Laser In Situ Keratomileusis Flap Creation Research Articles

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.

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.

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.

Reproducibility of laser in situ keratomileusis flap thickness using a new multifunctional femtosecond laser platform and correlation with clinical preoperative measurements

To analyze the reproducibility of laser insitu keratomileusis (LASIK) flap thickness (target 120μm) using the multifunctional femtosecond laser (Lensx) and correlate postsurgical measurements with preoperative factors. Hospital Oftalmológico Visão Laser, Santos, São Paulo, Brazil. Prospective case series. Patients with stable refraction for over a year were evaluated. Patients who submitted to refractive surgery with -1.25 to -6.00 diopters (D), with or without astigmatism up to -4.00 D, and corneal curvature of 40.00 to 47.00 D were included. At 100days postoperatively, an independent examiner performed 4 high-resolution tomographic sections of the cornea for each eye at 45- to 225-degree, 90- to 270-degree, 135- to 315-degree, and 0- to 180-degree meridians. Two masked experienced observers analyzed each section using measuring points located at the center of the cornea (0.0mm), 2.0mm to the left and to the right of the center, and 4.0mm to the left and to the right of the center. The study comprised 33 patients (63 eyes), aged 21 to 50years. A significant difference from the target flap thickness (120μm) was found in 2 of 20 measurements; however, the actual difference was approximately 2.2μm. Interrater reliability was excellent (ICC>0.75), with an interrater bias close to 0. Clinical measurements were not predictive of the set of 20 postoperative measurements. Reproducibility of the multifunctional femtosecond laser was good for LASIK flap creation and no predictive correlation was found with preoperative clinical factors.

Assessment of Tear Osmolarity and Other Dry Eye Parameters in Post-LASIK Eyes

To assess the tear osmolarity using the TearLab device after laser in situ keratomileusis (LASIK) and to compare the values with those obtained by traditional tear film tests before and after the procedure. Thirty eyes of 15 refractive surgery candidates (5 men and 10 women of mean age: 30.55 ± 11.79 years) were examined. Using a special questionnaire (Ocular Surface Disease Index), subjective dry eye complaints were evaluated, and then, the tear osmolarity was measured with the TearLab system (TearLab Corporation) and conventional dry eye tests were carried out. Examinations were performed preoperatively and at 1, 30, and 60 days after the surgery. The mean value of tear osmolarity was 303.62 ± 12.29 mOsm/L before the surgery and 303.58 ± 20.14 mOsm/L at 60 days after the treatment (P = 0.69). Mean lid parallel conjunctival folds value was 0.68 ± 0.68 before the procedure and 0.58 ± 0.65 subsequent to surgery (P = 0.25). Meibomian gland dysfunction was not detected. No significant deviation was observed in the values of Schirmer test, corneal staining, tear break-up time, and lid parallel conjunctival folds when compared with postoperatively obtained values during the follow-up period (P > 0.05). During LASIK flap creation, intact corneal innervation is damaged, and the ocular surface lacrimal functional unit can be impaired. In our study, no abnormal dry eye test results were observed before or after the procedure. Based on our results, LASIK treatment is safe for dry eye involving the administration of adequate artificial tears for a minimum of 3 months.

Comparison of eye-tracking success in laser in situ keratomileusis after flap creation with 2 femtosecond laser models

To determine the efficiency of an eye tracker after laser in situ keratomileusis (LASIK) flap creation with 1 of 2 femtosecond laser models. Tertiary referral center, Singapore National Eye Center, Singapore. Randomized clinical trial. The LASIK flap was created with an IntraLase (Group A) or a VisuMax (Group B) femtosecond laser. An Advanced Control Eye Tracker was initiated 3 times to obtain iris recognition. Eye tracking was considered successful if the eye movements could be followed despite the presence or absence of an opaque bubble layer (OBL). Univariate-multivariate logistic regression analysis was performed. Preoperatively, the mean values (ranges) of the 87 eyes were sphere, -5.64 diopters (D) ± 2.17 (SD) (-9.75 to -0.25 D); cylinder 1.65 ± 1.63 D (-3.75 to 0.00 D); optical zone, 6.34 ± 0.20 mm (5.6 to 7.0 mm); keratometry, 43.48 ± 1.32 D (40.1 to 42.8 D); flap thickness, 109.30 + 5.21 μm (90 to 115 μm). Eye tracking was successful in 38 (90.5%) of 42 eyes in Group A and 43 (95.6%) of 45 eyes in Group B. No specific type of OBL was seen in either group. The LASIK was completed in all eyes. There was a statistically significant association between positive tracking and a smaller optical zone (P=.03). There were no statistically significant differences in eye tracking between the 2 femtosecond lasers. Eye tracking was achieved in more than 90% of cases after LASIK flap creation with 1 of 2 femtosecond laser models, even in the presence of an OBL.

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

To compute and compare visual acuity, refractive outcomes, and anterior corneal aberration changes after myopic laser in situ keratomileusis (LASIK) with flap creation by a mechanical microkeratome and by a femtosecond laser. Private practice refractive surgery center, Valencia, Spain. Comparative case series. Patients were assigned to have LASIK flap creation with a mechanical microkeratome (Carriazo-Barraquer) or a femtosecond laser (IntraLase). The Visx S2 excimer laser was used for myopic ablation in all cases. Main outcome measures included uncorrected and corrected distance visual acuities and the defocus equivalent. Higher-order aberrations (HOAs) were computed from the anterior corneal surface measured with topography for 4.0 mm and 6.0 mm pupil diameters before and 48 months after surgery. The study evaluated 50 patients (98 eyes). The root mean square of HOAs increased postoperatively by a factor of approximately 1.9 in both groups and with both pupil diameters. There were no statistically significant differences between the 2 groups in the increase in anterior corneal aberrations, mean postoperative visual acuity, or residual refraction. All visual and optical performance metrics remained stable throughout the 4-year follow-up. There were no complications with flap creation and no postoperative complications. The increase in anterior corneal aberrations after myopic LASIK was similar after mechanical microkeratome and femtosecond laser flap creation. Visual acuity, refraction, and the optical quality of the cornea after LASIK remained stable through 4 years postoperatively in both groups.

Macular hemorrhage after laser in situ keratomileusis (LASIK) with femtosecond laser flap creation

To report the first case of macular hemorrhage following laser in situ keratomileusis (LASIK) with femtosecond laser flap creation. Observational case report. A 36-year-old woman underwent uncomplicated, bilateral, simultaneous LASIK procedures for correction of moderate myopia (-5.00 diopters OD and -6.00 diopters OS). LASIK flap creation was performed using the IntraLase femtosecond laser. On postoperative day 1, the patient's uncorrected and best-corrected visual acuities were 20/20 OD and 20/40 OS. A dilated fundoscopic examination revealed a one-third disk diameter macular hemorrhage OS. An intravenous fluorescein angoiogram ruled out the presence of predisposing macular pathology. Two months after LASIK, the macular hemorrhage had cleared, and 6 months later, the BCVA improved to 20/25 OS. Macular hemorrhage may occur after LASIK, even in the absence of previously identified risk factors, such as high myopia, pre-existing choroidal neovasculaization, lacquer cracks, and sudden changes in intraocular pressure associated with microkeratome-assisted flap creation.

Laser In Situ Keratomileusis Flap Stability During Simulated Aircraft Ejection in a Rabbit Model

To determine the stability of the laser in situ keratomileusis (LASIK) flap in a rabbit model when subjected to vertical acceleration at nine times the force of gravity (+9 Gz) in an aircraft cockpit ejection simulator. Thirty-six eyes from 25 New Zealand white rabbits underwent LASIK flap creation without laser photoablation. One month after surgery, the rabbits were sedated and harnessed in a cockpit ejection seat simulator used to train United States Air Force pilots. They then underwent a controlled rapid-sequence ejection at +9 Gz. Subsequently, the rabbits were euthanized and the corneas harvested for microscopic examination. Refractive measurements and corneal examination were made before LASIK flap creation and prior to and after the +9 Gz ejections. Determination of LASIK flap dislocation was based on clinical observation of flap slippage or a significant shift in pre-ejection to postejection cylinder axis. The average preoperative refraction of the rabbit eye was +1.83 D + 3.25 D x 086 degrees. The average change from pre-ejection to postejection was 0.04 D sphere, 0.02 D cylinder, 6.8 axis degrees, and 0.04 D spherical equivalent. The pre-ejection to postejection measurements were not statistically significantly different by a paired test. Laser in situ keratomileusis flap dislocation or ejection-induced corneal folds or striae were not clinically observed. Histologic examination revealed well-healed LASIK flaps but no reactive keratocytes at the central stromal-stromal interface. Healed LASIK flaps as created in this rabbit model without laser ablation are stable when subjected to a rapid vertical ejection at nine times the force of gravity.