LASIK Flap Research Articles

Assessment of Laser in Situ Keratomileusis Flap Predictability by Laser and Moria Microkeratome

Objective: In the present study, we compared LASIK flap thickness predictability created by a FS laser versus a Moria microkeratome in Mongolian patients. Methods: A total of ninety-six candidates for the LASIK procedure were stratified into two groups: FS laser-assisted and MK flap creation. Flap thickness was determined at five points. The side-cut angle was measured in three directions at the margin interface. LASIK flap assessment was performed one month postoperatively by Spectralis anterior segment optical coherence tomography. Results: Ninety-five participants (190 eyes) were recruited; 190 eyes were stratified to the FS group and 78 eyes to the MK group. The FS group had relatively even flap configurations, and the MK group had meniscus-shaped flaps. Regarding CR-sphere and cylinder, there was significant difference between 2 groups. The mean cylinder was -1.216 ± 0.924 in FS group while it was -0.730 ± 0.738 in MK group. Similarly, the mean sphere was -3.635 ± 2.031 in FS-LASIK group and -2.984 ± 1.502 in MK-LASIK group. The side-cut architecture varied among the two groups. OCT-C and OCT1Temporal values were significantly different between two groups. Conclusion: Improving the predictability of LASIK flap thickness and morphology is significantly important.

Epithelial ingrowth under LASIK flaps: tips and tricks for preventing recurrence!

LASIK for refractive error correction has become a universal surgery. Despite its popularity, the estimated prevalence of traumatic flap dislocations in post-LASIK patients is 3.9%, and it is sometimes associated with epithelial ingrowth. The prognosis in such cases depends on the rapid surgical revision of the flap with the removal of the EI and perioperative steps to prevent Epithelial ingrowth (EI) recurrence in the future. The video aims to display the steps involved in revising the flap, removing EI, and tips to prevent its recurrence. A 33-year-old post-LASIK patient presented with decreased vision, photophobia, and glare during the COVID pandemic in the right eye for 2 months. The best-corrected visual acuity was reduced to 6/60. The anterior segment revealed traumatic flap dislocation along with macro fold temporally and epithelial ingrowth. She underwent a successful flap revision surgery with no recurrence of epithelial ingrowth postoperatively. A successful revision of a 2-month-old traumatic folded flap was performed along with the complete removal of EI. It explains the step-by-step approach to avoid the recurrence of EI in each step of the surgical revision of the flap. The video is self-explanatory and guides novice surgeons too. https://youtu.be/JuOSjhrfw0g.

Traumatic LASIK Flap Avulsion Replaced by the Patient With Rotational Misalignment and Epithelial Ingrowth: Case Report

Traumatic LASIK Flap Avulsion Replaced by the Patient With Rotational Misalignment and Epithelial Ingrowth: Case Report

LASIK Flap Dislocation Masquerading as Corneal Abrasion: Lessons and Pearls

LASIK Flap Dislocation Masquerading as Corneal Abrasion: Lessons and Pearls

Novel Technique to Improve the Efficacy of Corneal Cross Linking in Cases of Post LASIK Ectasia.

The aim of the present study was to validate the use of a novel technique that can improve the efficacy of corneal cross-linking (CXL) in cases with post LASIK ectasia. This is a retrospective, comparative study that was conducted on patients who sought medical advice at Ain Shams University Hospitals and Maadi Eye Subspeciality Center, Cairo, Egypt. It included two groups of patients with post LASIK ectasia. Group 1 included patients who performed our proposed protocol (topo-guided PRK, followed by customized phototherapeutic keratectomy "PTK" to transmit the laser treatment to the corneal stroma, then CXL). For group 2, accelerated CXL was performed. Subjective refraction and relevant topographic/tomographic parameters (Sirius topographer) compared between the two groups. Recorded follow-ups included the 2 to 3-month follow-up visit and the last visit (mean ± SD of 17.2 months ± 10.2). Patients of group 1 (22 eyes of 22 patients) experienced significant improvements in most of the evaluated parameters at the 2- to 3-month follow-up visit and showed stability of the ectatic condition at the last follow-up visit, whereas patients of group 2 (10 eyes of 10 patients) showed stability of their ectatic condition at the 2- to 3-month follow-up visit, and one patient developed ectasia progression at the last follow-up visit. The present study validates the use of our novel protocol in cases having post LASIK ectasia with proven efficacy, safety, and stability, providing regularization for the corneal surface while simultaneously avoiding the unnecessary loss of cross-linking effect within the LASIK flap that no longer shares in the corneal biomechanical strength.

Erratum to: Consultation Section: Refractive. Early LASIK flap displacement without signs of infection. Edited by Germana M.Q.V. Pinto, MD, Lycia P. Sampaio, MD, Marcony R. Santhiago, MD, PhD. J Cataract Refract Surg 2022;48:863-868.

Erratum to: Consultation Section: Refractive. Early LASIK flap displacement without signs of infection. Edited by Germana M.Q.V. Pinto, MD, Lycia P. Sampaio, MD, Marcony R. Santhiago, MD, PhD. J Cataract Refract Surg 2022;48:863-868.

Safety and Precision of Two Different Flap-morphologies Created During Low Energy Femtosecond Laser-assisted LASIK.

Currently, two major principles exist to create LASIK flaps: firstly, a strictly horizontal (2D) cut similar to the microkeratome-cut and secondly an angled cut with a "step-like" edge (3D). The strictly horizontal (2D) cut method can be performed using apparatus such as the low-energy FEMTO LDV Z8 laser and its predecessors which are specific to this type. Alternatively, the low-energy FEMTO LDV Z8 laser's 3D flap design creates an interlocking flap-interface surface which potentially contributes toward flap stability. In addition, the FEMTO LDV Z8 offers flap-position adjustments after docking (before flap-creation). The current study analyzed precision, safety, efficacy, as well as patient self-reported pain and comfort levels after applying two different types of LASIK flap morphologies which were created with a low-energy, high-frequency femtosecond (fs) laser device. A prospective, interventional, randomized, contralateral eye, single-center comparison study was conducted from November 2019 to March 2020 at the Hamburg vision clinic/ zentrumsehstärke, Hamburg, Germany. Eleven patients and 22 eyes received low-energy fs LASIK treatment for myopia or myopic astigmatism in both eyes. Before the treatment, the eyes were randomized (one eye was treated with the 2D, the other eye with the 3D method). The mean central flap thickness one month after surgery was 110.7 1.6 μm (2D) and 111.2 1.7 μm (3D); P = 0.365 (2D vs 3D). Flap thickness measured at 13 different points resulted in no statistically significant differences between any of the measurement points within/between both groups; demonstrating good planarity of the flap was achieved using both methods. Despite not being statistically significant, the surgeons recognized an increase in the presence of an opaque bubble layer in the 3D flap eyes during surgery and some patients reported higher, yet not statistically significant, pain scores in the 3D flap eyes during the first hours after the treatment. Overall, safety- and efficacy indices were 1.03 and 1.03, respectively. In this prospective, randomized, contralateral eye study, the low-energy fs laser yielded predictable lamellar flap thicknesses and geometry at one-month follow-up. Based on these results, efficacy and safety of the corresponding laser application, that is, 2D vs 3D, are equivalent.

The Accuracy of Flap Thickness and Diameter in LASIK Using a Femtosecond Laser.

To evaluate the resultant thickness of the WaveLight FS200 (Alcon Vision, LLC) created LASIK flap compared to intended thickness at the surgical visit, using the WaveLight EX500 (Alcon Vision, LLC) pachymeter and the resultant flap diameter compared to intended diameter. This single arm, prospective, single surgeon study assessed the accuracy of the intended flap thickness and diameter, after successful bilateral LASIK surgery. The WaveLight FS200 femtosecond laser was used to create all flaps with an intended thickness of 120 μm. Flap thickness was calculated by subtracting the stromal bed thickness after flap lift from the preoperative corneal thickness using the WaveLight EX500 on-board optical pachymeter. Flap diameter was determined using digital analysis. A total of 58 subjects (116 eyes) completed the study. The calculated mean flap thickness was 120.6 ± 9.0 μm (range 102 to 143 μm) using the EX500 pre- and post-flap pachymetry measurements. There was no statistically significant difference between the planned and achieved flap thickness (p > 0.05). The mean difference in flap diameter between planned and actual was 0.02 ± 0.05 mm. Corneal thickness measured by Pentacam at up to 2 months preoperatively versus EX500 just prior to surgery was similar, with EX500 measuring 2 μm less on average than the Pentacam. The results suggest that the WaveLight FS200 laser is reliable for LASIK flap thickness and diameter and accurately created flaps at the intended thickness and the intended diameter.

Three-Year Outcomes of Under-flap Stromal Bed CXL for Early Post-LASIK Ectasia.

To investigate the 36-month clinical outcomes of under-flap stromal bed CXL (ufCXL) and report on its ability to stabilize post-laser in situ keratomileusis (LASIK) ectasia. This case series included 20 eyes with diagnosed early post-LASIK ectasia treated with ufCXL. Inclusion criteria were early, mild post-LASIK ectasia, defined as new-onset postoperative manifest refraction cylinder of 1.50 diopters (D) or less, with new topographic inferior steepening consistent with ectasia, uncorrected distance visual acuity of 20/40 or better, and corrected distance visual acuity of 20/25 or better. The existing LASIK flap was lifted, 0.25% isotonic riboflavin was applied directly to the stromal bed, the flap was repositioned, and 18 mW/cm2 ultraviolet light was applied for 5 minutes to the corneal flap surface. Post-ufCXL ophthalmic data were compared to pre-ufCXL baseline measurements. Visual outcomes were maintained pre-ufCXL to 36 months post-ufCXL, with preserved safety index (P = .6545), efficacy index (P = .4980), spherical equivalent accuracy (P = .1536), defocus equivalent accuracy (P = .1032), central corneal thickness (P = .5196), and corneal irregularity indices at 3 mm (P = .8548) and 5 mm (P = .3399). Refractive astigmatism significantly decreased from 0.83 to 0.55 D pre-ufCXL to post-ufCXL (P = .0439), as did maximum keratometry from 42.40 to 42.00 D pre-ufCXL to post-ufCXL (P = .0420). The ufCXL demarcation line depth was 336 ± 21 µm post-ufCXL, with normal endothelial cell density (2,574 ± 203 cells/mm2). Only 1 of 20 eyes showed evidence of progression of 1.00 D in maximum keratometry. The ufCXL procedure shows promise in stabilizing early post-LASIK ectasia. Visual function, refractive astigmatism, maximum keratometry, and corneal irregularity indices were statistically maintained at 36 months postoperatively. [J Refract Surg. 2022;38(8):511-519.].

Flap Amputation and Mitomycin C Application as a Treatment For Corneal LASIK Flap Melting

Flap Amputation and Mitomycin C Application as a Treatment For Corneal LASIK Flap Melting

Are fenestrations in peripheral pre-Descemet’s layer the route for intracameral air bubble migration during femtosecond LASIK?

Femtosecond laser assisted in situ keratomileusis (FS-LASIK) is associated with the creation of cavitation gas bubbles in the stromal dissection plane. Intraoperative intracameral migration of these air bubbles is a rare complication observed during the procedure. At present, it is postulated that the air bubbles created during the photodisruptive process migrate into the anterior chamber via the Schlemm’s canal and trabecular meshwork. This theory; however, does not explain the extremely rare occurrence of this complication. Recently, the pre-Descemet’s layer (PDL) and the presence of fenestrations in its periphery have been described in literature. We present an alternative pathomechanism for intracameral air bubble migration during FS-LASIK based on the anatomical relationship of fenestrations in the peripheral PDL and the termination of Descemet membrane. We propose that the air bubbles migrate directly from the laser dissection plane into the anterior chamber via the fenestrations in the peripheral PDL in cases where the Descemet membrane terminates proximal to the fenestrations. The anatomical variability in the termination of the Descemet membrane in relation to the fenestrations in the peripheral PDL may explain why the complication is not observed in a significant proportion of cases where the LASIK flap border lies in close proximity to the limbus.

Epithelial ingrowth after lasik flap dehiscence during vitreoretinal surgery

Epithelial ingrowth after lasik flap dehiscence during vitreoretinal surgery

Clinical Pearls in Postoperative LASIK Management

More than 35 million LASIK procedures have been performed worldwide with reported improvement in outcomes and safety.1 With proper preoperative screening and advanced technology, visual outcomes are excellent with a low complication rate. This paper reviews potential LASIK complications and treatment options. The majority of complications are minor and resolve with treatment without any adverse effects on visual acuity or quality of vision. Over the past 30 years, there have been significant advances in excimer laser technology, which include improved nomograms, flying spot lasers to deliver smoother ablations, accurate trackers, larger optical zones, aspheric curves, and customized treatments that reduce not only refractive errors but other optical aberrations of the eye. In North America, femtosecond lasers for creation of the corneal flap have generally replaced mechanical microkeratomes that require a blade. Advances in femtosecond technology have shown predictable flap thickness and the ability to customize the diameter, location, hinge, and edge profile of the LASIK flap. CE Notification: This article is available as a COPE accredited CE course. You may take this course for 1-hour credit. Read the article and take the qualifying test to earn your credit. Click here to Enroll (https://www.crojournal.com/clinical-pearls-in-postoperative-lasik-management)

Intraoperative optical coherence tomography-guided management of post-laser-assisted in situ keratomileusis epithelial ingrowth.

We describe a modified technique of intraoperative optical coherence tomography (iOCT)-guided removal of post-laser-assisted in situ keratomileusis (LASIK) epithelial ingrowth with interface ethyl alcohol and mitomycin C application to prevent a recurrence. Epithelial ingrowth was visualized as hyperreflective deposits in the interface on iOCT, and the location and extent were noted at the beginning of the procedure. A simple dimple-down maneuver was performed to help identify the circumference of the LASIK flap. iOCT helped to delineate the flap edge and ensure dissection in the correct plane with complete removal of epithelial cell nests. Real-time visualization of the interface helped in on-table decision making regarding the extent of lifting the flap to encompass the entire region of hyperreflective epithelial ingrowth, as well as the need for additional interventions to ensure complete flap apposition at the end of surgery. All patients gained an uncorrected visual acuity of 20/20–20/25 with no recurrence.

Evolution of corneal thickness and optical density after laser in situ keratomileusis versus small incision lenticule extraction for myopia correction

PurposeTo compare the thickness and stromal optical density (OD) evolution of the flap and cap after femtosecond (FS-LASIK; Visumax) and small incision lenticule extraction (SMILE), respectively, for myopia correction.MethodsA prospective...

The structural and functional corneal reinnervation mechanism at different regions after LASIK-an in vivo confocal microscopy study.

To determine the recovery of structural and functional corneal sensory nerves within the LASIK flap in order to provide insight to more proximal corneal reinnervation and symptoms post-LASIK. Twenty participants underwent femtosecond LASIK with a superior flap hinge. Ocular Comfort Index in Chinese (OCI-C), Cochet-Bonnet esthesiometry, and in vivo confocal microscopy were conducted before surgery and 1week, 1-, 3-, and 6-months post-LASIK to measure symptoms, corneal sensitivity, nerve fiberdensity, width, and the numberofinterconnections within the flap (central and mid-temporal regions), and next to the superior flap hinge. Linear mixed models were used to compare differences between corneal regions at each time point post-LASIK and changes over time post-LASIK. Spearman's correlation tests were used to examine the associations between variables post-LASIK. The least reduction in sensitivity (P < 0.03) and in nerve fiber density (P < 0.02) was found near the flap hinge compared to other regions, but no regional differences were found in nerve fiber width and interconnections. Nerve fiberdensity and the number of interconnections at all regions within the flap recovered over time (P < 0.02). The recovery of corneal sensitivity and nerve fiber width was only seen at the central and temporal regions (P < 0.04). No association was found between sensitivity and nerve parameters, but a higher OCI-C score was associated with a lower nerve fiber density near the hinge (r = - 0.43, P = 0.003) over time post-LASIK. Corneal sensitivity and density are preserved in the hinge, but this preservation of the corneal nerve damage does not affect the nerve morphology.

Corneal stromal roughness after VisuMax and Intralase femtosecond laser photodisruption: An atomic force microscopy study.

PurposeTo compare the induced corneal stromal bed roughness measured with atomic force microscopy (AFM) after LASIK flap creation with the IntraLase 60 kHz and the VisuMax femtosecond laser platforms.MethodsThree freshly enucleated porcine eyes were operated with each femtosecond laser in this experimental study. Standard LASIK treatment parameters were used for the experiment. After LASIK flap creation, the corneal stromal roughness was assessed using a JPK NanoWizard II® AFM in contact mode immersed in liquid. Olympus OMCL-RC800PSA commercial silicon nitride cantilever tips were used. Surface measurements were made in 10 regions of the central cornea of each sample measuring 20 x 20 microns, at 512 x 512 point resolution. Roughness was measured using the root-mean-square (RMS) value within the given regions.ResultsMeasurements from 30 regions of the 3 eyes (10 measurements per eye) in the Intralase (FS1) group, and 30 regions of the 3 eyes (10 measurements per eye) in the VisuMax (FS2) group were analyzed. There was a statistically significant difference in mean ± standard deviation RMS values between the FS1 and the FS2 groups (360 ± 120 versus 230 ± 100 nm respectively; P< 0.00001).ConclusionThis AFM study indicates that the surface of the stromal bed after LASIK flap creation is smoother in the FS2 group than the FS1 group.

Biomechanical Changes to the Cornea from LASIK Flap Creation Resulting in Inaccurate Ablations and Suboptimal Refractive Outcomes with Topographic-Guided Ablation.

PurposeThis study documents a biomechanical corneal change related to corneal flap creation in certain patients leading to an irregular ablation pattern and an inaccurate refractive outcome.MethodsThis retrospective study included consecutive eyes treated with primary LASIK Contoura using the LYRA Protocol. All LASIK procedures were performed on the WaveLight EX500 excimer laser. Flaps were created with either the Alcon WaveLight FS200 femtosecond laser or the Moria M2 microkeratome. Eyes that were off by greater than or equal to 0.50 diopters (D) sphere or cylinder from the targeted goal within 3 months after surgery were identified. Topographical, higher order aberration, and epithelial maps were created. Of these eyes, approximately 10% of eyes were found to have undergone a biomechanical change upon flap creation that led to an inaccurate outcome.ResultsSix representative cases are presented that demonstrate the biomechanical change, outcomes, and treatment. All patients demonstrated an elliptical, irregular ablation pattern on post-operative topography, lateralized the thinnest point of the cornea relative to the corneal apex on Pentacam pachymetry maps, and irregular corneal epithelial thickening at the periphery of the elliptical ablation.ConclusionA biomechanical change during flap creation can occur in certain types of corneas during LASIK flap creation and subsequent treatment with topographic-guided ablation leading to an irregular ablation and suboptimal refractive outcomes.

Quantitative shadowgraphy of aerosol and droplet creation during oscillatory motion of the microkeratome amid COVID-19 and other infectious diseases.

To quantify the atomization of liquid over the cornea during flap creation using microkeratome using high-speed shadowgraphy. Laboratory study. Laboratory investigational study. In an experimental setup, flap creation was performed on enucleated goat's eyes (n = 8) mounted on a stand using One Use-Plus SBK Moria microkeratome (Moria SA) to assess the spread of aerosols and droplets using high-speed shadowgraphy. Two conditions were computed. A constant airflow assumed uniform air velocity throughout the room. A decaying jet assumed that local air velocity at the site of measurements was smaller than the exit velocity from the air duct. With the advancement of the microkeratome across the wet corneal surface, the atomization of a balanced salt solution was recorded on shadowgraphy. The minimum droplet size was ∼90 μm. The maximum distance traversed was ∼1.8 m and ∼1.3 m assuming a constant airflow (setting of refractive surgery theater) and decaying jet condition (setting of an operating theater with air-handling unit), respectively. The microkeratome-assisted LASIK flap creation seemed to cause spread of droplets. The droplet diameters and velocities did not permit the formation of aerosols. Therefore, the risk of transmission of the virus to the surgeon and surgical personnel due to the microkeratome procedure seemed to be low.

Effects of the LASIK flap thickness on corneal biomechanical behavior: a finite element analysis

BackgroundIt is well known that the biomechanical properties change after LASIK refractive surgery. One reason is the impact of flap creation on the residual stroma. The results have revealed that the change is closely related with the flap thickness in several studies. However, the quantitative relationships between the distributions of displacement and stress on the corneal surface and flap thickness have not been studied. The aim of the study was to quantify evaluate the biomechanical change caused by the LASIK flap.MethodsBy building a finite element model of the cornea, the displacement, the stress and the strain on the corneal surface were analyzed.ResultsThe results showed that the corneal flap could obviously cause the deformation of the anterior corneal surface. For example, the displacement of the corneal vertex achieved 15 μm more than that without corneal flap, when the thickness of corneal flap was 120 μm thick. This displacement was enough to cause the change of aberrations in the human eyes. In the central part of the cornea, the stress on the anterior corneal surface increased with flap thickness. But the change in the stress on the posterior corneal surface was significantly less than that on the anterior surface. In addition, the stress in the central part of the anterior corneal surface increased significantly as the intra-ocular pressure (IOP) increase. Furthermore the increase of IOP had a clearly less effect on stress distribution at the edge of the cornea. Distributions of strain on the corneal surface were similar to those of stress.ConclusionsThe changes in the biomechanical properties of cornea after refractive surgery should not be ignored.