Incidence, possible risk factors, and potential effects of an opaque bubble layer created by a femtosecond laser

Comparison of risk factors for OBL in FS-LASIK and SMILE correction for myopia and myopia astigmatism

BACKGROUND

To find out the incidence and risk factors of opaque bubble layer (OBL) in eyes with myopia and myopic astigmatism following femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE).

METHODS

A total of 1076 eyes from 569 patients who had FS-LASIK or SMILE were included in the retrospective research. For each kind of surgery, eyes were separated into two groups: "OBL" groups and "no OBL" groups. In the FS-LASIK group, eyes that developed OBL were split into "hard OBL" and "soft OBL" groups. The incidence and size of OBL were analyzed after watching the surgical procedure videotaped during the operation and taking screenshots. Surgical parameters, including sphere, cylinder, keratometry, corneal thickness, flap thickness, cap thickness, lenticule thickness, and visual acuity, were compared.

RESULTS

In the FS-LASIK surgery, the incidence of OBL was 63.2% (347 eyes). A thicker central corneal thickness (CCT) was the only independent risk factor affecting the OBL area (β = 0.126, P = 0.019). One hundred and thirty of these eyes had hard OBL, and the flap thickness of these eyes was thinner than that of those with soft OBL (P = 0.027). In the SMILE group, 26.6% (140 eyes) developed OBL. A higher flat keratometry (K) and a thicker residual stromal thickness (RST) were risk factors affecting the OBL area (β = 0.195, P = 0.024; β = 0.281, P = 0.001).

CONCLUSION

The incidence of OBL differs between the FS-LASIK surgery and the SMILE surgery. There are differences in the factors influencing OBL between the two surgeries.

Effect of corneal flap thickness on opaque bubble layer formation in Visumax FS-LASIK using GEE analysis

Introduction

This study aimed to investigate two types of corneal flap thickness on opaque bubble layer (OBL) formation in Visumax femtosecond laser-assisted stromal for situ keratomileusis (FS-LASIK).

Methods

This retrospective study analyzed 203 eyes of 103 patients (32 men and 71 women) who underwent Visumax FS-LASIK between January 2020 and June 2020, and according to corneal flap thickness, they were divided into the 100-μm group (64 eyes) and the 110-μm group (139 eyes). Anterior-segment examination revealed no abnormal findings. Preoperatively, intraocular pressure (IOP), central corneal thickness (CCT), residual stromal thickness (RST), spherical power, cylindrical power, flat keratometry (K1), steep keratometry (K2), and biomechanical parameters including deformation amplitude (DA) ratio, Integrated Radius, stiffness parameter at first applanation (SP-A1), and Ambrosio relational thickness to the horizontal profile (ARTh) were evaluated. Primary outcomes were the incidence of OBL formation in the two groups compared by the Chi-square test and the correlation between the incidence of OBL and the above preoperative data by Spearman's Rho test. Secondary outcomes were the comparisons corrected by the generalized estimating equation (GEE) model.

Results

The incidence of OBL formation in the 100-μm group was 59.4 %, which was higher than that in the 110-μm group (23.0 %) with a significant difference (χ2 = 25.635, P < 0.001). The thinner corneal flap thickness (r = -0.355, P < 0.001) and higher spherical power (r = -0.142, P < 0.05) correlated with OBL formation. Higher K1 (r = 0.217, P < 0.01) and K2 (r = 0.198, P < 0.01) also correlated with OBL formation. The results of the GEE correction analysis showed higher rates of OBL formation in the 100-μm group (odds ratio [OR] = 4.704, 95 % CI 1.681-13.161, P < 0.01).

Conclusions

OBL was more likely to occur with the 100-μm corneal flap than with the 110-μm corneal flap in Visumax FS-LASIK. The risk of OBL formation in the 100-μm group was 4.704 times higher than that in the 110-μm group.

VisuMax Flap 2.0: a flap plus technique to reduce incidence of an opaque bubble layer in femtosecond laser–assisted LASIK

Purpose

To evaluate the incidence of an opaque bubble layer (OBL) in femtosecond laser–assisted in situ keratomileusis (FS-LASIK) flaps created with VisuMax Flap 2.0 as a result of a modification in the parameters of the flap programming.

Methods

This retrospective study was comprised of 1400 eyes of 715 patients who received FS-LASIK surgery. OBLs were measured and reported as a percentage of the flap area to identify the incidence and extent. Flap creation, which is a modification technique, was performed with 8.1-mm flap diameters plus 0.3-mm enlarged interlamellar photodisruption (group Flap 2.0). The same flap diameters without extra photodisruption as the previous standard setting were also implemented (group Flap 1.0). The preoperative measurements, including sphere, cylinder, keratometry, and intraoperative characteristics such as flap size and thickness, were documented. Possible risk factors for the occurrence of OBLs were investigated in this study.

Results

The incidence of an OBL was reduced when using the Flap 2.0 program (31.4%) compared to the Flap 1.0 program (63.7%). The area of hard and soft OBLs created by the Flap 2.0 program is smaller than those created by the Flap 1.0 program (P = 0.007 and P < 0.001). Multivariate logistic regression indicated that a thinner flap (P = 0.038) and a higher sphere (P = 0.001) affected the chance of hard OBLs occurring.

Conclusion

The VisuMax Flap 2.0 program promotes gas venting by enlarging the interlamellar photodisruption size. The incidence and extent of OBLs appear to be reduced significantly when the Flap 2.0 program is applied.

Femtosecond laser deep lamellar keratoplasty

We aimed to develop a novel and effective technique for creating a smooth deep lamellar dissection of the cornea using a femtosecond (FS) laser for deep anterior lamellar keratoplasty (DALK), we conducted a retrospective eye bank study. Thirteen fresh human corneas were mounted on an artificial anterior chamber, and deep lamellar cuts were made with a 500-kHz VisuMax FS laser at a level of 50-80 μm anterior to the Descemet's membrane (DM). A posterior diameter of 8 mm with a side cut angle of 110° was used for the anterior penetrating side cut. The anterior lamellar tissue was bluntly dissected. The residual posterior stromal beds and side cuts were examined with microscopy and intraoperative optical coherence tomography (OCT) and post-cut endothelial cell evaluations. All corneas revealed a smooth residual posterior stromal bed without any visible irregularities or ridges by microscopy and OCT imaging. Six corneas were suitable for post-cut endothelial cell evaluation 2 days after laser cut, with no significant endothelial cell loss post-laser and blunt dissection of the posterior stroma. FS laser deep lamellar keratoplasty utilizing an ultrafast laser to produce a smooth deep stromal dissection followed by blunt dissection and removal of the anterior stromal tissue yields a consistent and smooth residual stromal bed. The creation of a smooth lamellar dissection in the deep posterior cornea may result in more consistent DALK without the need for air bubble or manual baring of DM that has the risk for DM perforation.

Flap-making patterns and corneal characteristics influence opaque bubble layer occurrence in femtosecond laser-assisted laser in situ keratomileusis

Background

Opaque bubble layer (OBL), which generates from photo-disruptive procedures on the cornea, has been a common phenomenon during femtosecond laser-assisted refractive surgeries and it would potentially impact eye tracking and flap lifting. And we have observed that an updated flap-making pattern could form less OBL clinically than the traditional pattern, which needed further approval. Thus, the purpose of this study is to prove our observation and investigate the possible risk factors related to the occurrence and type of OBL in laser in situ keratomileusis (LASIK) flaps using the Visumax laser system.

Methods

This prospective study included 167 eyes of 86 patients (mean age: 27.5 ± 6.1 years) undergoing bilateral femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia/myopic astigmatism by the same surgeon from April 2020 to August 2020. Preoperative data on refraction, central corneal thickness (CCT), and keratometry as well as intraoperative data were included for analysis. A new flap-making pattern creating an offset between flap-cut and side-cut was adopted to compare with the traditional pattern. The operation video of flap formation was analyzed to identify the existence and type of OBL. The area covered by OBL and the ratio of OBL to flap were calculated using Image J software.

Results

Among 167 eyes, 54 eyes (32.3%) developed OBLs, consisting of 31 as hard OBL coexisting with soft OBL, and 23 as soft OBL alone. The OBL incidence was significantly reduced in eyes with the new flap-making pattern compared with the traditional pattern (13.8% vs. 52.5%, P < 0.001). Hard OBLs had larger area ratios than soft OBLs (14.3 ± 8.3% vs. 1.1 ± 1.8%, P < 0.001). Univariate analyses revealed that eyes with more myopia, thicker CCT, and traditional flap-making patterns were more likely to develop OBLs. Multivariate analysis further confirmed that more myopia, thicker CCT, and traditional flap-making pattern were risk factors for OBLs. A Larger corneal diameter was associated with a higher incidence of hard OBL when applying the traditional flap-making process.

Conclusion

More myopia, thicker CCT, and larger corneal diameter were risk factors for OBL development during flap creation, whereas a flap-making pattern with an offset between flap-cut and side-cut could reduce the incidence of OBL.

Flap Thickness and the Risk of Complications in Mechanical Microkeratome and Femtosecond Laser In Situ Keratomileusis: A Literature Review and Statistical Analysis

INTRODUCTION

A recent Cochrane review found no difference in visual acuity outcomes between femtosecond-assisted laser in situ keratomileusis (LASIK) and LASIK using mechanical microkeratomes (MMKs). This study compares the flap thickness and risk of complications related to flap creation using femtosecond lasers and MMKs.

METHODS

PubMed and the Web of Science are used to search the medical literature. An extensive search is performed to identify the flap thickness and complications of LASIK as reported up to 15 July 2021. The following keywords are used in various combinations: Corneal flap, femtosecond laser, laser in situ keratomileusis, laser-assisted in situ keratomileusis, LASIK, mechanical microkeratome.

RESULTS

After removing duplicates and irrelevant studies, 122 articles were included for review. Pooled differences for intended vs. postoperative flap thickness using MMKs and femtosecond laser were -4.07 μm (95% CI: -19.55, 3.24 μm) in studies on the MMK and 5.43 μm (95% CI: 2.30, 7.84 μm; p < 0.001), respectively. After removing the studies evaluating outcomes of the old generation Hansatome MMKs (which had a significantly greater variation of flap thickness), the pooled difference for newer MMKs was 4.97 μm (95% CI: 0.35, 9.58 μm; p < 0.001), but the results still favored the femtosecond laser. Uncommon and mild complications unique for the femtosecond LASIK are epithelial gas breakthrough, opaque bubble layer, transient light sensitivity syndrome, and rainbow glare. A single study reported a very low, but stastically different risk of postoperative flap slippage (0.033% for MMK LASIK, and 0.003% for femtosecond LASIK, respectively).

CONCLUSION

In both manual microkeratome and femtosecond LASIK, intra- and postoperative complications were uncommon. The evidence of the superiority of one technique in terms of complications over another cannot be indisputably stated.

Complications of laser-assisted in situ keratomileusis

Laser-assisted in situ keratomileusis (LASIK) is one of the most commonly performed kerato-refractive surgery globally. Since its introduction in 1990, there has been a constant evolution in its technology to improve the visual outcome. The safety, efficacy, and predictability of LASIK are well known, but complications with this procedure, although rare, are not unknown. Literature review suggests that intraoperative complications include suction loss, free cap, flap tear, buttonhole flap, decentered ablation, central island, interface debris, femtosecond laser-related complications, and others. The postoperative complications include flap striae, flap dislocation, residual refractive error, diffuse lamellar keratitis, microbial keratitis, epithelial ingrowth, refractive regression, corneal ectasia, and others. This review aims to provide a comprehensive knowledge of risk factors, clinical features, and management protocol of all the reported complications of LASIK. This knowledge will help in prevention as well as early identification and timely intervention with the appropriate strategy for achieving optimal visual outcome even in the face of complications.

A microscopic study of the corneal stromal lenticules extracted during femtosecond laser-assisted small incision lenticule extraction

The aim of the present study was to investigate the histological and morphological characteristics of corneal stromal lenticules extracted during femtosecond laser-assisted small incision lenticule extraction (SMILE) surgery by light and electron microscopy. A total of 20 human corneal stromal lenticules extracted during SMILE surgery were sent for microscopic examination immediately after surgery. Of these, six were observed under a light microscope and 14 were observed under an electron microscope. The smoothness of the front and rear surface of the lenticules observed under an electron microscope was rated on a scale of 0 to 4 according to unified evaluation criteria and the scores were statistically compared. Under the light microscope, the edge of the cross section of the corneal stromal lenticules was deeply stained and certain burrs and broken collagen fibers were observed. The swollen corneal stromal fibers were distributed irregularly, with a few bubbles of different sizes. Under the electron microscope, the surface of the lenticules ablated using a femtosecond laser was not perfectly smooth and the front surface was smoother than the rear surface. The side edge of the lenticules ablated using a femtosecond laser was not as regular as the edge cut using microscissors. Necrosis and dissolution of collagen fibers were observed near the surface of the lenticules. In conclusion, the surface quality of corneal stromal lenticules ablated using a femtosecond laser was not optimal when observed under a microscope. Increased attention should be paid to the histology and morphology of the corneal surface following laser ablation.

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.

Incidence and Risk Factors of Opaque Bubble Layer Formation According to Flap Thickness During 500-kHz FS-LASIK

PURPOSE

To present the incidence, risk factors, and effect of opaque bubble layer (OBL) formation during flap creation in laser-assisted in situ keratomileusis (LASIK) with a 500-kHz femtosecond laser on visual performance.

METHODS

In this retrospective study, preoperative characteristics (age, sex, keratometric value, spherical equivalent, and central corneal thickness) and intraoperative surgical factors (used energy, docking type, and flap thickness) were compared between eyes with and without OBL formation during flap creation. Possible risk factors for specific types of OBLs were analyzed.

RESULTS

One hundred thirty-five eyes of 71 patients underwent LASIK, and OBL developed in 98 eyes (72.59%). In the univariate analysis, the greater than 80-µm flap group was associated with a lower OBL occurrence than the 80-µm flap group (P = .0424, odds ratio [OR] = 0.481) and hard docking was associated with increased OBL formation (P = .0001, OR = 6.859). In the multivariate analysis, hard docking was a risk factor for OBL development (P = .0003, OR = 6.329). In the subgroup analysis, hard docking had a marginal effect on OBL occurrence in the 80-µm flap group (P = .086, OR = 3.564), but it had a strong effect in the greater than 80-µm flap group (P = .0018, OR = 10.210).

CONCLUSIONS

Hard docking is a risk factor for OBL development. However, hard docking had a small effect on OBL occurrence in the 80-µm flap group during LASIK. OBL formation did not affect visual performance. [J Refract Surg. 2019;35(9):583-589.].

Incidence and management of intraoperative complications during small-incision lenticule extraction in 3004 cases

PURPOSE

To assess the intraoperative complications during small-incision lenticule extraction (SMILE) for myopia and myopic astigmatism correction and evaluate visual outcomes 6 months postoperatively.

SETTING

Tianjin Eye Hospital, Tianjin, China.

DESIGN

Retrospective case series.

METHODS

Patients who had small-incision lenticule extraction surgery were examined 1 day, 7 days, 1 month, 3 months, and 6 months postoperatively. Demographic characteristics, visual outcomes, and intraoperative complications were recorded. Moreover, the incidence and management of the complications and the potential factors were analyzed.

RESULTS

Of the 3004 eyes (1511 patients), 134 (4.46%) had intraoperative complications, including suction loss (28 cases [0.93%]), incisional bleeding (28 cases [0.93%]), opaque bubble layer (22 cases [0.73%]), subconjunctival hemorrhage (20 cases [0.67%]), black areas (10 cases [0.33%]), unintended posterior plane dissection (10 cases [0.33%]), tearing of the lenticule (8 cases [0.27%]), abrasion at the incision (5 cases [0.17%]), and inaccurate laser pulse placement due to eye movement (3 cases [0.10%]). The complications were resolved instantaneously using appropriate management procedures; all cases had good visual outcomes. Six months postoperatively, 99.80% of cases had an uncorrected distance visual acuity better than 20/25 and the mean corrected distance visual acuity was -0.06 logarithm of the minimum angle of resolution ± 0.07 (SD).

CONCLUSIONS

Although small-incision lenticule extraction shows promising outcomes for correction of myopia and myopic astigmatism, intraoperative complications still inevitably occur. However, satisfactory visual outcomes may be achieved using appropriate management techniques.

Paired eye-control study of unilateral opaque bubble layer in femtosecond laser assisted laser in situ keratomileusis

AIM

To investigate the predictive factors of the opaque bubble layer (OBL) compared to the fellow eye of same patients in FS200 femtosecond laser assisted laser in situ keratomileusis (FS-LASIK).

METHODS

This study consisted of 60 consecutive patients (120 eyes) with unilateral OBL during FS-LASIK. Eyes were divided into OBL (the OBL eyes) and OBL-free groups (the fellow eyes) based on the occurrence of OBL. The preoperative demographic data, refraction, keratometry, corneal astigmatism, pachymetry, intraocular pressure and intraoperative data including the outlet location of gas diffusing canal were collected. Conditional logistic regression analysis was performed to find the associated factors with OBL in the two groups by determining odds ratios (OR) and 95%CI.

RESULTS

The preoperative demographic data, mean spherical errors, mean K value, suction time, intraocular pressure and central cornea thickness were not significantly different between the two groups. The outlet location of gas diffusing canal (P<0.01, OR 7.16, 95%CI 2.53-20.32) and the corneal astigmatism (P=0.013, OR 0.13, 95%CI 0.03-0.65) were significantly associated with the incidence of OBL by multivariate logistic regression analysis. Visual acuity, efficacy, and safety were comparable between the two groups two months after surgery except for a slightly lower predictability value for the hard OBL eyes.

CONCLUSION

The reduction of the incidence of OBL is obvious when the outlet of gas diffusing canal located at the posterior border of the corneoscleral limbus. This is probably consequent to more effectiveness of gas diffusing canal. Corneal astigmatism is also an independent protective factor for OBL formation.

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.].

OCT Study of the Femtosecond Laser Opaque Bubble Layer

PURPOSE

To characterize the location and regularity of the opaque bubble layer (OBL) in the corneal stroma after femtosecond laser-assisted LASIK (FS-LASIK) flap generation.

METHODS

In this prospective study, 30 eyes of 15 patients who had FS-LASIK surgery for myopia, astigmatism, and/or hyperopia were included. Screen captures were obtained at the end of the flap creation and the eyes with hard type OBL were immediately imaged with anterior segment optical coherence tomography.

RESULTS

The mean age of the 9 men and 6 women was 40 ± 11.3 years (range: 22 to 60 years). Seven eyes (23.3%) developed hard type OBL that was typically localized in the central cornea beneath the LASIK flap and, in the majority of cases, located close to the hinge of the flap. Three of the seven eyes had OBL only within the laser cut, whereas the four other eyes had OBL in a spotty distribution within the stromal bed beneath the flap. None of the eyes had an accumulation of OBL within the flap itself.

CONCLUSIONS

The excimer laser ablation of a stroma with OBL may be different from that of a stroma without OBL. Management of OBL when it occurs due to flap production, including allowing the bubble to dissipate when they overlie the pupil, is important to obtain the best outcomes with femtosecond laser-assisted LASIK. [J Refract Surg. 2017;33(1):18-22.].

Comparison of efficacy, safety, and predictability of laser in situ keratomileusis using two laser suites

Purpose

The main aim of this study was to compare the efficacy, safety, and predictability of femtosecond laser-assisted in situ keratomileusis performed by two different laser suites in the treatment of myopia for up to 6 months.

Methods

In this two-site retrospective nonrandomized study, myopic eyes that underwent laser-assisted in situ keratomileusis using IntraLase FS 60 kHz formed group 1 and those using WaveLight FS200 femtosecond laser system formed group 2. Ablation was performed with Visx Star S4 IR and WaveLight EX500 Excimer lasers, respectively, in groups 1 and 2. Both groups were well matched for age, sex, and mean level of preoperative refractive spherical equivalent (MRSE). Uncorrected distance visual acuity, corrected distance visual acuity, and MRSE were evaluated preoperatively and at 1 week, 1 month, and 6 months after treatment.

Results

Fifty-six eyes of 28 patients were included in the study. At 6-month follow-up postop, 78.6% of eyes in group 1 and 92.8% of eyes in group 2 achieved an uncorrected distance visual acuity of 20/20 or better (P=0.252). 35.7% and 50% in group 1 and group 2, respectively, gained one line (P=0.179). No eye lost lines of corrected distance visual acuity. Twenty-five eyes in group 1 (92.7%) and 27 eyes in group 2 (96.3%) had MRSE within ±0.5 D in the 6-month follow-up (P>0.999). The mean efficacy index at 6 months was similar in group 1 and group 2 (mean 1.10±0.12 [standard deviation] vs 1.10±0.1) (P=0.799). The mean safety index was similar in group 1 and group 2 (mean 1.10±0.10 [standard deviation] vs 1.10±0.09) (P=0.407). Conclusion: The outcomes were excellent between the two laser suites. There were no significant differences at 6-month follow-up postop between the two laser systems.

Opaque Bubble Layer Risk Factors in Femtosecond Laser-assisted LASIK

PURPOSE

To determine the characteristics and risk factors for occurrence of opaque bubble layer (OBL) during femtosecond laser-assisted flap creation for LASIK.

METHODS

One hundred ninety-eight eyes of 102 consecutive patients who underwent LASIK flap creation performed with the Alcon WaveLight FS200 laser (Alcon Laboratories, Inc., Fort Worth, TX) were retrospectively analyzed in a cohort study. Preoperative manifest refraction, corneal keratometry, central corneal thickness, white-to-white corneal diameter, corneal hysteresis, corneal resistance factor, and programmed flaps parameters were collected. Digital images automatically recorded after flap creation were analyzed to measure OBL areas. Correlation tests were performed between preoperative corneal parameters and OBL areas.

RESULTS

The incidence rate of OBL was 48% (103 eyes). The mean OBL area as a percentage of the corneal flap area in the OBL group was 4.25% ± 7.16% (range: 0% to 32.9%). The central corneal thickness, corneal resistance factor, and corneal hysteresis were significantly positively correlated with the OBL area (r = 0.242, P = .001; r = 0.254, P = .028; and r = 0.351, P < .0001, respectively). Corneal hysteresis and OBL area were positively correlated, independently of the central corneal thickness and other confounder factors with standardized coefficient (r = 0.353 ± 0.227, P = .002).

CONCLUSIONS

This study confirms the already known OBL risk factors with a larger cohort and suggests for the first time that an elevated corneal hysteresis is an independent predictive risk for OBL occurrence.

Femtosecond lasers for laser in situ keratomileusis: a systematic review and meta-analysis

Purpose

The aim of this study was to review and meta-analyze whether there are differences between reported femtosecond (FS) lasers for laser-assisted in situ keratomileusis (LASIK) in terms of efficacy, predictability, and safety as primary outcomes and corneal flap thickness measurements and pre- and postoperative complications as secondary outcomes.

Methods

A comprehensive literature search of PubMed, Science Direct, Scopus, and Cochrane CENTRAL Trials Library databases was conducted to identify the relevant prospective randomized controlled trials of FS lasers for LASIK. Thirty-one articles describing a total of 5,404 eyes were included.

Results

Based on efficacy, IntraLase FS 10 and 30 kHz gave the best results. Based on predictability and safety, there were no differences between various FS lasers. FEMTO LDV and IntraLase FS 60 kHz produced the most accurate flap thicknesses. IntraLase and Wavelight SF200 had the fewest intraoperative complications. IntraLase, Visumax, and Wavelight FS200 had the most seldom postoperative complications.

Conclusion

There were dissimilarities between different FS lasers based on efficacy and intraoperative and postoperative complications. All FS lasers were predictable and safe for making corneal flaps in LASIK.

Anterior chamber gas bubble emergence pattern during femtosecond LASIK-flap creation

AIM

To characterise the emergence pattern of cavitation bubbles into the anterior chamber (AC) following femtosecond laser-assisted in situ keratomileusis (LASIK)-flap creation

METHODS

Retrospective review of patients undergoing femtosecond LASIK surgery at Boston Laser, a private refractive surgery practice in Boston, Massachusetts, between December 2008 and February 2014. Patient charts were reviewed to identify all cases with gas bubble migration into the AC. Surgical videos were examined and the location of bubble entry was recorded separately for right and left eyes.

RESULTS

Five thousand one hundred and fifty-eight patients underwent femtosecond LASIK surgery. Air bubble migration into the AC, presumably via the Schlemm's canal and trabecular meshwork, occurred in 1% of cases. Patients with AC bubbles had an average age of 33±8 years with a measured LASIK flap thickness of 96±21 μm. The occurrence of gas bubbles impaired iris registration in 64% of cases. Gas bubbles appeared preferentially in the nasal or inferior quadrants for right (92% of cases) and left (100% of cases) eyes. This bubble emergence pattern is significantly different from that expected with a random distribution (p<0.0001) and did not seem associated with decentration of the femtosecond laser docking system.

CONCLUSIONS

The migration of gas bubbles into the AC is a rare occurrence during femtosecond laser flap creation. The preferential emergence of gas bubbles into the nasal and inferior quadrants of the AC may indicate a distinctive anatomy of the nasal Schlemm's canal.

Longitudinal comparison of outcomes after sub-Bowman keratomileusis and laser in situ keratomileusis: randomized, double-masked study

PURPOSE

To compare the outcomes of sub-Bowman keratomileusis (100-μm flap) and laser in situ keratomileusis (LASIK) (120-μm flap) using 150-kHz femtosecond laser.

DESIGN

Randomized, double-masked, contralateral clinical trial.

METHODS

One hundred patients (200 eyes) with myopia or myopic astigmatism were included. Postoperative examinations were performed at week 1 and months 1, 3, 6, and 12. Main outcome measures included postoperative uncorrected (UCVA) and best-corrected distance visual acuity (BCVA); manifest refraction spherical equivalent; efficacy and safety indices; corneal thickness; and complications.

RESULTS

The mean age of patients was 33.9 ± 7.9 years. Overall, the preoperative UCVA, BCVA, and manifest refraction spherical equivalent were 1.349 ± 0.332, -0.022 ± 0.033, and -5.81 ± 1.61 diopters, respectively. No significant difference was observed in preoperative (P ≥ .226) or intraoperative parameters (P ≥ .452) between both groups, except residual stromal thickness (P < .001). The UCVA, manifest refraction spherical equivalent, and central corneal thickness stabilized by 1 week, while the thinnest corneal thickness stabilized by 3 months postoperatively. There was no significant difference between both groups for any parameter during all follow-up visits (P ≥ .132) except the 3-month safety index, which was better in the sub-Bowman keratomileusis group (P = .007). Soft opaque bubble layer was noted intraoperatively in 12 cases (7, 100-μm group; 5, 120-μm group; P = .577). No postoperative complications were observed.

CONCLUSIONS

Our study did not find any differences in the visual and refractive outcomes between femtosecond-assisted sub-Bowman keratomileusis and LASIK. Both surgeries resulted in quick visual recovery as early as 1 week postoperatively.

Incidence and Outcomes of Anterior Chamber Gas Bubble during Femtosecond Flap Creation for Laser-Assisted In Situ Keratomileusis

Purpose. To report the incidence and outcomes of anterior chamber gas bubble formation during femtosecond laser flap creation for laser-assisted in situ keratomileusis (LASIK). Methods. The charts of 2,886 consecutive eyes that underwent femtosecond LASIK from May 2011 through August 2014 were retrospectively reviewed. The incidence, preoperative characteristics, intraoperative details, and postoperative outcomes were analyzed in subjects developing anterior chamber gas bubble formation during the procedure. Results. A total of 4 cases (0.14%) developed anterior chamber gas bubble formation during femtosecond laser flap creation. In all four cases, the excimer laser was unable to successfully track the pupil immediately following the anterior chamber bubble formation, temporarily postponing the completion of the procedure. There was an ethnicity predilection of anterior chamber gas formation toward Asians (p = 0.0055). An uncorrected visual acuity of 20/20 was ultimately achieved in all four cases without further complications. Conclusions. Anterior chamber gas bubble formation during femtosecond laser flap creation for LASIK is an uncommon event that typically results in a delay in treatment completion; nevertheless, it does influence final positive visual outcome.

Prospective contralateral eye study to compare 80- and 120-μm flap LASIK using the VisuMax femtosecond laser

PURPOSE

To compare visual outcomes and flap stability of LASIK with ultrathin 80- and 120-μm flaps created with a VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) for moderate to high myopia and to evaluate the effect of corneal flap thickness on outcomes.

METHODS

In a prospective contralateral eye study, 36 consecutive patients (72 eyes) underwent bilateral LASIK for myopia ranging from -2.00 to -10.00 diopters using the VisuMax femtosecond laser and MEL-80 excimer laser (Carl Zeiss Meditec). One eye of each patient was randomized to have the 80-μm flap and the other to the 120-μm flap created with 200-kHz VisuMax femtosecond laser. Preoperative and postoperative tests included visual acuity, manifest refraction, contrast sensitivity, and flap thickness measured by anterior segment optical coherence tomography. Main outcomes and complications were checked at postoperative 1 week and 1, 3, and 6 months.

RESULTS

There were no differences in visual outcome, residual refractive error, or contrast sensitivity between groups during follow-up, except for better uncorrected visual acuity at postoperative 1 day in the 120-μm group. Mean standard deviations of measured flap thickness during follow-up ranged from 3.16 to 3.80 μm in both groups. Opaque bubble layer, a unique complication in femtosecond LASIK, was more frequent in the 80-μm group (7 of 36: 19%) than in the 120-μm flap group (3 of 36: 8%) without a statistically significant difference (P = .301) and was related to thicker central cornea and steeper keratometric value, although it did not influence clinical results. Comparison of the intended versus achieved correction showed no significant differences between groups.

CONCLUSIONS

LASIK using the VisuMax femtosecond laser supplied good clinical results and flap reproducibility in both the 80- and 120-μm flap groups. Patients with relatively thin cornea may benefit from 80-μm flap LASIK.

Essential opaque bubble layer elimination with novel LASIK flap settings in the FS200 Femtosecond Laser

Background

The purpose of this study is to evaluate the extent and incidence of opaque bubble layer (OBL) using laser-assisted in situ keratomileusis (LASIK) flaps created with the Alcon/WaveLight® FS200 femtosecond laser as a result of a recent change in flap programming parameters aiming to reduce further the incidence and extent of OBL.

Methods

Intraoperative digital images of flaps from 36 consecutive patients (72 eyes) subjected to bilateral femtosecond-assisted LASIK were analyzed using a proprietary computerized technique. The incidence and extent of OBL was measured and reported as a percentage of the entire flap area. Flap creation was performed with a 1.7 mm wide canal, implemented as an updated design intended to reduce the extent of OBL (group A). The same OBL parameters were investigated and compared in an age-matched and procedure-matched patients in whom the previous standard setting of a 1.3 mm wide canal was implemented (group B).

Results

In group A, the average extent of OBL was 3.69% of the flap area (range 0%–11.34%). In group B, the respective values were 6.06% (range 0%–20.24%). We found the difference to be statistically significant (one-tailed P = 0.00452).

Conclusion

This study suggests that there is a significant reduction in the incidence and extent of OBL when novel LASIK flap ventilation canal parameters of width and spot line separation are used.

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.

Digital analysis of flap parameter accuracy and objective assessment of opaque bubble layer in femtosecond laser-assisted LASIK: a novel technique

Background:

The purpose of this study was to determine flap parameter accuracy, extent of the opaque bubble layer, and incidence of skip lines in femtosecond laser-assisted stromal in situ keratomileusis (LASIK) using the WaveLight^® FS200 laser and optoelectronic clinical measurements.

Methods:

Images from 101 flaps were automatically recorded during consecutive routine LASIK procedures performed using the WaveLight FS200 femtosecond laser and the EX500 excimer laser. Digital processing of these images was used to evaluate objectively the diameter of FS200-created flaps, by comparing planned versus achieved procedures and to evaluate the incidence and extent (area) of the opaque bubble layer.

Results:

The intended flap diameters were between 8.00 mm and 9.50 mm. The achieved flap diameters showed extremely high precision, and were on average −0.16 ± 0.04 mm smaller for a 8.00 mm intended flap diameter, −0.12 ± 0.03 mm smaller for a 8.50 mm flap, and up +0.06 ± 0.06 mm wider for a 9.50 mm flap. With an average flap area of 72.4 mm², the mean area of the opaque bubble layer (4.1 ± 4.3 [range 0–14.34] mm²) corresponded to a 6% opaque bubble layer-to-flap area. Specifically, 80% of the femtosecond-created flaps had an essentially zero opaque bubble layer (<2.7% of the flap area).

Conclusion:

In our clinical experience, flaps created using FS200 and this novel highly objective assessment technique demonstrate both precision and reproducibility. The incidence of opaque bubble layer was minimal.

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.

In vivo structural characteristics of the femtosecond LASIK-induced opaque bubble layers with ultrahigh-resolution SD-OCT

The authors report in vivo morphology of opaque bubble layers with ultrahigh-resolution anterior-segment optical coherence tomography (UHR-OCT) in 3 patients. Two patients were operated on with a 30-kHz IntraLase femtosecond laser (Abbott Medical Optics, Abbott Park, IL) and one patient was operated on with a 500-kHz VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). UHR-OCT images from the patient operated on with the 500-kHz femtosecond laser revealed that the opaque bubble layer extended anterior to the flap dissection plane up to Bowman's membrane. The lamellar flap dissection was incomplete in this patient. The opaque bubble layer in the patients operated on with the 30-kHz femtosecond laser extended posterior to the flap dissection plane and these patients experienced complete lamellar dissections with uncomplicated flap lifts. UHR-OCT imaging can be used to demonstrate the structural characteristics of OBL. It has the potential to be used to predict incomplete lamellar flap dissections in patients with opaque bubble layers.

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.

Allopatric femtosecond laser gas-bubble formation in a closed system

PURPOSE

To test a possible mechanism for allopatric gas-bubble formation in femtosecond laser-assisted surgery using an experimental closed system.

SETTING

Bascom Palmer Eye Institute, University of Miami, Miami, Florida, USA.

METHODS

Plastic bottles were filled with balanced salt solution (BSS). Femtosecond laser (IntraLase) flap-mode cuts were made on the walls of the BSS bottles. After femtosecond laser application, the BSS bottles were viewed under the excimer laser microscope and the results photographed. Next, the BSS bottles and laser cuts were imaged with optical coherence tomography.

RESULTS

In-bottle gas bubbles were consistently produced in the closed system. No cut lines crossed the inner wall of the BSS bottles.

CONCLUSION

Results show that in situ gas-bubble formation as a mechanism for gas-bubble formation is a possible alternative to gas traveling through the anterior segment and into the intraflap laser space.