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Schnittqualität eines neuen Femtosekundenlasers
Abstract
OBJECTIVE: The aim of this study was to evaluate the cut quality and the cellular damage when using a new 200 kHz femtosecond laser. METHODS: 20 porcine eyes and 3 human eyes, not suitable for transplantation, were used for this study. The WaveLight UltraFlap femtosecond laser was used for flap creation. The surface of the cornea, the structure and ultrastructure of the corneal cells and stroma were evaluated thoroughly using light microscopy (HE-, PAS- and Picrosirius red staining), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). RESULTS: In all eyes, the flap could be lifted very easily and the flap appeared very smooth. Structural and ultrastructural evaluation with light and transmission electron microscopy on epithelium and endothelium showed no side effects of the laser application. The area around the flap cut was minimally affected and the keratocytes and collagen fibres showed minimal alteration due to laser treatment. Scanning electron microscopy revealed in all cases smooth surfaces and precise sidecuts. CONCLUSIONS: Precise corneal flaps can easily be created with this new femtosecond laser. At the same time, no structural and thermal side effects on corneal epithelium, stroma and endothelium appeared. Hence with this new femtosecond laser corneal flaps could be created easily without noteworthy side effects.
... In newer platforms, suction times may be slightly shorter: Salomão et al. reported it was 56 s for the 30 kHz platform, and 40 s for the 60 kHz laser [15]. The introduction of high repetition rate femtosecond lasers has decreased the time needed for flap creation [1,8,71]. The surgeon-related factor might be considered higher in MMK surgeries, and the complications of femtosecond laser flap creation could be less severe and easier to manage. ...
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.
... Previously, Winkler von Mohrenfels et al. 17 evaluated the Wavelight FS200 femtosecond laser in a laboratory setting in 20 porcine and 3 human cadaver eyes. Light microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to assess the surface of the cornea and the structure and ultrastructure of the corneal cells and stroma. ...
Purpose:
To compare the intended versus the resultant thickness of laser in situ keratomileusis (LASIK) flaps created with a new femtosecond laser and to report the 3-month postoperative refractive outcomes.
Setting:
Wellington Eye Clinic, Dublin, Ireland.
Design:
Retrospective consecutive case series.
Methods:
A consecutive series of eyes having LASIK flaps created using a Wavelight FS200 femtosecond laser were included in this analysis. Eyes with preoperative spherical equivalent (SE) myopic refractive errors up to -12.00 diopters (D), hyperopic refractive errors up to +5.50 D, and astigmatism up to 6.00 D received primary LASIK. Outcomes included postoperative flap thickness and 3-month postoperative refraction.
Results:
Outcomes in 431 eyes of 258 patients having LASIK with femtosecond flap creation were assessed. With an intended flap thickness of 120 μm, the mean post-LASIK flap thickness was 120.23 μm ± 13.94 (SD). In 349 of 813 eyes, EX500 optical pachymetry measurements were compared with Scheimpflug pachymetry readings. The mean corneal thickness was 553.52 ± 29.81 μm with optical pachymetry and 553.39 ± 29.12 μm with the Pentacam rotating Scheimpflug camera. In 162 eyes, the flap thickness was measured with optical coherence tomography; the mean was 121.94 ± 10.52 μm. Achieved flap dimensions were as intended.
Conclusions:
This study provides evidence of the predictability and lower variability of LASIK flaps created using the femtosecond laser. Consecutive patients having LASIK had good, predictable, and stable outcomes at the 3-month mark.
To compare stromal bed smoothness in LASIK flaps created with two different femtosecond lasers (IntraLase FS150 and WaveLight FS200) and a mechanical microkeratome (MMK) (Carriazo-Pendular microkeratome).
Sixty freshly enucleated porcine eyes were used for the study. Twenty flaps were created and constitute each of the following three groups: IntraLase FS150 (IFS group), WaveLight FS200 (WFS group) and MMK (MMK group). In each of the three groups, 10 flaps were created with intended thickness of 110 μm and another 10 flaps with 130 μm. Images were assessed with light microscopy and scanning electron microscopy. Qualitative surface roughness grading of the images was performed by five masked observers and statistical comparisons of scores were made between groups.
The results of qualitative surface roughness grading demonstrated that there was no significant difference between the two femtosecond (FS) lasers when comparing the subgroups with the same flap thickness (p>0.05 in both comparisons, Mann-Whitney U test). In addition, there was no statistically significant difference (p>0.05) in each flap maker group between different thickness subgroups. However, the scores of the FS laser subgroups were significantly better than the scores of the MMK subgroups with corresponding flap thicknesses (p<0.05, Mann-Whitney U test).
Our study demonstrates that the IntraLase FS150 and the WaveLight FS200 had a similar performance and provided flaps with smooth surfaces. In comparison to the MMK, the studied femtosecond laser systems had a superior performance in terms of smoothness.
The strongly localized interaction process of ultrashort laser pulses with tissue makes femtosecond lasers a powerful tool for eye surgery. These lasers are now routinely used in refractive surgery and other forms of surgery of the anterior segment of the eye. Several clinical laser systems also offer options for corneal grafting and the potential use of ultrashort pulse lasers in glaucoma surgery has been the object of several recent studies which have shown promising results. While devices aimed for interventions in clear tissue may be based on available solid state or fibre laser technology, the development of tools for surgery in more strongly scattering tissue has to account for the compromised tissular transparency and requires the development of optimized laser sources. The present paper focuses on surgery of clear and pathological cornea as well as sclera. It aims to give an overview over typical medical indications for ultrashort pulse laser surgery, the optics of the tissues involved, the available laser technology, the laser–tissue interaction process, and possible future developments.
The aim of this study was to perform the first femtosecond laser cuts with a new prototype femtosecond laser, in vivo and to evaluate its safety, stability and efficacy.
A LASIK cut was performed with a prototype 200 kHz femtosecond laser in both eyes of nine patients and one eye of two patients (20 individual eyes in total). A complete ophthalmic examination was performed preoperatively and postoperatively at 1, 3, 6 and 12 months after the procedure.
In the pilot series of 20 eyes, flap creation was possible in each case. The mean preoperative manifest refractive spherical equivalent was À-4.22 D (SD ± 61.22 D). The postoperative spherical equivalent refraction was À-0.1 D (SD ± 60.26 D) at 1 month, À-0.22 D (SD ± 60.24 D) at 3 months and À-0.15 D (SD ± 60.16 D) 12 months after surgery.
Femto-LASIK with this new laser system showed high levels of safety, stability and efficacy without any enhancement.
http://www.dimdi.de. DE/CA126/AP4/3332/27/09. Bfam registration 09/03/2009, DE/CA126.
To determine the surface characteristics of human corneal lenticules after femtosecond laser surgery for myopia.
The Carl Zeiss Meditec AG VisuMax® femtosecond laser system was used for refractive correction called Femtosecond Lenticule Extraction on 24 myopic eyes. The surface regularity on the refractive corneal lenticules recovered was evaluated by assessing scanning electron microscopy images using an established scoring system. Three different energy levels 150, 180, and 195 nJ were compared (n = 8 in each group).
Surface irregularities were caused by tissue bridges, cavitation bubbles, or scratches. The surface regularity index (R(2) = 0.74) decreased as pulse energy increased. The average surface regularity score obtained was 7.5 for 150 nJ, 7.25 for 180 nJ, and 6.25 for 195 nJ.
The human corneal lenticules created with the VisuMax® femtosecond laser system are of predictable, good-quality surface. This study shows the influence of pulse energy on surface regularity in human eyes. Further studies should focus on optimization of laser parameters as well as surgical technique to improve the regularity of the corneal stromal bed and so make the advantages of the femtosecond laser technology over conventional techniques clearer in the future.
Recently, laser systems have become available which generate ultrashort laser pulses with a duration of 100-200 femtoseconds (fs). By generating micro-plasmas inside the corneal stroma with fs pulses, it is possible to achieve a cutting effect inside the tissue while leaving the anterior layers intact. The energy threshold to generate a micro-plasma with fs pulses is some orders of magnitude lower than it is for picosecond or nanosecond pulses. This results in a strong reduction of the thermal and mechanical damage of the surrounding tissue.
With a titanium:sapphire fs laser system, the cutting effect on corneal tissue from freshly enucleated porcine eye globes was investigated with different pulse energies. The irradiated samples were examined by light and electron microscopy. The laser-induced pressure transients and the laser-induced bubble formation were analysed with a broadband acoustic transducer and by flash photography.
With fs laser pulses, the extent of thermal and mechanical damage of the adjacent tissue is in the order of 1 microm or below and therefore comparable with the tissue alterations after ArF excimer laser ablation. Using pulse energies of approximately 1-2 microJ and a spot diameter of 5-10 microm, intrastromal cuts can be performed very precisely in order to prepare corneal flaps and lenticules.
Femtosecond photodisruption has the potential to become an attractive tool for intrastromal refractive surgery.
Sirius Red, a strong anionic dye, stains collagen by reacting, via its sulphonic acid groups, with basic groups present in the collagen molecule. The elongated dye molecules are attached to the collagen fibre in such a way that their long axes are parallel. This parallel relationship between dye and collagen results in an enhanced birefringency.
Examination of tissue sections from 15 species of vertebrates suggests that staining with Sirius Red, when combined with enhancement of birefringency, may be considered specific for collagen. An improved and modified method of staining with Sirius Red is presented.
Flap complications using first-generation microkeratomes, such as the Automated Corneal Shaper, were reported in 2.5% (27 of 1,062 eyes). With modern microkeratomes, such as the Hansatome, keratotomy-related complications dropped to 0.16% (46 of 28,201 eyes). Postoperative flap complications, such as flap slippage, occurred in 1.42% (21 of 1,418 eyes), most of them during the first hour after surgery. Interface complications are a new diagnostic entity as the interface between flap and stroma presents an empty space where fluid or cells can accumulate. Diffuse lamellar keratitis usually occurs within the first postoperative days but may also develop later on, triggered, eg, by recurrent corneal erosion. Epithelial ingrowth is a rare complication caused rather by postoperative invasion than by intraoperative implantation, which suggests that the quality of the flap edge and its apposition are very important. Interface fluid is a rare but important phenomenon related to steroid-induced glaucoma but presenting with falsely low tonometry readings.
Femtosecond (fs) laser pulses may offer new possibilities in the field of refractive surgery, especially when using the laser as a microkeratome. By induction of nonlinear absorption processes the laser can be used to perform intrastromal cuts. The conventional microkeratome, associated with numerous potential side effects, can possibly be replaced. Furthermore, refractive lenticules can be prepared within the stroma and removed in a single-step operation.
In 10 rabbits, cuts were made to create both a lamellar flap and an intrastromal refractive lenticule. The flap was lifted, the lenticule was extracted and, finally, the flap was repositioned (intrastromal laser keratomileusis, ILK). The corneal samples were collected up to 120 days after treatment and processed for histopathological analysis.
All flaps could be opened and prepared lenticules could be extracted in one piece by the surgeon. The treated corneas developed a mild wound healing reaction, comparable to that known from excimer laser in situ keratomileusis (LASIK) studies. The wound healing was restricted to the flap-stroma interface, most pronounced at the periphery of the flaps.
The use of the fs-laser offers new possibilities in preparation of corneal flaps, possibly providing advantages over conventional microkeratomes. Furthermore, the fs-laser has the potential to create intrastromal refractive lenticules for complete refractive procedures (ILK).
To determine the flap thickness accuracy of 6 microkeratome models and determine factors that might affect flap thickness.
Magill Research Center for Vision Correction, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.
This multicenter prospective study involved 18 surgeons. Six microkeratomes were evaluated: AMO Amadeus, Bausch & Lomb Hansatome, Moria Carriazo-Barraquer, Moria M2, Nidek MK2000, and Alcon Summit Krumeich-Barraquer. Eyes of 1061 consecutive patients who had laser in situ keratomileusis were included. Age, sex, surgical order (first or second cut), keratometry (flattest, steepest, and mean), white-to-white measurement, laser used, plate thickness, head serial number, blade lot number, and occurrence of epithelial defects were recorded. Intraoperative pachymetry was obtained just before the microkeratome was placed on the eye. Residual bed pachymetry was measured after the microkeratome cut had been created and the flap lifted. The estimated flap thickness was determined by subtraction (ie, mean preoperative pachymetry measurement minus mean residual bed pachymetry).
A total of 1634 eyes were reviewed. Sex distribution was 54.3% women and 45.7% men, and the mean age was 39.4 years +/- 10.6 (SD). In addition, 54.5% of the procedures were in first eyes and 45.5%, in second eyes. The mean preoperative pachymetry measurement was 547 +/- 34 microm. The mean keratometry was 43.6 +/- 1.6 diopters (D) in the flattest axis and 44.6 +/-1.5 D in the steepest axis. The mean white-to-white measurement was 11.7 +/- 0.4 mm. The mean flap thickness created by the devices varied between head designs, and microkeratome heads had significant differences (P<.05). Factors that explained 78.4% of the variability included microkeratome model, plate thickness, mean preoperative pachymetry, Kmin, surgery order, head serial number, blade lot number, and surgeon. Factors such as age, sex, Kmax, Kaverage, white to white, and laser had no significant correlation to flap thickness.
The results demonstrated variability between the 6 microkeratome models. Device labeling did not necessarily represent the mean flap thickness obtained, nor was it uniform or consistent. Thinner corneas were associated with thinner flaps and thicker corneas with thicker flaps. In addition, first cuts were generally associated with thicker flaps when compared to second cuts in bilateral procedures.
To describe the constellation of subjective and objective findings associated with unusual occurrences of photosensitivity after laser in situ keratomileusis (LASIK) with femtosecond flap creation and identify optimal management strategies.
Demographic data, laser settings, subjective complaints, clinical findings, treatment, and response to treatment were recorded for suspected cases of transient postoperative photosensitivity from 3 surgeons operating at 3 different sites. All cases were estimated for the period covering the suspected cases at each site to assess incidence. Additional cases were solicited from IntraLase users via a survey.
For the 3 sites, 63 eyes from 33 patients were reported of a total estimated case log of 5667 (incidence, 1.1%). Average age was 41 years, and 51.7% of patients were women. Onset of symptoms ranged from 2 to 6 weeks after uneventful LASIK. All patients were treated with prednisolone acetate drops, whereas 1 surgeon also used Restasis (cyclosporine ophthalmic solution 0.05%). Patients noted improvement of symptoms within 1 week of treatment. When the raster and side-cut energy settings were lowered (by an average of 24% and 33%, respectively), significant reductions in incidence were noted. Similar findings were reported by 3 additional surgeons reporting 17 cases in the survey of IntraLase users.
This report describes a new complication of LASIK performed with a femtosecond laser keratome that may be related to the pulse energy used for flap creation. Although there is no loss of uncorrected visual acuity, symptoms can be prolonged, especially without prompt steroid therapy. Technical advances that reduced pulse energies appear to decrease the incidence.
To describe the incidence of transient light-sensitivity syndrome (TLSS) after laser in situ keratomileusis (LASIK) with the femtosecond laser and to identify preventive strategies.
Hospital NISA Virgen del Consuelo, Valencia, Spain.
The first 765 eyes operated on with the 15 KHz femtosecond laser were prospectively analyzed for subjective complaints and clinical findings compatible with TLSS. Intraoperative settings, postoperative treatment, and development of complications were analyzed.
Overall, TLSS developed in 10 eyes (incidence 1.3%). However, the incidence decreased from 2.8% to 0.4% when aggressive topical steroids were used during the first 3 postoperative days. Postoperative interface inflammation and postoperative use of a low-dose topical steroid regimen were associated with a higher incidence of TLSS.
Transient light-sensitivity syndrome is a relatively uncommon complication related to the use of the femtosecond laser. Postoperative interface inflammation may increase the probability of developing TLSS, whereas an aggressive postoperative steroid regimen seemed to provide protection against it.