser in situ keratomileusis for myopia and myopic astigmatism: refractive outcomes and corneal densitometry

PURPOSE

To determine the refractive outcomes of wavefront-optimized laser in situ keratomileusis (LASIK) treatments, in particular to measure corneal densitometry after LASIK using the densitometry function of the Pentacam Scheimpflug system.

SETTING

Division of Ophthalmology and Visual Sciences, University of Nottingham, United Kingdom.

DESIGN

Cohort study.

METHODS

Changes in postoperative visual acuity, refraction, and contrast sensitivity were evaluated after wavefront-optimized laser treatment. Corneal densitometry was evaluated with the Scheimpflug system before and after LASIK.

RESULTS

One year postoperatively, the uncorrected distance visual acuity was 6/6 or better in 92% of eyes and 6/9 or better in all eyes. Eighty-six percent of eyes had no change in the corrected distance visual acuity (CDVA); 4% gained 1 or more lines. Wavefront-optimized LASIK was stable over 1 year postoperatively. Eighty-nine percent of eyes were within ±0.50 diopter (D) and 100% were within ±1.00 D of the intended correction 1 year postoperatively. Contrast sensitivity showed a nonsignificant improvement (1.55 ± 0.10 [SD] preoperatively to 1.57 ± 0.09 12 months postoperatively) (P > .05). There was a nonsignificant increase in corneal densitometry 1 year postoperatively (from 12.72 ± 2.43 to 13.04 ± 2.58) (P > .05). No correlation was found between corneal densitometry and contrast sensitivity or CDVA.

CONCLUSIONS

Wavefront-optimized LASIK gave excellent refractive and visual outcomes and did not seem to affect corneal densitometry significantly 1 year postoperatively. However, larger studies may show a masked effect on corneal densitometry.

FINANCIAL DISCLOSURE

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

Comparison of the Ratio of Keratometric Change to Refractive Change Induced by Myopic Ablation

PURPOSE:

To compare the ratio of keratometric change (ΔK) to refractive change (ΔSE) induced by refractive laser ablation.

METHODS:

The charts of 3337 eyes that underwent LASIK or photorefractive keratectomy (PRK) from 2002 to 2011 were retrospectively reviewed, and the ratio ΔK/ΔSE measured at 3 months postoperatively was compared between eyes with low ΔSE (0.00 to 2.99 diopters [D]), moderate ΔSE (3.00 to 5.99 D), and high ΔSE (6.00 to 8.99 D). Eyes were further stratified by LASIK vs PRK; custom vs conventional treatments; microkeratome vs IntraLase (Abbott Medical Optics Inc) femtosecond laser–created flaps; and flat (38.00 to 41.99 D) vs moderate (42.00 to 45.99 D) vs steep (46.00 to 49.99 D) preoperative keratometry, and the ratio ΔK/ΔSE was similarly compared.

RESULTS:

Significant differences were found in the ratio ΔK/ΔSE among eyes with low ΔSE (1.00±0.50 D), moderate ΔSE (0.83±0.19 D), and steep ΔSE (0.80±0.15 D) ( P <.001), and between eyes with moderate and high ΔSE in LASIK vs PRK, custom vs conventional treatments, and microkeratome vs IntraLase flaps. Significant differences in the ratio ΔK/ΔSE were also found in eyes with low, moderate, and high ΔSE regardless of preoperative keratometry. The ratio ΔK/ΔSE compared with ΔSE follows a nonlinear pattern and tended to be higher and more variable at lower amounts of correction.

CONCLUSIONS:

The change in simulated keratometry required to achieve 1.00 D of myopic refractive correction decreased as the amount of refractive change increased, was more variable with lower amounts of correction, and followed a nonlinear relationship. Many variables, such as LASIK vs PRK, custom vs conventional, and microkeratome vs IntraLase flaps, affected the ratio of ΔK/ΔSE for moderate and high myopic corrections.

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.

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.

Comparison of intraoperative subtraction pachymetry and postoperative anterior segment optical coherence tomography of laser in situ keratomileusis flaps

PURPOSE

To prospectively compare intraoperative subtraction pachymetry flap thickness measurements and postoperative anterior segment optical coherence tomography (AS-OCT) flap thickness measurements in eyes that had laser in situ keratomileusis (LASIK) flap creation with a femtosecond laser or a mechanical microkeratome.

SETTING

Stanford Eye Laser Center, Stanford University School of Medicine, Stanford, California, USA.

DESIGN

Comparative case series.

METHODS

Each patient received wavefront-guided LASIK using an Intralase femtosecond laser in 1 eye and a Hansatome mechanical microkeratome in the fellow eye. Flap morphology was assessed with an ultrasound pachymeter intraoperatively and an AS-OCT system postoperatively at 1 year.

RESULTS

Thirty-six eyes (18 patients) were enrolled. Intraoperative subtraction pachymetry consistently underestimated mechanical microkeratome flap thickness compared with postoperative AS-OCT (P<.001). There was no significant difference between intraoperative subtraction pachymetry and postoperative AS-OCT measurements for femtosecond flaps (P=.38). The overall mean variation in flap thickness (ie, mean deviation from targeted flap thickness) was 2.6 μm (range 3 to 11 μm) with the femtosecond laser and 14.2 μm (range 17 to 52 μm) with the mechanical microkeratome (P<.001). Postoperative AS-OCT measurements showed femtosecond flaps had a planar configuration and mechanical microkeratome flaps had a meniscus-shaped configuration.

CONCLUSIONS

The femtosecond laser created more uniformly planar flaps than the mechanical microkeratome as measured by intraoperative subtraction pachymetry and postoperative AS-OCT. Postoperative AS-OCT measurements varied less than intraoperative subtraction pachymetry measurements for mechanical microkeratome flaps.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.

Comparison of the predictability, uniformity and stability of a laser in situ keratomileusis corneal flap created with a VisuMax femtosecond laser or a Moria microkeratome

This prospective study compared the predictability, uniformity and stability of laser in situ keratomileusis corneal flap thickness created by a femtosecond laser or a classic microkeratome. Twenty-five femtosecond laser (VisuMax, Carl Zeiss Meditec) flaps and 38 microkeratome (Moria M3) flaps were measured using anterior segment optical coherence tomography at 1 week, 1 month and 6 months postoperatively. Flap thickness at seven points on each of the four meridians was calculated. At 6 months, VisuMax flaps showed better prediction than Moria flaps for central flap thickness. The standard deviation within individual flaps was smaller for VisuMax flaps and their index of symmetry was better. The mean thicknesses among the four eccentricities in the VisuMax flaps were the same, while Moria flaps were thicker at the 3-mm radius compared with the centre. The VisuMax femtosecond laser created corneal flaps with better predictability and uniformity, and similar reproducibility and stability, compared with the microkeratome.

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.

Effects of advanced surface ablations and intralase femtosecond LASIK on higher order aberrations and visual acuity outcome

BACKGROUND/AIMS

To study the changes in wavefront (ocular) and corneal higher order aberrations (HOAs) and visual acuity (VA) outcome following wavefront-guided advanced surface ablation (ASA) techniques and intralase femtosecond LASIK (iLASIK) in myopia treatment.

METHODS

Ocular aberration and corneal topography of 240 eyes in the ASA techniques (this was equally divided into a flap-on group where the epithelial flap was preserved and reapplied to the photoablated stromal bed and a flap-off group when the epithelial flap was discarded during the procedure), and 138 eyes in the iLASIK group were obtained before and 3 months following treatment. The correlation of aberrations with best spectacle-corrected visual acuity was analyzed.

RESULTS

At 3 months, there was statistically significant (P < 0.001) surgically induced increase in spherical aberration (SA) in each of the techniques for both ocular and corneal analysis. iLASIK induced significantly less ocular and corneal HOAs (P < 0.001). The mean manifest refractive spherical equivalent was closer to attempted correction compared to other groups (P < 0.001). Eighty-three eyes (70%) of flap-on, 80 (67%) flap-off and 94 eyes (68%) in the iLASIK group achieved 20/20 uncorrected VA. Fifteen eyes (11%) accomplished 20/12.5 or better in iLASIK compared to 4 (3%) for flap-on and 7 (6%) for flap-off ASA group. Only the flap-off treatment showed a consistent correlation between the corrected aberrations and visual performance.

CONCLUSION

At 3 months, all procedures resulted in a significant increase in HOAs and SA. All had comparable 20/20 VA and 11% of iLASIK patients achieved 20/12.5 or better level.

Alternative applications of the femtosecond laser in ophthalmology

PURPOSE

To provide an update of novel applications for the femtosecond (FS) laser in ophthalmology.

DESIGN

Perspective, literature review, case report, and commentary.

METHODS

Literature review.

RESULTS

The many advantages of etching flaps with the FS laser for laser in situ keratomileusis (LASIK) have been well established. Alternative applications of the FS have been approved and are now used in clinical practice. In refractive ophthalmology, the FS laser can be used for lenticule extraction to correct myopia and intrastromal biochemical manipulation to correct presbyopia. This laser can be used for preparing host and donor tissue for both full thickness and lamellar keratoplasty. Research is underway, exploring ways to employ the FS laser for different stages of cataract surgery. Cosmetic procedures with FS-assisted tattooing serve to correct leukoria.

CONCLUSIONS

Advancements in technology have allowed measurable improvements in the surgical safety, efficiency, speed, and versatility of FS lasers in ophthalmology.

A morphological study of corneal flap after thin-flap laser-assisted in situ keratomileusis by anterior segment optical coherence tomography

This prospective study assessed corneal flap morphology in 115 patients undergoing laser-assisted in situ keratomileusis (LASIK). Flaps were created using the Moria M2 90-μm or KM-5000D 110-μm microkeratomes. Flap thickness was measured using anterior segment optical coherence tomography at seven points in a 7-mm diameter zone 1 h, 1 day, 3 days, 1 week and 1 month after surgery. Flap accuracy, reproducibility, uniformity and changes over time were evaluated. The Moria M2 microkeratome created flaps with less accuracy in the centre than the KM-5000D microkeratome (114.06 ± 6.46 μm vs 128.39 ± 6.79 μm, respectively, at 1 week). For both microkeratomes, flap thickness varied between most of the peripheral areas and the central point. Both microkeratomes created flaps with good central predictability and reproducibility, but high variation and significant deviation from intended thickness were observed in peripheral flap thickness.

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.

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).

Femtosecond laser in laser in situ keratomileusis

Flap creation is a critical step in laser in situ keratomileusis (LASIK). Efforts to improve the safety and predictability of the lamellar incision have fostered the development of femtosecond lasers. Several advantages of the femtosecond laser over mechanical microkeratomes have been reported in LASIK surgery. In this article, we review common considerations in management and complications of this step in femtosecond laser-LASIK and concentrate primarily on the IntraLase laser because most published studies relate to this instrument.

Corneal aberrations and visual acuity after laser in situ keratomileusis: femtosecond laser versus mechanical microkeratome

PURPOSE

To compare corneal high-order aberrations and visual acuity after laser in situ keratomileusis (LASIK) with the flap created by a femtosecond laser (bladeless) to LASIK with the flap created by a mechanical microkeratome.

DESIGN

Prospective, randomized, paired-eye study.

METHODS

Fellow eyes of 21 patients with myopia or myopic astigmatism were randomized by ocular dominance. Corneal topography and visual acuity were measured before and at 1, 3, 6, 12, and 36 months after LASIK. Wavefront errors from the anterior corneal surface were calculated from the topography data over 4- and 6-mm-diameter pupils and decomposed into Zernike polynomials to the 6th order.

RESULTS

There were no differences in corneal total high-order aberrations, spherical aberration, coma, or trefoil between methods of flap creation at any examination over 4- and 6-mm-diameter pupils. Over a 6-mm pupil, total high-order aberrations increased by 1 month after LASIK with both treatments (P <or= .001) and remained increased through 36 months (P <or= .001). Uncorrected and best-corrected visual acuity did not differ between methods at any examination and remained stable postoperatively through 3 years; the minimum detectable difference in visual acuity between treatments was <or=0.1 logMAR (<or=1 line of vision, alpha = 0.05/6, beta = 0.20, n = 21).

CONCLUSIONS

The planar configuration of the femtosecond laser flap did not offer any advantage in corneal high-order aberrations or visual acuity through 3 years after LASIK. Corneal high-order aberrations remain stable through 3 years after LASIK.