Femtosecond Research Articles

Comparison of the Ziemer FEMTO LDV Femtosecond Laser and Moria M2 Mechanical Microkeratome

To assess and compare the dimensions of LASIK flaps created by the Ziemer FEMTO LDV "Classic" femtosecond (FS) laser and Moria M2 microkeratome with 110-μm head and -20 blade. Seven hundred twenty eyes from 360 consecutive patients were enrolled in this study and divided into two groups of equal size for flap creation with the Ziemer LDV (FS laser group) and Moria M2 mechanical microkeratome (microkeratome group). Nominal flap thickness was 110 μm for all patients and for both devices. Flap thickness was measured by Fourier-domain optical coherence tomography in 14 specified positions on each flap 1 week after surgery to analyze the regularity, uniformity, and accuracy of the two types of LASIK flaps. The mean deviation between achieved and attempted flap thickness was smaller in the FS laser group than in the microkeratome group. The flaps in the FS laser group were more regular and uniform, showing an almost planar configuration, whereas flaps in the microkeratome group had a meniscus shape and were significantly thicker near the flap edge. Nasal and temporal flap thickness did not differ significantly in the FS laser group, whereas in the microkeratome group, characteristic differences in temporal versus nasal flap thickness were noticed. Within the 5040 individual measurements of the 360 eyes, deviations of >20 μm were observed in 0.73% of eyes in the FS laser group and 42.4% in the microkeratome group. The dimensions of flaps created by the Ziemer LDV femtosecond laser were more uniform and accurate than those created by the Moria M2 microkeratome.

Intrastromal Corneal Ring Segment Implantation by Femtosecond Laser for the Correction of Residual Astigmatism After Penetrating Keratoplasty

To evaluate the safety and efficacy of intracorneal ring segments (ICRSs) aided by femtosecond (FS) laser for the correction of residual astigmatism after penetrating keratoplasty (PKP). This retrospective noncomparative study comprised 14 eyes of 14 patients with high astigmatism after PKP who had ICRS implantation by femtosecond laser. The study evaluated uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive astigmatism, and corneal maximum curvature. The CDVA postoperatively improved after 3 months (P < 0.001) and 6 months (P < 0.001) compared with CDVA preoperatively. The CDVA at 3 months was similar to that at 6 months (P > 0.999) as well as the UDVA (P = 0.276). The preoperative astigmatism was higher than that after surgery (P = 0.001). The preoperative maximum curvature was higher than that of the postoperative maximum curvature (P < 0.001). The implantation of ICRSs using the femtosecond laser for residual astigmatism post-PKP was safe and showed satisfactory results. It reduced refractive astigmatism and maximum corneal curvature and improved UDVA and CDVA.

Interface quality of endothelial keratoplasty buttons obtained with optimised femtosecond laser settings

AimTo optimise interfaces of endothelial buttons created with femtosecond (FS) lasers.SettingDepartment of Ophthalmology, Hôtel-Dieu Hospital, Paris, France.MethodsForty-two corneas were divided into five groups of various cutting patterns and a control...

Internal Aberrations and Optical Quality After Femtosecond Laser Anterior Capsulotomy in Cataract Surgery

To compare ocular and internal aberrations after femtosecond laser anterior capsulotomy and continuous curvilinear capsulorrhexis in cataract surgery. In this prospective study, anterior capsulotomy was performed during cataract surgery with an intraocular femtosecond (FS) laser (Alcon LenSx Inc) in 48 eyes. As a control group, continuous curvilinear capsulorrhexis (CCC) was performed in 51 eyes. Wavefront aberrometry, corneal topography, and objective visual quality were measured using the OPD-Scan (NIDEK Co Ltd). Vertical and horizontal tilt, coma, and visual quality metrics were evaluated separately to determine whether the source of aberrations was ocular or internal. Main outcome measures included postoperative residual refraction, uncorrected and corrected visual acuities, ocular and internal aberrations, Strehl ratio, and modulation transfer function (MTF). No statistically significant differences were noted between the FS and CCC groups, respectively, in postoperative sphere (-0.60 ± 1.50 vs -0.50 ± 1.40 diopters [D]), postoperative cylinder (1.30 ± 1.01 vs 1.10 ± 1.10 D), uncorrected distance visual acuity (0.86 ± 0.15 vs 0.88 ± 0.08), or corrected distance visual acuity (0.97 ± 0.08 vs 0.97 ± 0.06). The FS group had significantly lower values of intraocular vertical tilt (-0.05 ± 0.36 vs 0.27 ± 0.57) and coma (-0.003 ± 0.11 vs 0.1 ± 0.15), and significantly higher Strehl ratios (0.02 ± 0.02 vs 0.01 ± 0.01) and MTF values at all measured cycles per degree, compared to the CCC group. Capsulotomy performed with an intraocular FS laser induced significantly less internal aberrations measured by the NIDEK OPD-Scan aberrometer compared to eyes that underwent CCC, which may result in better optical quality after the procedure.

Treatment of Corneal Opacity by Planned Lamellar Keratectomy Using the Femtosecond Laser

To report successful vision restoration after lamellar keratectomy using a femtosecond (FS) laser in a patient with superficial corneal opacity that developed after an episode of epidemic keratoconjunctivitis. A 19-year-old girl with corneal opacity in the left eye was referred to our department for treatment. The opacity was principally located within the superficial anterior cornea. To remove the opacity with minimization of change in the keratometric value, we performed lamellar keratectomy with the aim of creating a 100-μm-thick flap, using an FS laser (IntraLase FS; AMO, Irvine, CA). Postoperatively, corneal opacity was removed and vision improved. Six months after surgery, the corneal surface was stable and smooth, and no corneal haze was observed. The keratometric value measured by corneal topography and manifest refraction showed no hyperopic shift postoperatively. This report indicates that the FS laser may be an effective surgical tool for the treatment of patients with corneal opacity and that hyperopic shift is not of concern.

Ex vivo evaluation of femtosecond pulse laser incision of urinary tract tissue in a liquid environment: Implications for endoscopic treatment of benign ureteral strictures

The femtosecond (FS) pulse laser incises soft tissues with minimal peripheral damage and is a promising cutting tool for ureteroscopic endoureterotomy of benign ureteral strictures. To evaluate the feasibility of applying the FS laser to ureteroscopic endoureterotomy. A commercial Ti:Sapphire regenerative amplifier system (Coherent, RegA 9050, USA) was used in this study. Normal saline, 5% glucose solution, 4% mannitol solution, distilled water, and a 1% (v/v) suspension of whole blood with each of these solutions were tested for their attenuation rate (AR) of the FS laser's power. Bladder specimens from Sprague-Dawley (SD) rats were used as a surrogate model. The laser incised slots of 2 mm in length at bladder samples using three power grades (5×, 10×, and 20× the threshold power) combined with five effective pulse rates (40, 20, 10, 5, and 2.5 kHz), both in air and in normal saline. After samples were processed with standard hematoxylin-eosin staining procedures, the incision depth and collateral damage range were determined microscopically. The ARs of blood suspensions with each of the three isosmotic solutions were significantly higher than the other five solutions (P < 0.001). The FS laser's cutting depth and the collateral damage were increased with the laser power or power density but the collateral damages were less than 100 µm. Microbubble formation was detected in the liquid environments tested and influenced the effective laser power. Endoscopic application of the FS laser is feasible. Microbubble formation with the laser incision, however, may influence cutting effects. Proposed methods to address these issues include increasing the irrigation rate, using distilled water as irrigation or using gas insufflation instead of irrigation. It is necessary to evaluate these methods, as well as the long-term biologic response to laser incision, on living animal models in endoscopic settings before use on humans.

Superelasticity and the propagation of shock waves in crystals

The invention of lasers capable of generating fem� tosecond pulses opens a way for investigating fast pro� cesses in matter. The development of the diagnostic methods for the subpicosecond timescale was of exceptional importance. With these methods, not only the generation, but also the measurement of fast pro� cesses initiated by a femtosecond laser became possi� ble. The initiation and measurements are performed with a pair of ultrashort pulses using the stroboscope principle [1–7]. The first pulse in the pair is a high� power pump pulse and the second pulse is a weak probe pulse (pump–probe method). Both pulses are formed by means of the separation of a single initial pulse. They pass through paths with different optical lengths and arrive at a target at different times. The time delay t delay of the arrival of the probe pulse with respect to the pump pulse is varied by the controlled variation of the optical length. Thus, a series of the phases and amplitudes of the probe pulse reflected from the place of the action of the pump pulse in t delay is obtained. The phases and amplitudes provide infor� mation on time variation of the optical characteristics and on the fast evolution of heated matter. The pump pulses and the places of the irradiation of the target should be the same in different experiments of the series for success of the pump–probe method.

Nanostructured thin film formation on femtosecond laser-textured Ti–35Nb–xZr alloy for biomedical applications

The aim of this study was to investigate the nanostructured thin film formation on femtosecond (FS) laser-textured Ti–35Nb–xZr alloy for biomedical applications. The initial surface roughening treatment involved irradiation with the FS laser in ambient air. After FS laser texturing, nanotubes were formed on the alloy surface using a potentiostat and a 1 M H 3PO 4 solution containing 0.8 wt.% NaF with an applied cell voltage of 10 V for 2 h. The surface phenomena were investigated by FE-SEM, EDS, XRD, XPS and a cell proliferation test. It was found that nanostructured Ti–35Nb–xZr alloys after FS laser texturing had a hybrid surface topography with micro and nano scale structures, which should provide very effective osseointegration.

Alternative Applications of the Femtosecond Laser in Ophthalmology

Purpose: To provide an update of novel applications for the femtosecond (FS) laser in ophthalmology. Design: Perspective, literature review, case report, and commentary. Methods: Literature review. Results: The many advantages of etching flaps with the FS laser for laser in situ keratomileusis (LASIK) have been well established. Alternative applications of the FS have been approved and are now used in clinical practice. In refractive ophthalmology, the FS laser can be used for lenticule extraction to correct myopia and intrastromal biochemical manipulation to correct presbyopia. This laser can be used for preparing host and donor tissue for both full thickness and lamellar keratoplasty. Research is underway, exploring ways to employ the FS laser for different stages of cataract surgery. Cosmetic procedures with FS-assisted tattooing serve to correct leukoria. Conclusions: Advancements in technology have allowed measurable improvements in the surgical safety, efficiency, speed, and versatility of FS lasers in ophthalmology.

Micropatterning and characterization of electrospun poly(ε‐caprolactone)/gelatin nanofiber tissue scaffolds by femtosecond laser ablation for tissue engineering applications

Experimental investigations aimed at assessing the effectiveness of femtosecond (FS) laser ablation for creating microscale features on electrospun poly(ε-caprolactone) (PCL)/gelatin nanofiber tissue scaffold capable of controlling cell distribution are described. Statistical comparisons of the fiber diameter and surface porosity on laser-machined and as-spun surface were made and results showed that laser ablation did not change the fiber surface morphology. The minimum feature size that could be created on electrospun nanofiber surfaces by direct-write ablation was measured over a range of laser pulse energies. The minimum feature size that could be created was limited only by the pore size of the scaffold surface. The chemical states of PCL/gelatin nanofiber surfaces were measured before and after FS laser machining by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) and showed that laser machining produced no changes in the chemistry of the surface. In vitro, mouse embryonic stem cells (mES cells) were cultured on as-spun surfaces and in laser-machined microwells. Cell densities were found to be statistically indistinguishable after 1 and 2 days of growth. Additionally, confocal microscope imaging confirmed that spreading of mES cells cultured within laser-machined microwells was constrained by the cavity walls, the expected and desired function of these cavities. The geometric constraint caused statistically significant smaller density of cells in microwells after 3 days of growth. It was concluded that FS laser ablation is an effective process for microscale structuring of these electrospun nanofiber tissue scaffold surfaces.

A Novel Technique: Eccentric Lamellar Keratolimbal Allografting Using a Femtosecond Laser

To report on a patient who received an eccentrically designed lamellar keratolimbal allograft prepared using a femtosecond (FS) laser to preserve peripheral curvature. A 19-year-old woman, with a pseudopterygium on the left eye resulting from dermoid excision about 11 years earlier, received an eccentric lamellar keratolimbal allograft in a procedure involving FS laser use. Corneal flaps of depths 280 and 400 mum and diameters 6.5 and 6.6 mm were eccentrically created by FS laser treatment of the recipient and donor eyes, respectively, after removal of the pseudopterygium. After amniotic membrane transplantation, the eccentrically designed corneal flap was secured with 10-0 nylon sutures. Corneal flap creation was uneventful. Only minimal suturing was required for lamellar keratoplasty, and no complications occurred. Twelve months after surgery, a stable corneal surface was observed, with minimal scar formation at the graft margin and relatively good graft interface clarity. Eccentric lamellar keratolimbal allografting using an FS laser is an effective and time-saving surgical method to treat peripheral corneal abnormalities featuring corneal opacity.

A New Surgical Technique: A Femtosecond Laser-Assisted Keratolimbal Allograft Procedure

To evaluate the feasibility of a femtosecond (FS) laser-assisted keratolimbal allograft (KLAL) technique. Interventional case series. This study included 3 patients with extensive limbal stem cell deficiency. The donor cornea was dissected with an FS laser (IntraLase FS laser, 60 kHz) using a ring procedure, without outer side cutting for the limbal graft, after a penetrated dissection of the donor cornea prior to penetrating keratoplasty (PKP). The depth and width of the ring procedure were adjusted for each individual patient. Further extension to the periphery of the sclerocorneal tissue of the donor graft was performed with a diamond knife. In a case of KLAL alone, the unhealthy limbal tissue of the recipient was removed with the FS laser by the same method employed in donor preparation. One patient underwent KLAL alone, and 2 patients underwent KLAL combined with PKP. The patients were followed up for a maximum of 10 months. Limbal grafts were even and thin, as expected. The case with KLAL alone showed the fastest epithelization of the recipient cornea. The 2 cases of combined KLAL and PKP showed excellent approximation between recipient and donor tissue. The ocular surfaces have been stable for 8 months in case 1 and 10 months in cases 2 and 3. FS laser-assisted KLAL has potential advantages in terms of simplicity and speed as compared with conventional techniques.

The Comparison of Femtosecond Laser-Assisted Penetrating Keratoplasty With Conventional Surgery in Terms of Endothelial Safety: Ex Vivo Study Using Porcine Eyes

To evaluate the effect of using femtosecond (FS) laser technology for penetrating keratoplasty (PK) in terms of corneal graft endothelial ultrastructure and viability in porcine eyes. Thirty-two freshly enucleated porcine eyes were divided into 4 equal groups (n = 8): group 1, incomplete penetration using the FS laser (a 100 microm-depth from the endothelial side remained); group 2, complete penetration using the FS; group 3, trephination using a vacuum trephine until the aqueous humor appeared; group 4, no treatment (control group). For groups 1 and 2, side cuts were performed using a 60-kHz FS laser (IntraLase FS Laser, Abbot Medical Optics, Abbott Park, IL). Preoperative ultrasound pachymetry was used to make measurements at 5 positions. Scanning electron microscopy (SEM) was used to determine morphological changes, and light microscopy with Alizarin red staining was used to determine the amount of cell death. Preoperative corneal thicknesses were similar for all groups. All 4 groups showed similar corneal endothelial cell morphology and viability at the graft center (P = 0.15, Kruskal-Wallis test). At the graft border, endothelial cell damage was minor in group 1, moderate in group 2, and most severe and diffuse in group 3 (P = 0.009, Kruskal-Wallis test). FS laser use is safe for the endothelium at the graft center and has less harmful effects on the endothelium at the incision area than does conventional trephination. Therefore, FS laser-assisted corneal grafts with complete penetration seems to be the optimum choice for preserving endothelial cells during PK.

New Surgical Strategy for Corneal Tattooing Using a Femtosecond Laser

The purpose of this study was to describe a new method of femtosecond (FS) laser-assisted corneal tattooing and to report the results of this method in a case series. The study involved 6 eyes of 6 patients with total or partial corneal opacity. An FS laser was used for lamellar dissection and to make a side cut with a hinge, creating a corneal flap. Laser parameters were adjusted depending on ocular condition and the location of the corneal opacity. After lifting the corneal flap, further lamellar dissection with a diamond blade was performed up to the periphery of the limbal area. Using a cannula, dye was injected into the lamellar stromal bed and the space of the lamellar dissected pocket in the limbus, after which the flap was repositioned. The design and application of the FS laser for dissection and flap creation were successful in all cases. There were no significant complications other than an incomplete cut under band keratopathy in 1 eye. The cosmetic effects were satisfactory in all cases. No patient complained of pain for more than 1 day after surgery. The advantages of the FS laser-assisted corneal tattooing include a customized design, speed, decreased pain, reduced risk of perforation, and good wound healing. This procedure provides improvements over current corneal tattooing techniques, although it is relatively expensive.

Femtosecond Lasers in Ophthalmology

To provide an update and review of femtosecond (FS) lasers in clinical ophthalmology. Perspective, literature review, and commentary. Selected articles from the literature and the authors' clinical and laboratory studies. The FS laser employs near-infrared pulses to cut tissue with minimal collateral tissue damage. Although its major use at present is in the cutting of laser in situ keratomileusis flaps, the laser has proven its versatility in laser-assisted anterior and posterior lamellar keratoplasty, cutting of donor buttons in endothelial keratoplasty, customized trephination in penetrating keratoplasty, tunnel creation for intracorneal ring segments, astigmatic keratotomy, and corneal biopsy. Current laboratory studies include all-FS laser refractive keratomileusis sans flap, cutting corneal pockets for insertion of biopolymer keratoprostheses, noninvasive transscleral glaucoma surgery, retinal imaging and photodisruption, presbyopia surgery, and anterior lens capsulorrhexis. Advances in ultra-fast laser technology continue to improve the surgical safety, efficiency, speed, and versatility of FS lasers in ophthalmology.

Corneal Endothelial Viability After Femtosecond Laser Preparation of Posterior Lamellar Discs for Descemet-Stripping Endothelial Keratoplasty

To evaluate the feasibility of the femtosecond (FS) laser in preparation of posterior lamellar discs (PLDs) and to study the effect on endothelial cell (EC) viability for Descemet-stripping endothelial keratoplasty. Fourteen human donor bulbi unsuitable for transplantation were used. A horizontal lamellar cut was prepared in the donor cornea with an FS laser by using a raster and/or a spiral spot pattern. The control group consisted of the paired cornea of the same donor. EC density was evaluated before and after preservation in organ culture. The PLD was stripped from the anterior part by using either a forceps or a blunt dissection technique. The damage to the endothelium was evaluated. EC loss after organ storage was not statistically significant between the FS cornea group and the control group in the 15- (7.7% +/- 6.9% and 8.9% +/- 8.1%, respectively; P = 0.78) and 30-kHz (4.3% +/- 4.0% and 3.7% +/- 3.6%, respectively; P = 0.75) group. There was no significant effect of laser frequency (15 vs. 30 kHz) on EC loss (7.7% vs. 4.3%, P = 0.25). Dissection by using a forceps stripping technique resulted in higher EC loss than that with a blunt dissection technique (13.0% vs. 6.5%, P = 0.03). EC loss after FS laser lamellar cutting is not dependent on the frequency (ie, energy level) of the laser. A blunt dissection technique of PLDs resulted in acceptable EC loss and supports the clinical use of the FS laser for the preparation of PLDs.

The role of the Femtosecond (FS) laser in lamellar keratoplasty

Abstract Purpose: To evaluate the safety and feasibility of the FS laser for the preparation of posterior lamellar discs and to evaluate the first clinical results of a new technique – Femtosecond Laser Descemet Stripping Endothelial Keratoplasty (FS‐DSEK) – for surgical treatment of corneal diseases.Setting: Department of Ophthalmology, Academic Hospital, Maastricht, The Netherlands. Cornea Bank, Amsterdam, The Netherlands. University Medical Center, Groningen, The Netherlands. University Medical Center St. Radboud, Nijmegen, The Netherlands, Eye Hospital Rotterdam. Methods: A 30 kHz FS laser (IntraLase Corp., Irvine, CA) was used to prepare a lamellar cut in the cornea of human donor eyes. After FS laser preparation of a 9.5 mm wide lamellar cut at a depth of 400 micron, the corneoscleral button was stored in organ culture medium. The endothelial viability was assessed after preparation of the lamellar cut and after dissection of the donor posterior lamellar disc (PLD) from the anterior cornea. In ten eyes of ten patients with pseudophakic bullous keratopathy the PLDs were used for endothelial keratoplasty. The follow‐up ranged from 13 to 26 weeks. Results: The mean±sd endothelial cell loss after FS preparation of the lamellar cut (n=4) was 3.4%±3.5% and after dissection of the posterior lamellar disc (n=5) was 6.5%±3.2%. There was no significant difference in endothelial cell loss between FS and non‐FS laser treated corneas after organ culture (p=0.46).All eyes had a clear graft with functioning endothelium. In 4 eyes BCVA was 20/40 to 20/50. In the other 6 eyes BCVA ranged from 20/200 to 20/40 and 5/6 eyes had pre‐existing maculopathy. The surgically induced astigmatism was 2.1 D. Longer‐term results will be presented to assess graft clarity and visual outcomes in the other eyes. Conclusions: FS laser preparation of posterior lamellar discs is safe and feasible for performing FS‐DSEK. We believe that FS‐DSEK offers a great potential for facilitating endothelial keratoplasty in a more standardized, automated fashion. Longer‐term follow‐up will be necessary to assess final corneal graft clarity and visual outcome.

Dynamic Recompartmentalization of Supported Lipid Bilayers Using Focused Femtosecond Laser Pulses

H ow the presence,distributions,and dynam -ics of diffusionalbarriers influence B row nian m otions of lipids andproteins, however, remains poorly understood. To systematicallystudy these processes, model systems which exhibit dynamicmembrane compartmentalization are highly desirable.In a parallel line of research, ultrafast laser pulses (e.g.,fem tosecond) are proving to be valuable in inducing highly localizedphotomodifications in many soft materials including glasses,polymers, and cells.

Femtosecond-laser arcuate wedge-shaped resection to correct high residual astigmatism after penetrating keratoplasty

We describe a standardized technique of femtosecond (FS) laser arcuate resection (LAR) in which intersecting arcuate cuts are used to perform a wedge resection for the correction of high astigmatism. A simple formula was used to calculate the relative decentration of the arcuate cuts based on the radii of curvature and desired wedge width to be resected. Feasibility of the procedure was established in porcine corneas before treatment of a patient with 20 diopters (D) of post-keratoplasty astigmatism. The astigmatism was reversed. Suture removal resulted in reduction of 14.5 D of astigmatism. Laser arcuate resection can be an effective alternative to manual wedge resection, allowing easier, more controlled, and more precise excision of tissue in width, length, and depth.

A Femtosecond Laser Creates a Stronger Flap than a Mechanical Microkeratome

To compare corneal flaps made with a femtosecond (FS) laser with those made with a mechanical microkeratome (MM) in rabbits, measuring early postoperative inflammation and apoptosis and late postoperative adhesion strength. Study 1 involved four treatment groups: one with flaps made only with the FS laser (FS group), one with flaps made with the FS laser followed by excimer laser ablation (FS+LASIK), one with flaps made with the MM, and one with flaps made with the MM followed by excimer laser ablation (MM+LASIK). The eyes were analyzed by histology and TUNEL staining for apoptosis at 4 and 24 hours. Study 2 involved two reference groups: an FS group and an MM group. Adhesion strength was measured with a tension meter 1 and 3 months later. Study 1: Inflammatory cell infiltration in the central cornea was significantly greater in the FS group than in the MM group at 4 and 24 hours (P < 0.05) and was significantly greater in the FS+LASIK group than in the MM+LASIK group at 24 hours (P < 0.05). Infiltration at the peripheral interface was significantly greater in the FS group than in the MM group and was significantly greater in the FS+LASIK group than in the MM+LASIK group at 24 hours (P < 0.05). Study 2: At 1 and 3 months, 126.7 and 191.3 grams of force (gf) were needed to detach the flaps in the FS group, compared with 65 and 127.5 gf in the MM group, respectively. The grams of force needed was significantly higher in the FS group than in the MM group at 3 months (P < 0.05). The FS laser produces greater corneal stromal inflammation than the MM early postoperatively without any increase in apoptosis and stronger flap adhesion late postoperatively. Therefore, it may require stronger anti-inflammatory drugs to be administered.