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ABSTRACT: To investigate the relevance of initial temperature of the polymethylmethacrylate (PMMA) plates used as a target for photoablation during calibration of excimer lasers performed in daily clinical routine.
An experimental argon fluoride excimer laser with a repetition rate of 1050 Hz, a radiant exposure of 500 mJ/cm², and single pulse energy of 2.1 mJ was used for photoablation of PMMA plates. The initial plate temperature varied from 10.1°C to 75.7°C. The initial temperature was measured with an infrared camera and the central ablation depth of a myopic ablation of -9.00 diopters (D) with an optical zone of 6.5 mm was measured by means of a surface profiling system.
The ablation depth increased linearly from 73.9 to 96.3 μm within a temperature increase from 10.1°C to 75.7°C (increase rate of 0.3192 μm/K). The linear correlation was found to be significant (P<.05) with a coefficient of determination of R²=0.95. Based on these results and assuming a standard room temperature of 20°C, optimal plate temperature was calculated to be 15°C to 25°C to maintain an ablation within 0.25 D.
The temperature of PMMA plates for clinical laser calibration should be controlled ideally within a range of approximately ±5°C, to avoid visually significant refractive error due to calibration error. Further experimental investigations are required to determine the influence of different initial corneal temperatures on the refractive outcome.
Journal of refractive surgery (Thorofare, N.J.: 1995) 09/2012; 28(9):639-44. · 2.54 Impact Factor
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ABSTRACT: 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.
The British journal of ophthalmology 12/2011; 96(6):788-92. · 2.92 Impact Factor
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ABSTRACT: Purpose: To evaluate the safety, efficacy, predictability and stability of laser in situ keratomileusis (LASIK) with a 1000-Hz scanning spot excimer laser (Concept System 1000; WaveLight GmbH, Erlangen, Germany). Methods: LASIK was performed on twenty eyes with myopia or myopic astigmatism (mean spherical equivalent refraction: -3.97 ± 1.72 dioptres (D); mean cylinder: -0.84 ± 0.77 D) using a microkeratome for flap creation and the Concept System 1000 for photoablation. Patients were examined preoperatively as well as 1, 3 and 6 months after the treatment. Manifest sphere and cylinder, uncorrected (UCDVA) and best corrected (BCDVA) distance visual acuity, corneal topography and pachymetry were analysed. Results: We observed no adverse events that might have been associated with the use of a repetition rate of 1000 Hz. All eyes maintained or had improved BCDVA at 6 months after treatment when compared to preoperative values. Six months after LASIK, UCDVA was 20/20 or better in 85% and 20/25 or better in 100% of the eyes. The spherical equivalent refraction was within ±0.50 D in 95% of the eyes at 6 months after surgery. The refraction stayed stable over time; 95% of the eyes changed <0.5 D postoperatively. Conclusion: LASIK with the prototype 1000-Hz excimer laser was safe, efficient and predictable. The postoperative refraction was stable over time. There were no specific clinical side-effects that might be associated with the use of such a high repetition rate.
Acta ophthalmologica 01/2011; 90(6):508-13. · 2.44 Impact Factor
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ABSTRACT: To demonstrate the feasibility and technical features of the WaveLight FS200 femtosecond laser (WaveLight GmbH) in refractive and corneal laser surgery.
The reproducibility of femtosecond laser-created flap dimensions and channels used for corneal ring segment implantation were measured by means of an optical coherence tomography system in porcine corneas. The increase in the intraocular pressure (IOP) during applanation with the corneal interface was measured by means of an IOP sensor. The possibility of creating a channel for gas diffusion within the stroma was investigated to minimize opaque bubble layer formation.
The technical features, such as optical design, pulse energy, and scanning algorithms at a high repetition rate, allow reproducibility for tissue cutting with a standard deviation of <10 μm in depth and 0.1 mm laterally. Intraocular pressure increases up to 150 mmHg during applanation. The use of a gas channel minimizes the creation of an opaque bubble layer during the femtosecond laser procedure.
The WaveLight FS200 femtosecond laser provides a high reproducibility for cutting three-dimensional tissue structures. The IOP increase is comparable to other microkeratomes and femtosecond lasers. The minimized opaque bubble layers allow the surgeon to perform an excimer laser treatment immediately after FS200 flap creation.
Journal of refractive surgery (Thorofare, N.J.: 1995) 10/2010; 26(10):S833-40. · 2.54 Impact Factor
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ABSTRACT: To evaluate the possible side effects on human and porcine cadaver eyes induced by excimer laser ablation with 3 ablation frequencies.
Augenklinik, Klinikum rechts der Isar, Technische Universitaet Muenchen, Munich, Germany.
Central epithelial abrasion was performed on porcine and human donor eyes. Next, the porcine eyes were photoablated (-9.00 diopters) at 1 of 3 frequencies (200 Hz, 500 Hz, or 1000 Hz) using a prototype 1000 Hz excimer laser. The human eyes were ablated at 1000 Hz. The surface of the stroma as well as the structure and ultrastructure of the corneal cells and stroma were examined using light microscopy, transmission electron microscopy, and scanning electron microscopy (SEM). Special attention was given to the detection of potential thermal damage and the evaluation of corneal smoothness.
Histopathologic examination showed very low to almost no differences between the 3 repetition rates. In all cases, SEM showed an equally smooth surface.
The structural and ultrastructural evaluation of corneas treated with ablation frequencies of 200 Hz, 500 Hz, and 1000 Hz showed no specific side effects associated with the high repetition rates. The ablation quality was comparable in the 3 frequency groups. However, the treatment time was significantly less with a high repetition rate, indicating the clinical potential in refractive surgery of excimer lasers with a repetition rate of 1000 Hz.
No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.
Journal of cataract and refractive surgery 08/2010; 36(8):1385-91. · 2.75 Impact Factor
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ABSTRACT: To evaluate the safety, stability, and efficacy of the first clinical cases of epithelial laser in situ keratomileusis (epi-LASIK) performed using a 1000 Hz excimer laser system.
Klinikum Rechts der Isar, Munich, Germany.
The epi-LASIK procedure was performed using an EpiLift microkeratome and a WaveLight Concept System 1000 laser. Preoperatively and 1, 3, and 6 months postoperatively, a complete ophthalmic examination was performed. The examination included objective and subjective refraction, uncorrected and corrected distance visual acuities, and topography.
The study comprised 30 eyes of 17 patients. The mean spherical equivalent was -4.36 diopters (D) +/-1.77 (SD) preoperatively, 0.07 +/- 0.38 D 1 month postoperatively, -0.06 D +/- 0.25 D at 3 months, and -0.05 +/- 0.24 D at 6 months. Six months postoperatively, 90% of patients were within +/-0.50 D of the intended correction and all were within +/-1.00 D. At 3 months, 25 eyes had a clear cornea and 5 eyes had trace haze.
In this pilot series, the use of the 1000 Hz excimer laser did not lead to the clinical side effects that are potentially associated with the use of a high repetition rate. The safety, stability, and efficacy of the laser were high although no adjustments to the nomogram were made.
Journal of cataract and refractive surgery 03/2010; 36(3):449-55. · 2.75 Impact Factor
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ABSTRACT: To evaluate the feasibility of surface profiling for central ablation depth measurements and determine experimentally the required single-pulse energies and radiant exposures to achieve equivalent central ablation depths on bovine corneas for a myopic correction of -6.00 diopters (optical zone 6.5 mm) performed with laser repetition rates ranging from 100 to 1050 Hz.
Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland, and WaveLight AG, Erlangen, Germany.
Freshly enucleated bovine corneas and poly(methyl methacrylate) (PMMA) plates were photoablated. The shot pattern for the myopic correction was maintained during all experiments; the pulse laser energy was adjusted to achieve equal ablation depths for all repetition rates. Pulse energy, radiant exposure, and pulse duration were monitored to determine the required laser parameter.
The variations (standard deviation) of the profile measurements were +/-0.45 microm or less for PMMA and +/-1.50 microm or less for bovine corneas. Measurements with bovine corneas should be performed within 3 minutes or less to avoid larger variations in profile measurements. Increasing the repetition rate from 100 Hz to 1050 Hz required an increase in peak radiant exposure from 400 mJ/cm(2) to 530 mJ/cm(2) to achieve equal ablation for the myopic correction. The required increase in the mean radiant exposure ranged from 190 to 260 mJ/cm(2).
Higher-repetition-rate excimer lasers require increased radiant exposure. Further experimental studies should be performed to determine the relevance of spatial and temporal spot positioning, ablation-plume dynamics, and temperature increases during high-repetition-rate laser treatments.
Journal of cataract and refractive surgery 10/2009; 35(10):1806-14. · 2.75 Impact Factor
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ABSTRACT: To investigate the influence of temporal and spatial spot sequences on the ocular surface temperature increase during corneal laser surgery with a high-repetition-rate excimer laser.
Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland, and WaveLight AG, Erlangen, Germany.
An argon-fluoride excimer laser system working at a repetition rate of 1050 Hz was used to photoablate bovine corneas with various myopic, hyperopic, and phototherapeutic ablation profiles. The temporal distribution of ablation profiles was modified by 4 spot sequences: line, circumferential, random, and an optimized scan algorithm. The increase in ocular surface temperature was measured using an infrared camera.
The maximum and mean ocular surface temperature increases depended primarily on the spatial and temporal distribution of the spots during photoablation and the amount of refractive correction. The highest temperature increases were with the line and circumferential scan sequences. Significant lower temperature increases were found with the optimized and random scan algorithms.
High-repetition-rate excimer laser systems require spot sequences with optimized temporal and spatial spot distribution to minimize the increase in ocular surface temperature. An ocular surface temperature increase will always occur depending on the amount of refractive correction, the type of ablation profile, the radiant exposure, and the repetition rate of the laser system.
Journal of cataract and refractive surgery 05/2009; 35(4):738-46. · 2.75 Impact Factor
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ABSTRACT: To investigate the effect of temporal and spatial distributions of laser spots (scan sequences) on the corneal surface quality after ablation and the maximum ablation of a given refractive correction after photoablation with a high-repetition-rate scanning-spot laser.
IROC AG, Zurich, Switzerland, and WaveLight AG, Erlangen, Germany.
Bovine corneas and poly(methyl methacrylate) (PMMA) plates were photoablated using a 1050 Hz excimer laser prototype for corneal laser surgery. Four temporal and spatial spot distributions (scan sequences) with different temporal overlapping factors were created for 3 myopic, 3 hyperopic, and 3 phototherapeutic keratectomy ablation profiles. Surface quality and maximum ablation depth were measured using a surface profiling system.
The surface quality factor increased (rough surfaces) as the amount of temporal overlapping in the scan sequence and the amount of correction increased. The rise in surface quality factor was less for bovine corneas than for PMMA. The scan sequence might cause systematic substructures at the surface of the ablated material depending on the overlapping factor. The maximum ablation varied within the scan sequence.
The temporal and spatial distribution of the laser spots (scan sequence) during a corneal laser procedure affected the surface quality and maximum ablation depth of the ablation profile. Corneal laser surgery could theoretically benefit from smaller spot sizes and higher repetition rates. The temporal and spatial spot distributions are relevant to achieving these aims.
Journal of cataract and refractive surgery 03/2009; 35(2):363-73. · 2.75 Impact Factor
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ABSTRACT: Optical calculations have shown that wavefront-based ablation profiles as well as intraocular lens (IOL) implantations can cause residual aberrations or even induce significant additional aberrations due to the poor registry between the eye's optical components. These effects can be exacerbated in eyes that require higher corrections. Individualized eye models can provide accurate ablation profiles for these cases. The aim of this report is to analyze the relevance of individualized eye models for refractive treatment planning from a theoretical point of view.
A method for the customization of eye models based on various types of measurement data of a specific patient is presented and the calculation of optimal ablation profiles and IOL shapes by means of ray tracing through customized model eyes are discussed. Topography data with an original centration on the corneal apex were aligned on the pupil center for the creation of eye models.
An ideal ablation profile or a customized IOL can be calculated based on the obtained individualized eye models. Calculations have shown that in theory ray-tracing optimized ablation profiles do not leave any residual aberrations in the eye whereas wavefront-guided corrections were found to have the potential to increase specific types of aberrations by a factor of two. This is due to the negligence of the multi-lens structure of the eye.
Optical ray tracing algorithms allow the highest degree of customization. The systematic induction of higher order aberrations by means of wavefront-guided treatments or standard IOLs has to be overcome by such a method. However, these theoretical observations must be compared to the corresponding measurement accuracies and precisions and they must be supported by future clinical trials.
Journal of refractive surgery (Thorofare, N.J.: 1995) 05/2008; 24(4):S446-51. · 2.54 Impact Factor
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ABSTRACT: To evaluate the efficacy of customized surface ablation in cases of forme fruste keratoconus.
Prospective noncomparative case series.
Eleven eyes of 8 contact lens-intolerant patients with forme fruste keratoconus treated at the Institute of Refractive and Ophthalmic Surgery and the University Eye Clinic Zurich.
Topography-guided customized surface ablation by means of a scanning spot excimer laser.
Visual acuity, refraction, quality of vision (ghosting), corneal topography including the Zernike parameter Z3.
Statistically significant reduction of manifest refractive error, corneal irregularity, and ghosting. The spherical equivalent was reduced by -2.8+/-0.62 diopters (D) (P = 0.0007), the cylinder by 1.34 +/- 0.18 D (P = 0.015), Z3 was reduced by 41% (P<0.001), and all patients had less ghosting compared to their preoperative status. No eye lost > or =1 lines in best spectacle-corrected visual acuity; however, 7 of 11 eyes gained > or = 1 line.
Topography-guided surface ablation is a promising option to rehabilitate vision in contact lens-intolerant patients with forme fruste keratoconus.
Ophthalmology 12/2006; 113(12):2198-202. · 5.45 Impact Factor
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ABSTRACT: To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections.
IROC-Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland.
The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of "classic" ablation profiles for myopic and astigmatic corrections.
The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction.
Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.
Journal of Cataract [?] Refractive Surgery 05/2004; 30(4):775-85. · 2.26 Impact Factor
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ABSTRACT: Laser epithelial keratomileusis (LASEK) is a technique of refractive surgery for treatment of myopia. More than 90% of patients are within the intended correction of +/-0.50 diopters (D), without any unwanted side effects. After conventional refractive surgery, higher-order aberrations are induced. To reduce these aberrations, we used wavefront-guided ablation.
Twenty patients with visual problems in ambient light were included. The primary surgery was 141 to 463 days before the retreatment. LASEK was performed with the Camellin technique with 20% EtOH for 30 seconds. Before surgery, the root mean square (RMS) values were measured and the laser treatment was performed with the WaveLight Concept System 500 (WaveLight Laser Technologie AG). The preoperative spherical equivalent refraction was -1.22 D (SD 0.57 D) and the astigmatism was -0.42 D (SD 0.25 D). Preoperatively and 6 months postoperatively, a comprehensive examination was performed.
All retreatments were performed without any intra- or postoperative complications. All patients reported an improvement of vision. The 6-month postoperative refraction was 0.25 D (SD 0.36 D). RMS decreased significantly from 0.72 to 0.47. RMS fourth order also decreased significantly from 0.60 to 0.30 and the spherical aberration decreased significantly from 0.57 to 0.28.
In earlier studies, patients reported reduction of contrast vision, even after resurgery. Our patients showed a significant reduction of higher-order aberrations and better contrast vision after retreatment with wavefront guided LASEK. Retreatment with wavefront-guided LASEK has the potential to correct night vision problems after excimer laser surgery.
Journal of refractive surgery (Thorofare, N.J.: 1995) 20(5):S565-9. · 2.54 Impact Factor
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ABSTRACT: We report on laser safety aspects for near infrared femtosecond laser refractive surgery. In particular, the transmittance of microjoule laser pulses at 1040 nm through the cornea during flap procedures based on femtosecond laser induced multiphoton ionization and photodisruption has been determined. When using focusing optics with a numerical aperture of 0.3, more than 20% of the incident NIR photons are propagating towards the retina. In addition, self-focusing, white light and second harmonic generation, and destructive photodisruptive side effects have to be considered when using such high energy laser pulses of amplified laser systems. Microjoule femtosecond laser pulses in combination with low NA objectives have the potential to induce destructive intraocular side effects. Further studies are required to evaluate the damage potential of the transmitted photons absorbed by the retinal pigment epithelium and other intraocular compartments. Because of the fact that flaps can be also generated with low nanojoule energy femtosecond laser pulses of non-amplified MHz lasers in combination with high NA objectives, a compromise between procedure time, pulse energy and numerical apertures has to be found for safe ocular femtosecond laser surgery.ZusammenfassungWir berichten über Lasersicherheitsaspekte für refraktive nahe-infrarote Femtosekundenlaser-Laserchirurgie. Insbesondere wurden die Werte der Cornea-Transmission von Mikrojoule-Laserpulsen bei einer Wellenlänge von 1040 nm während der Flap-Herstellung mittels Femtosekundenlaser-induzierter Multiphotonen-Ionisation und Photodisruption bestimmt. Mehr als 20% der einfallenden Photonen propagieren in Richtung Retina, wenn Fokussieroptiken der numerischen Apertur 0,3 verwendet werden. Durch die Verwendung hochenergetischer Laserpulse verstärkter Lasersysteme müssen zusätzlich Selbstfokussierung, Weisslicht-Generation und SHG-Erzeugung sowie destruktive photodisruptive Nebeneffekte berücksichtigt werden. Mikrojoule Femtosekunden-Laserpulse in Kombination mit Objektiven geringer NA besitzen das Potential, destruktive intraokulare Nebeneffekte hervorzurufen. Weitere Studien sind erforderlich, um das Schädigungspotential der transmittierten Photonen, die vom retinalen Pigmentepithel und anderen Intraokular-Bereichen absorbiert werden, zu evaluieren. Da Flaps auch mit Femtosekunden-Laserpulsen unverstärkter MHz Lasersysteme geringer Nanojoule Pulsenergie in Kombination mit Objektiven hoher NA hergestellt werden können, sollte ein Kompromiss bezüglich der Behandlungsdauer, der Pulsenergie und der numerischen Apertur für eine sichere Femtosekundenlaser-Augenchirurgie gefunden werden.
Medical Laser Application.
