Laser In Situ Keratomileusis Flap Research Articles

Creation of a Corneal Flap for Laser In Situ Keratomileusis Using a Three-Dimensional Femtosecond Laser Cut: Clinical and Optical Coherence Tomography Features

Laser in situ keratomileusis (LASIK) is the most frequently used technique for the surgical correction of refractive errors on the cornea. It entails the creation of a superficial hinged corneal flap using a femtosecond laser, ablation of the underlying stromal bed using an excimer laser, and repositioning of the flap. A corneal flap with an angled side cut reduces the risk of flap dislocation and infiltration of epithelial cells and confers unique biomechanical properties to the cornea. A new laser software creating three-dimensional (3D) flaps using a custom angle side cut was retrospectively evaluated, comparing optical coherence tomography 3D (with intended 90° side cut) and 2D flaps (with tapered side cuts) as well as respective intra- and early postoperative complications. Four hundred consecutive eyes were included, two hundred for each group. In the 3D group, the mean edge angle was 92°, and the procedure was on average 5.2 s slower (p = 0). Non-visually significant flap folds were found in thirteen eyes of the 2D group and in seven eyes of the 3D group (p = 0.17). In conclusion, the creation of a LASIK flap using a 3D femtosecond laser cut, although slightly slower, was safe and effective. The side cut angle was predictable and accurate.

Salzmann's Nodular Degeneration in Refractive Surgery: The Earlier Hit Hypothesis of EBM Injury-Related Fibrosis of the Subepithelial Space and Deeper Corneal Extension.

To review the atypical development of Salzmann's nodular degeneration (SND) after two cases of laser in situ keratomileusis (LASIK) and one case of photorefractive keratomileusis (PRK), and to highlight the pathophysiology of SND and its treatment. Three cases of SND (two following LASIK performed with microkeratomes and one following PRK) were reviewed and Pubmed.gov and internet searches were performed. SND is myofibroblast-generated fibrosis in the subepithelial space between the epithelium and Bowman's layer that develops years or decades after traumatic, surgical, infectious, or inflammatory injuries to the cornea in which the epithelial basement membrane is damaged in one or more locations and does not fully regenerate. It is hypothesized based on these cases, and the previous immunohistochemistry of other investigators, that myofibroblast precursors, such as fibrocytes or corneal fibroblasts, that enter the subepithelial space are driven to develop into myofibroblasts, which slowly proliferate and extend the fibrosis, by transforming growth factor-beta from epithelium and tears that passes through the defective epithelial basement membrane. These myofibroblasts and the disordered collagens, and other extracellular matrix components they produce, make up the subepithelial opacity characteristic of SND. Nodules are larger accumulations of myofibroblasts and disordered extracellular matrix. If the injury is associated with damage to the underlying Bowman's layer and stroma, as in LASIK flap generation, then the myofibroblasts and fibrosis can extend into Bowman's layer and the underlying anterior stroma. SND fibrosis often extends into Bowman's layer and the anterior stroma if there are associated Bowman's defects, such as incisions or lacerations. In the latter cases, SND frequently cannot be removed by simple scrape and peel, as typically performed for most common SND cases, but can be trimmed to remove the offending tissue. This condition is more accurately termed Salzmann's subepithelial fibrosis. [J Refract Surg. 2024;40(5):e279-e290.].

Traumatic flap dehiscence 15 years after LASIK: case report and review of the literature

Introduction: Corneal flap trauma rarely occurs years after laser in situ keratomileusis (LASIK), and management is not standardized. The authors report a case of LASIK flap dehiscence 15 years postoperatively with a review of the literature describing clinical characteristics, management, and outcomes of similar cases occurring at least 6 years postoperatively. Patient and Clinical Findings: A 55-year-old man with a history of LASIK surgery 15 years prior presented with flap dehiscence after trauma with a tree branch. His right eye uncorrected distance visual acuity (UDVA) at presentation was counting fingers. On slitlamp examination, the medial flap edge was folded underneath the temporal aspect. Diagnosis, Intervention, and Outcomes: The flap was unfolded, irrigated, repositioned, and instilled with topical antibiotics. The patient was started on prednisolone acetate 1% and moxifloxacin. On postoperative day 1, his UDVA improved to 20/50 and the flap remained centered and clear. His vision stabilized at 20/30 after 7 months. Peripheral epithelial ingrowth was noted without visual axis obscuration. Conclusions: This case, along with 20 reported instances of late traumatic flap dehiscence, highlights that early recognition with prompt intervention can optimize visual outcomes. Comparison of injury mechanisms, treatments, and complications may guide surgeons in patient counseling and care.

Outcomes of Flap Amputation After Laser In Situ Keratomileusis.

The aim of this study was to describe the indications and outcomes of flap amputation after laser in situ keratomileusis (LASIK) at a referral-based institution. In this retrospective consecutive case series, medical records of patients who underwent LASIK flap amputation at Mayo Clinic, Rochester, MN, between January 1, 1998, and January 31, 2023, were reviewed. Fifteen eyes (15 patients) underwent flap amputation during the study period. The median age was 45 years (range, 25-71 years), and 8 patients (53%) were men. The median uncorrected visual acuity before flap amputation was 20/200 (range 20/40-hand motions). Indications for flap amputation included epithelial ingrowth (n = 6, 40%), infectious keratitis (n = 6, 40%), diffuse lamellar keratitis (n = 1, 7%), vegetative foreign body (n = 1, 7%), and astigmatism from fixed flap striae (n = 1, 7%). The median duration of follow-up was 8 months (range 1-234 months). Subsequent corneal interventions included chelation of calcific band keratopathy (n = 1, 7%), lamellar keratoplasty (n = 1, 7%), penetrating keratoplasty (n = 2, 18%), keratoprosthesis (n = 1, 7%), and rigid contact lens wear (n = 4, 27%). The final median best visual acuity was 20/25 (range 20/20-20/200). Compared with noninfectious indications for flap amputation, eyes with infectious indications had worse baseline median uncorrected visual acuity (hand motions vs. 20/63, P < 0.001), were more likely to undergo major corneal surgical intervention (50% vs. 11%), and had worse final median best visual acuity (20/50 vs. 20/20, P = 0.018). LASIK flap amputation is sometimes necessary to control threatening corneal diseases. Excellent visual outcomes were achieved in most cases, albeit with additional intervention or rigid contact lens wear.

Incidence of Microfolds Using a Standardized Three-Stage LASIK Flap Replacement Protocol.

To describe a standardized three-stage flap replacement protocol and report the incidence of microfolds after femtosecond laser-assisted laser in situ keratomileusis (LASIK) surgery. A retrospective analysis of 14,374 consecutive LASIK procedures with the VisuMax femtosecond laser (Carl Zeiss Meditec) by two surgeons was conducted. As per the standardized procedure, all eyes underwent the three-stage flap replacement protocol consisting of controlled standardized minimal irrigation and flap repositioning after ablation, followed by fluorescein-controlled slit-lamp adjustments and slit-lamp adjustments on day 1 (if required). Microfold incidence was recorded at all subsequent visits and recorded by independent observers classified using a standardized 6-point grading system including whether they were refractively or visually significant. Flap thickness used was 80 to 89 µm (7.2%), 90 to 99 µm (51.7%), 100 to 109 µm (17.8%), and 110 to 130 µm (23.2%). Slit-lamp adjustment at day 1 was performed in 956 eyes (6.77%), with the highest incidence in 80 to 89 µm flaps (27.6%). A flap slip occurred in 23 eyes (0.16%) and was managed at the slit lamp for 21 eyes and in the operating room for 2 eyes. At 3 months after surgery, trace microfolds were present in 158 eyes (1.10%), grade 1 in 26 eyes (0.184%), and grade 2 in 2 eyes (0.016%). Grade 1 microfold incidence per flap thickness group was 39.1% for 80 to 89 µm, 30.4% for 90 to 99 µm, 13% for 100 to 109 µm, and 17.4% for 110 to 130 µm. No eyes required a flap lift for microfolds in the operating room. Multivariate regression analysis found microfold incidence to be higher for thinner flaps, higher correction, and larger optical zone. The three-stage protocol for flap positioning and management resulted in a low incidence of clinically visible microfolds and no visually significant microfolds. Day 1 slit-lamp adjustment was required more frequently in ultra-thin 80 to 89 µm flaps. [J Refract Surg. 2023;39(6):388-396.].

Interface Fluid Syndrome After Descemet Membrane Endothelial Keratoplasty in Patients With History of LASIK.

The aim of this study was to evaluate the visual, pachymetric, tomographic, and biomicroscopic findings in a series of cases with laser in situ keratomileusis (LASIK) flap interface fluid syndrome (IFS) after Descemet membrane endothelial keratoplasty (DMEK). Six cases were included in this study; all patients had a history of LASIK and underwent DMEK for the treatment of bullous keratopathy. After uneventful surgery, all patients presented with corneal edema and IFS under the LASIK flap, which was demonstrated with anterior segment optical coherence tomography (AS-OCT). Visual acuity, clinical findings, pachymetry, endothelial cell count, and AS-OCT were documented during the management of these cases. IFS appears 2.33 days (±1.03) after DMEK. One case improved with conservative treatment. In 5 cases, the LASIK flap was lifted, the fluid was drained, and the flap was replaced. The mean best-corrected visual acuity after fluid drainage was 0.44 logMAR (range 0.18-1.0) and mean central corneal thickness was 538 μm ± 160. Total resolution of the IFS was achieved at 14.5 days (range 4-30) after DMEK. AS-OCT showed resolution of the flap interface in 5 of 6 cases, while 1 patient required second DMEK due to reaccumulation of the interface fluid. IFS can occur after DMEK in patients with previous LASIK. AS-OCT is a valuable tool for monitoring these cases preoperatively and postoperatively. Early surgical management is often needed to achieve resolution.

Epithelial cell curette: simple solution to epithelial cell removal from small-incision lenticule extraction pocket or LASIK flap

Epithelial ingrowth is one of the complications associated with refractive laser surgery. Although treatment is relatively simple following laser in situ keratomileusis (LASIK), the inaccessibility of the pocket makes treatment following small-incision lenticule extraction (SMILE) somewhat difficult. An innovative scraping tool that features a biconcave curette tip allows for the manual removal of epithelial cells from the SMILE pocket without flushing or conversion to a flap. The tool can also be used to remove cells from beneath the LASIK flap without performing a complete relift.

Epithelial Ingrowth Under LASIK Flap After a Massive Shockwave From the Port of Beirut Ammonium Nitrate Explosion

PURPOSE: To present a case of epithelial ingrowth under a laser in situ keratomileusis (LASIK) flap as a direct result of a pressure shockwave without direct blunt trauma to the eye. METHODS: Case report RESULTS: A 27-year-old woman developed epithelial in-growth under the LASIK flap interface after a massive shock-wave trauma to the eye caused by the 2020 Port of Beirut explosion. No flap dislocation, folds, or tears had been noted on examination after the trauma. Observation with close follow-up was elected. The vision and area of ingrowth remained stable over 1 year of follow-up. CONCLUSIONS: Pressure shockwave from an immense blast can mimic direct blunt trauma in eyes after LASIK and can result in epithelial ingrowth. Treatment should be tailored to vision, flap condition, and progression. [J ournal of Refractive Surgery Case Reports. 2022;2(2):e26–e28.]

Delayed Laser In Situ Keratomileusis Interface Haze 6 Months After Corneal Cross-linking for Ectasia

PURPOSE: To report a case of delayed subepithelial haze at the laser in situ keratomileusis (LASIK) flap interface after corneal cross-linking (CXL) for LASIK-induced ectasia. METHODS: A 39-year-old woman with ectasia after LASIK underwent accelerated CXL with riboflavin and hydroxypropyl methylcellulose every 2 minutes for 20 minutes, then ultraviolet light at a fluence of 10 mW/cm 2 for 9 minutes. Outcomes measured included stromal haze assessment and visual refractive parameters. Follow-up was conducted using slit-lamp imaging, optical coherence tomography (OCT), corneal topography, and a dedicated OCT image analysis software. RESULTS: Six months after CXL, OCT of the right eye showed a sharply demarcated hyperreflective linear lesion inferotemporal to the corneal center, at the LASIK flap interface. The haze was 1.5-mm wide with 12.49 grayscale units (GSU) intensity and involved the anterior stroma at 0.9 mm away from the center extending from 225° to 255°. This haze peaked at 9 months after CXL, reaching 3 mm in size and 29.01 GSU in intensity. Corneal topography showed steepening on the haze area and flattening on the diametrically opposite side. Topical steroid therapy was initiated. At final evaluation (19 months), there was a significant decrease in haze reflectivity and size, accompanied by marked improvement of the topography. CONCLUSIONS: Delayed corneal haze after CXL with a history of LASIK can develop at the level of the LASIK interface right under the cone area. Although it was responsive to topical steroid therapy, the reasons for this clinical presentation are still unknown. [ Journal of Refractive Surgery Case Reports. 2022;2(2):e46–e50.]

Efficacy and Safety of Surgically Managed Late Traumatic LASIK Flap Displacements in a Study of 66 Cases.

To evaluate safety and efficacy in the management of flap displacement after laser in situ keratomileusis (LASIK) and subsequent complications. This was a retrospective study performed using data recorded at the center's database from October 2002 to August 2021. Efficacy and safety were both converted to binary outcomes (loss of one or more lines and no change or gain in lines of visual acuity). The effects of time from surgery to complication and from complication to repair were assessed and the odds ratios and probabilities were calculated. The same procedure was applied to investigate the effect of these temporal variables on complications. A total of 66 eyes with late traumatic LASIK flap displacements were studied. Efficacy remained unchanged in 48 patients (64 eyes, 75%), and safety remained unchanged in 53 patients (59 eyes, 90%). Sixty-six patients (64 eyes, 100%) achieved visual acuity values of 20/40 and 45 patients (64 eyes, 70.3%) achieved values of 20/20. The flap displacement was resolved in the first 24 hours (SD ± 0.1 days). Surgery was performed in 58 patients (65 eyes, 90%). Epithelial ingrowth was the most frequent complication. Patients who underwent surgery tended not to lose lines (P = .05). The risk of developing epithelial ingrowth increases with time after LASIK surgery until traumatic flap displacement (odds ratio: 1.001; P < .001). The prevalence of dislocation during the study period was 0.012%. Visual safety values were favorable after resolution of the flap complication. Immediate surgical management leads to better visual efficacy, and the time between LASIK and trauma increases the risk of epithelial ingrowth after flap displacement. [J Refract Surg. 2022;38(4):270-276.].

Effect of suction on the posterior segment after LASIK using Femtosecond Laser vs Microkeratome

Background: Creating a successful corneal flap is the first critical step during LASIK surgery. Two techniques are used to produce corneal flaps during LASIK surgery: a microkeratome or a femtosecond laser. Femtosecond laser has a significant impact on refractive surgery by enabling non-mechanical creation of corneal flaps during laser in situ keratomileusis (LASIK). During LASIK flap creation, intraocular pressure (IOP) increases to levels exceeding 65 mm Hg. Femtosecond laser flap creation exerts less extreme IOP fluctuations but requires more procedural time than when a microkeratome is used. This study was conducted upon 60 eyes of 38 patients to evaluate the effect of applied suction during LASIK procedures on the posterior segment of myopic eyes, whether the flap was created by Microkeratome or Femtosecond laser. The study subjects were equally divided into 2 groups: group F (30 eyes of 20 patients) underwent femtosecond laser-assisted LASIK surgery and group M (30 eyes of 18 patients) underwent microkeratome-assisted LASIK surgery using Moria M2 for the treatment of myopia. It was found that the central macular thickness and RNFL thickness were not changed significantly in both groups when measured 1 week after surgery. Regarding the incidence of PVD, there was a higher incidence in group F, it was detected in 8 eyes (26.7%) compared to group M, it was detected in 1 eye (3.3%). Conclusion: Slight localized changes of macular thickness and reduction of the RNFL thickness were caused by LASIK using the two major forms of flap creation, namely a microkeratome or a femtosecond laser. Regarding the incidence of PVD, it was found that femtosecond laser-assisted LASIK using Visumax femtosecond laser had a higher incidence than that after microkeratome-assisted LASIK with the Moria M2. So the surgery of LASIK is safe and efficient, but surgeons should choose effective and safe suction mode, shorten the suction time and exclude potential retinopathy and pre-existing glaucoma before surgery to improve the safety and efficacy of LASIK.

Interface Fluid Syndrome After Descemet Membrane Endothelial Keratoplasty

PURPOSE: To describe a case of interface fluid syndrome in a patient with a remote history of laser in situ keratomileusis (LASIK) and recent staged cataract surgery and Descemet membrane endothelial keratoplasty (DMEK). METHODS: A 65-year-old man presented with visual impairment in the left eye in the setting of Fuchs' endothelial dystrophy and cataract. Cataract surgery followed by DMEK 3 months later were performed in the left eye. RESULTS: Following DMEK, a cleft of interface fluid was documented at the LASIK flap interface via anterior segment optical coherence tomography (AS-OCT) 4 days postoperatively. The DMEK graft was fully attached and intraocular pressure (IOP) was low to normal when the interface fluid was first observed. This interface fluid persisted despite management with IOP-lowering drops. IOP consistently measured low, and the DMEK graft subsequently detached inferiorly. The decision was made to perform Descemet stripping automated endothelial keratoplasty (DSAEK), after which the interface fluid resolved and visual acuity improved significantly. CONCLUSIONS: Interface fluid syndrome can occur years after LASIK, especially following intraocular surgery. This patient may have developed interface fluid syndrome following DMEK due to endothelial dysfunction in the setting of DMEK graft incompetence. Resolution of interface fluid in this patient was achieved after DSAEK. [ Journal of Refractive Surgery Case Reports. 2021;1(1):e15–e18.]

Brillouin microscopic depth-dependent analysis of corneal crosslinking performed over or under the LASIK flap.

To determine the impact of corneal crosslinking (CXL) performed over the laser in situ keratomileusis (LASIK) flap using the Standard CXL (S-CXL) protocol or under the flap after flap lift (flap-CXL) on regional corneal stiffness using Brillouin microscopy. University of Southern California Keck School of Medicine, Los Angeles, California, and Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA. Laboratory ex vivo experiment. After epithelium debridement, LASIK flaps were created on intact fresh porcine eyes with a mechanical microkeratome. Then, S-CXL (riboflavin applied to the corneal surface followed by 3 mW/cm ultraviolet exposure with the flap in place for 30 minutes) or flap-CXL (riboflavin applied to the stromal bed after reflecting the flap followed by the same ultraviolet A exposure with the flap replaced) was performed. Depth profile of stiffness variation and averaged elastic modulus of anterior, middle, and posterior stroma were determined by analyzing Brillouin maps. Each eye served as its own control. The study was performed on 24 fresh porcine eyes. S-CXL had maximal stiffening impact in the anterior most corneal stroma within the LASIK flap (8.40 ± 0.04 GHz), whereas flap-CXL had lower maximal stiffening impact (8.22 ± 0.03 GHz) (P < .001) that occurred 249 ± 34 μm under the corneal surface. S-CXL increased longitudinal modulus by 6.69% (anterior), 0.48% (middle), and -0.91% (posterior) as compared with flap-CXL, which increased longitudinal modulus by 3.43% (anterior, P < .001), 1.23% (middle, P < .1), and -0.78% (posterior, P = .68). The S-CXL technique generated significantly greater stiffening effect in the anterior cornea than a modified protocol with riboflavin administration under the flap (flap-CXL). Minimal stiffening occurred in the middle or posterior cornea with either protocol.

Analysis of corneal stromal roughness after iFS 150 kHz and LenSx femtosecond LASIK flap creation in porcine eyes.

To describe and compare the stromal bed roughness obtained after laser in situ keratomileusis (LASIK) flap creation using a corneal femtosecond laser platform (iFS 150) and a "dual" femtosecond (FS) laser platform (LenSx). This ex vivo experimental study was conducted in an animal model using 12 freshly enucleated porcine eyes, six with each femtosecond laser. The standard laser treatment parameters were used for the experiment. After LASIK flap creation, the corneal stromal roughness was assessed using atomic force microscopy (AFM) in contact mode immersed in liquid. In each sample, surface measurements were obtained in 60 regions of six eyes per FS laser in 10 20 × 20-micron areas of the central corneal stroma at 512 × 512-point resolution. The surface roughness was measured and the root-mean-square (RMS) values of the roughness were obtained. The mean RMS ± standard deviation values were 430 ± 150 nm for the corneal femtosecond laser platform and 370 ± 100 nm for the dual FS laser platform (P < 0.011). In this experimental study with AFM, we found smoother stromal beds after LASIK flap creation with LenSx compared to iFS 150 kHz. Further studies are needed to understand visual implications of the differences found.

Corneal Ectasia Risk And Percentage Tissue Altered In Myopic Patients Presenting For Refractive Surgery.

PurposeA percentage tissue altered (PTA) score of ≥40% has been advocated as an independent indicator of post-operative ectasia risk following laser in-situ keratomileusis (LASIK). This study was performed to test the hypothesis that refractive procedures, such as laser-assisted sub-epithelial keratectomy (LASEK) or small incision lenticule extraction (SMILE), may alter the range of PTA, within which refractive corneal surgery can be safely performed.SettingRefractive department, tertiary ophthalmic hospital.DesignRetrospective observational study.MethodsReview of case notes was performed for patients who presented for refractive surgeries, other than LASIK. To determine the risk of corneal ectasia for each patient prior to refractive surgery, we estimated what each patient’s PTA would have been if they had undergone LASIK. The Randleman Ectasia Risk Score System (ERSS) was also calculated.Results114 eyes (66 patients) were included. 94 eyes underwent SMILE. 20 eyes underwent LASEK. A significant proportion of eyes had PTA ≥40% – SMILE eyes: up to 31.9%, LASEK eyes: up to 60.0% (at presumed LASIK flap of 120 μm). The maximum calculated PTA was up to 47.9% in the SMILE group and up to 51.5% in the LASEK group. Using ERSS, 12.8–16% of SMILE eyes and 15.0–80.0% of LASEK eyes would have been considered to have moderate-to-high ectasia risk. No post-surgical ectasia was observed at 3 years.ConclusionSMILE and LASEK alter the range of PTA, within which corneal refractive surgery may be performed with a lower risk of developing post-operative corneal ectasia; a safe PTA threshold needs to be determined for these procedures before recommendations for clinical practice can be made.

Laser flap enhancement 5 to 9 years and 10 or more years after laser in situ keratomileusis: Safety and efficacy

To study the safety and efficacy of refractive enhancement by flap lifting 5 and 10 years after laser in situ keratomileusis (LASIK). Vissum Alicante, Spain. Retrospective case series. Eyes with a flap lift at least 5years after primary LASIK with a 3-month follow-up were evaluated. The primary outcome measures were safety and the complication rate. Moderate epithelial ingrowth was managed with Nd:YAG laser treatment. The primary LASIK procedure was myopic in 45 eyes, hyperopic in 22 eyes, and presbyopic in 3 eyes. The mean time from primary LASIK to the flap lift was 12.3years±3.45 (SD). In 57 eyes, the primary LASIK flap was created at least 10years before the enhancement. The mean pre-lift spherical equivalent was -1.29±1.23 diopters (D) in the myopia group and +0.65±1.72 D in the hyperopia group. Three months later, 88% of eyes and 74% of eyes, respectively, had an uncorrected distance visual acuity of 20/20 or better; 100% achieved at least 20/25. No eye lost 2 lines or more of corrected distance visual acuity. In the myopia group, the efficacy index was 0.94 and the safety index was 0.98 at 6months. Mild epithelial ingrowth developed in 31.43% of eyes and clinically significant epithelial ingrowth in 11.42% of eyes; 4.28% required a relift for severe epithelial ingrowth. Late flap lift for refractive enhancement 10years or more after LASIK provided good efficacy and safety with fast visual recovery. The rate of surgical intervention for significant postoperative epithelial ingrowth was low.

Comparison of corneal flap striae and displacement after LASIK with microkeratome and femtosecond laser

Objective To compare the early corneal flap striae and displacement between mechanical microkeratome and femtosecond laser for laser in-situ keratomileusis (LASIK). Methods The data of 5 792 cases with LASIK from Jan. 2016 to Jan. 2017 were analyzed retrospectively. All cases were randomly divided into two groups: group A received flap made by femtosecond laser in 3 358 cases and group B received flap made by mechanical microkeratome in 2 434 cases. Patients with flap striae and displacement above grade Ⅱ without obvious trauma history in the early postoperative periods were selected as research objects, the incidence rate and causes were compared between the two groups. Results The corneal flap striae and displacement occurred in 15 eyes (0.45 %) in group A and 22 eyes (0.90 %) in group B. The difference was statistically significant (χ2=4.647, P=0.031). The spherical equivalent of patients with corneal flap striae and displacement before surgery was (-7.71±1.38)D in group A and (-5.56±1.90)D in group B (t=-3.99, P=0.0003). The mean corneal flap thickness of patients with corneal flap striae and displacement was (84.29±5.78)μm in group A and (93.96±7.47)μm in group B. The difference of corneal flap thickness in two groups were not statistically significant between the displacement cases and the normal cases (t=0.34, P=0.73; t=-0.38, P=0.71). Conclusion The rate of corneal flap striae and displacement is related to the preoperative refraction and surgical method, but is not significant correlation with the thickness of the corneal flap. Femtosecond LASIK flaps represent significant improvement in predictability with implications for safety. Key words: Keratomileusis, laser in situ(LASIK); Flap creation, femtosecond laser-assisted; Flap creation, mechanical micro-keratome-assisted; Striae, corneal flap; Displacement, corneal flap

Intraocular pressure rises during laser in situ keratomileusis: Comparison of 3 femtosecond laser platforms

To measure intraocular pressure (IOP) elevations in porcine eyes during laser insitu keratomileusis (LASIK) performed using 3femtosecond laser platforms. Clínica Novovisión, Madrid, Spain. Experimental study. Three femtosecond devices, the iFS 150kHz, which is the newest-generation IntraLase with a flat interface, and the Victus and LenSx, which are both dual femtosecond lasers with curved interfaces, were used to create lamellar corneal flaps in freshly enucleated porcine eyes. The IOP was recorded during placement of the suction ring on the eye (suctioning phase) and during the intrastromal laser application for flap creation (cutting phase) using a manometric technique with direct cannulation to the anterior chamber. Twenty-one eyes were analyzed (7 per group). The mean IOP increase during suctioning was significantly higher with the iFS system (78.14mm Hg±23.6 [SD]) than with the Victus system (20.28±6.7mm Hg) (P=.0001). The LenSx system performed the suctioning and applanation phases simultaneously, making it impossible to obtain the results of the suctioning phase alone. The mean IOP elevation during the cutting phase was significantly lower with the LenSx system (20±5.3mm Hg) than with the iFS (108.1±17.0mm Hg) and Victus (96.4±16.8mm Hg) systems (P=.0001). The total surgical time was significantly lower with the LenSx system (17.21±0.7seconds) than with the iFS (25.10±4.3seconds) and Victus (33.40±0.7seconds) systems (P=.0001). The preliminary results suggest that the iFS and Victus systems induced higher IOP increases and required longer surgical times to cut a LASIK flap than the LenSx system.

Femtosecond-assisted LASIK flaps resistant to lift secondary to corneal epithelial defects: Case reports and ex vivo studies

To evaluate why epithelial defects created before femtosecond laser ablation result in laser insitu keratomileusis (LASIK) flaps resistant to lift. Boston Eye Group, Brookline, Massachusetts, USA. Case reports and exvivo studies. To examine the mechanism of resistance to flap lift after epithelial defects, flap creation with a femtosecond laser was performed in 30 fresh porcine eyes. Before ablation, the eyes were assigned to 3 groups. Group 1 was a control group with intact corneal epithelium. In Group 2, a central 2.0mm corneal epithelial defect was created by marking it with a 2.0mm trephine. In Group 3, a peripheral 2.0mm epithelial defect was created similarly. After the femtosecond laser procedure was performed, the flaps were lifted and the resistance to lift was documented. The corneas werefurther examined using anterior segment optical coherence tomography. In Group 1, no resistance was felt during flap lifts. In Group 2, significant resistance was encountered at the edge of the epithelial defects and the flaps could not be lifted in 7 of 10 eyes. In Group 3, similar significant resistance was encountered in all 10 eyes. Six of 10 flaps could not be lifted. Anterior segment optical coherence tomography from a representative cornea from Group 2 demonstrated a deeper dissection plane in the area where the overlying epithelium was missing. Epithelial defects can interfere with proper LASIK flap creation with the femtosecond laser. This seems to be attributable to a deeper cutting plane under the area of the epithelial defects compared with the surrounding area with intact epithelium.

Relevance of Swept-Source Anterior Segment Optical Coherence Tomography for Corneal Imaging in Patients With Flap-Related Complications After LASIK

To evaluate the role of swept-source anterior segment optical coherence tomography (AS-OCT) in the diagnosis and management of laser in situ keratomileusis (LASIK) flap-related complications. This prospective study included 25 eyes with LASIK flap-related complications imaged using swept-source AS-OCT between February and August 2016 at Alforsan Eye Centre, Assiut, Egypt. The images were acquired using a 6-mm line scan. Imaging of flap-related LASIK complications using AS-OCT revealed specific and nonspecific findings. Of note, epithelial ingrowth appeared as highly reflective lesions below the LASIK flap in the form of islands, nests, or a continuous sheet with or without changes in the overlying flap. Macrostriae manifested as dome-shaped irregularities on the stromal surface with regular overlying epithelium, whereas microstriae appeared as corrugations on the stromal surface with regular overlying epithelium. Less common complications included multiple flap macrostriae accompanied by a traumatic folded flap with a flap edge at the interface. Interface debris appeared as a highly reflective interface lesion with or without a surrounding reaction. One eye with a flap that was torn and lost intraoperatively showed epithelialization over a thin residual stroma underlying a contact lens with no stromal infiltration on the second postoperative day. AS-OCT was useful for the assessment of flap thickness and planning of the new flap thickness in the event of an incomplete cut. Swept-source AS-OCT is useful not only for diagnosis but also for management of eyes with LASIK flap-related complications by allowing noninvasive, noncontact, real-time acquisition of cross-sectional AS images.