Tibor Juhasz - Academia.edu (original) (raw)

Papers by Tibor Juhasz

IEEE Ultrasonics Symposium, 2004, 2004

We test the hypothesis that local viscoelastic properties of the intraocular lens can be measured... more We test the hypothesis that local viscoelastic properties of the intraocular lens can be measured by applying acoustic radiation force to laser-generated bubbles. Presbyopia is an age-related condition resulting from increased stiffness of the lens, reducing its ability to accommodate. A technique to measure local lens viscoelastic properties is needed to better understand the onset of presbyopia and guide potential correction procedures. Laser-induced optical breakdown (LIOB) is used to create bubbles within porcine intraocular lenses. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. The small transient gas bubbles can be used as targets for acoustic radiation force measurements prior to their ultimate collapse. While ultrasonic speckle is extremely limited within the lens, LIOB bubbles provide strong ultrasonic backscatter to measure lens viscoelastic properties. In this investigation, explanted porcine lenses are embedded within a gelatin phantom (5 w/w%) prior to laser treatment. An integrated optical-acoustical system has been constructed enabling simultaneous bubble creation and radiation force experiments. A two-element confocal ultrasonic transducer generates acoustic radiation force with the 1.5 MHz outer element while monitoring the bubble displacement within the lens using the 7.44 MHz inner element. Preliminary experiments have demonstrated the ability to create LIOB bubbles within explanted porcine lenses with lifetimes on the order of a few minutes and at any depth within the lens. Acoustic radiation force experiments with LIOB bubbles in porcine lenses exhibit exponential responses with time constants near 2 ms and maximum displacements on the order of 100 μm. These results advance the development of an in vivo technique to measure local lens viscoelastic properties.

Ultrasound in Medicine & Biology, 2014

To investigate the role of collagen structure in corneal biomechanics, measurement of localized c... more To investigate the role of collagen structure in corneal biomechanics, measurement of localized corneal elasticity with minimal destruction to the tissue is necessary. We adopted the recently developed acoustic radiation force elastic microscopy (ARFEM) technique to measure localize biomechanical properties of the human cornea. In ARFEM, a low-frequency, high-intensity acoustic force is used to displace a femtosecond laser-generated microbubble, while high-frequency, low-intensity ultrasound is used to monitor the position of the microbubble within the cornea. Two ex vivo human corneas from a single donor were dehydrated to physiologic thickness, embedded in gelatin and then evaluated using the ARFEM technique. In the direction perpendicular to the corneal surface, ARFEM measurements provided elasticity values of E = 1.39 ± 0.28 kPa for the central anterior cornea and E = 0.71 ± 0.21 kPa for the central posterior cornea in pilot studies. The increased value of corneal elasticity in the anterior cornea correlates with the higher density of interweaving lamellae in this region.

Journal of Biomedical Optics, 2014

Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and i... more Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuriesin the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential useof laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ = 2.94 μm), titanium:sapphire femtosecond laser system (λ = 1700 nm), and Nd:glass femtosecond laser (λ = 1053 nm). Bovine samples were ablated at fluences of 8 to 18 J∕cm2 with the erbium:YAG laser, at a power of 300 ± 15 mW with the titanium:sapphire femtosecond system, and at an energy of 3 μJ∕pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18 J∕cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates.

Optics and Photonics News, 2002

Surgeons use a number of devices to create incisions in tissue. These include steel and gem blade... more Surgeons use a number of devices to create incisions in tissue. These include steel and gem blades, radio frequency, high-pressure waterjet, and electrocautery technologies. Interestingly, while lasers have an established place in the operating room, as cutting ...

Ophthalmic Technologies XIV, 2004

A finite element method was used to study the biomechanical behavior of the cornea and its respon... more A finite element method was used to study the biomechanical behavior of the cornea and its response to refractive surgery when stiffness inhomogeneities varying with depth are considered. Side-by-side comparisons of different constitutive laws that have been commonly used to model refractive surgery were also performed. To facilitate the comparison, the material property constants were identified from the same experimental

Commercial and Biomedical Applications of Ultrafast Lasers, 1999

ABSTRACT

Ophthalmology, 2005

To perfect the technique of femtosecond laser-assisted cutting of the lamellar corneal disc in po... more To perfect the technique of femtosecond laser-assisted cutting of the lamellar corneal disc in posterior lamellar keratoplasty. Experimental study. The femtosecond laser was used to make the posterior corneal lamellar interface and trephine (side) cut in 20 eye bank globes and 9 eye bank corneoscleral buttons. Laser parameters were energy 7.4+/-0.1 microJ (lamellar cut) and 8.7+/-0.1 microJ (trephination cut), spot size 2.4 microm, firing rate 15 kHz, and trephination diameter 6.0 to 8.0 mm. The thicknesses of the excised corneal discs were measured with a digital micrometer and compared with values calculated from the laser treatment parameters and the preoperative ultrasound pachymetric readings. The cut surfaces were examined by light microscopy and scanning electron microscopy. In globes, the corneal disc was removed from the eye after laser treatment through a blade incision in the peripheral cornea. In corneoscleral buttons, the posterior disc was peeled off the cornea with forceps after laser treatment on an artificial anterior chamber device. In simulated transplantation, the excised corneal disc was placed into the posterior stromal bed in 7 globes. The femtosecond laser was successful in making posterior lamellar and trephination cuts in cornea. The cut surfaces were of very good quality with straight, orthogonal edges, albeit with a mild stucco texture of the lamellar stromal surfaces. In 3 globes, the lamellar surface showed shallow concentric ridges. The measured thickness of the excised discs was 55+/-61 microm thicker than the preoperatively predicted values. These preliminary studies show that the femtosecond laser can make nonmechanical cuts for posterior lamellar keratoplasty with relative ease and reliability, thus facilitating the most technically difficult step in this surgery.

Ophthalmic Technologies IX, 1999

ABSTRACT

Ophthalmic Research, 2006

To estimate the theoretical corneal refractive error induced by mechanical weakening effects from... more To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. The predicted refractive change after PLKP is less than 1 dpt for a 170-microm thickness posterior corneal button over a broad range of Young's modulus. Thicker buttons result in greater surgically induced refractive errors. According to FEM analysis, the excision of a posterior lamellar button of less than 170 microm thickness produces a minimal predicted refractive change (< 1 dpt) in the cornea after PLKP.

Ophthalmic Research, 2006

To estimate the theoretical corneal refractive error induced by mechanical weakening effects from... more To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. The predicted refractive change after PLKP is less than 1 dpt for a 170-microm thickness posterior corneal button over a broad range of Young's modulus. Thicker buttons result in greater surgically induced refractive errors. According to FEM analysis, the excision of a posterior lamellar button of less than 170 microm thickness produces a minimal predicted refractive change (< 1 dpt) in the cornea after PLKP.

Lasers in Surgery and Medicine, 2008

Partial thickness drainage channels can be created with femtosecond lasers in the translucent scl... more Partial thickness drainage channels can be created with femtosecond lasers in the translucent sclera for the potential treatment of glaucoma. We present a 3D finite element model (FEM) that can predict the effect of these channels on aqueous humor (AH) outflow and intraocular pressure (IOP). A 3D model was developed based on a 2D model for the intact eye using COMSOL (Comsol, Inc., MA) finite element software. Different values of permeability were entered into the 3D model for the AH pathway and for the partial thickness channel. To obtain experimental data for model validation, one partial thickness channel was created in each of three enucleated rabbit eyes with a femtosecond laser tuned to 1.7 microm wavelength. Aqueous outflow rates were measured with the perfusion method before and after the laser treatments at different levels of IOP and then compared to IOP values predicted by the model. The experiments indicated that the rate of the AH outflow was increased in each of three eyes after the laser treatment. Assuming a constant rate of AH production the 3D model predicted IOP reductions ranging from 67.2% to 80.6% as the effect of the laser created channels. These predictions were in reasonable agreement with experimentally adjusted IOP values during the perfusion measurements. The developed 3D FEM has the potential to predict IOP reduction caused by partial thickness drainage channels created with the femtosecond laser in the sclera. Such a model may also be used to determine optimal channel dimensions for a specified increase in outflow facility and reduction in IOP.

Lasers in Surgery and Medicine, 1996

Lasers in Surgery and Medicine, 1996

Journal of Cataract & Refractive Surgery, 2014

To analyze complications of femtosecond lasers used for cataract surgery. Department of Ophthalmo... more To analyze complications of femtosecond lasers used for cataract surgery. Department of Ophthalmology Semmelweis University, Budapest, Hungary. Retrospective analysis. Intraoperative complications of the first 100 femtosecond laser-assisted (Alcon-Lensx, Inc.) cataract surgeries were collected. Possible complications of femtosecond capsulotomies and their management were also assessed. The complications were as follows: suction break (2%), conjunctival redness or hemorrhage (34%), capsule tags and bridges (20%), anterior tear (4%), miosis (32%), and endothelial damage due to cut within the endothelial layer (3%). There were no cases of capsule blockage or posterior capsule tear. During the learning curve, there was no complication that would require vitrectomy. All complications occurred during the first 100 cases. Femtosecond laser cataract surgery had a learning curve during the first 100 cases. With cautious surgical technique, the complications can be avoided. The femtosecond laser-assisted method was efficient and safe for cataract surgery.

Lasers in Surgery and Medicine, 2010

The progression of glaucoma can be reduced or delayed by reducing intraocular pressure (IOP). The... more The progression of glaucoma can be reduced or delayed by reducing intraocular pressure (IOP). The properties of femtosecond laser surgery, such as markedly reduced collateral tissue damage, coupled with the ability to achieve isolated subsurface surgical effects in the sclera, make this technology a promising candidate in glaucoma management. In this pilot study we demonstrate the in vivo creation of partial thickness subsurface drainage channels with the femtosecond laser in the sclera of rabbit eyes in order to increase aqueous humor (AH) outflow. A femtosecond laser beam tuned to a 1.7 microm wavelength was scanned along a rectangular raster pattern to create the partial thickness subsurface drainage channels in the sclera of one eye of each of the four rabbits included in this pilot study. IOP was measured before and 20 minutes after the laser treatment to evaluate the acute effect of the procedure. OCT images verified the creation of the partial thickness subsurface scleral channels in the eyes of the in vivo rabbits. Comparison of pre- and postoperative IOP measurements in treated and control eyes revealed a reduction in the intraocular pressure due to the increased rate of AH outflow resulted in by the presence of the partial thickness scleral channels. The creation of partial thickness subsurface drainage channels was demonstrated in the sclera of in vivo rabbit eyes with a 1.7 microm wavelength femtosecond laser. Reduction in IOP achieved by the partial thickness channels suggests potential utility in the treatment of elevated IOP.

Journal of Cataract & Refractive Surgery, 2011

To measure the temperature rise in porcine cadaver iris during direct illumination by the femtose... more To measure the temperature rise in porcine cadaver iris during direct illumination by the femtosecond laser as a model for laser exposure of the iris during femtosecond laser corneal surgery. Department of Ophthalmology, University of California-Irvine, Irvine, California, USA. Experimental study. The temperature increase induced by a 60 kHz commercial femtosecond laser in porcine cadaver iris was measured in situ using an infrared thermal imaging camera at pulse energy levels ranging from 1 to 2 μJ (corresponding approximately to surgical energies of 2 to 4 μJ per laser pulse). Temperature increases up to 2.3 °C (corresponding to 2 μJ and 24-second illumination) were observed in the porcine cadaver iris with little variation in temperature profiles between specimens for the same laser energy illumination. The 60 kHz commercial femtosecond laser operating with pulse energies at approximately the lower limit of the range evaluated in this study would be expected to result in a 1.2 °C temperature increase and therefore does not present a safety hazard to the iris.

European Journal of Paediatric Neurology, 1998

Femtosecond lasers emitting in the wavelength range around 1 μm are attractive sources for a vari... more Femtosecond lasers emitting in the wavelength range around 1 μm are attractive sources for a variety of applications. At 1.06 μm, neodymium-doped glass offers both the relatively broad gain bandwidth, which is necessary for femtosecond pulse generation, and a strong absorption band around 800 nm, which allows for direct diode-pumping. Femtosecond pulses from diode-pumped Nd:glass lasers were previously reported, using

Journal of Cataract & Refractive Surgery, 2005

To measure and compare the changes in objective wavefront aberration and subjective manifest refr... more To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser. Private practice refractive surgery center, Irvine, California, USA. This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation. Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar. The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.

The European Physical Journal Applied Physics, 2005

... APPLIED PHYSICS Dynamics of shock waves and cavitation bubbles in bilinear ... 42.55.-f Laser... more ... APPLIED PHYSICS Dynamics of shock waves and cavitation bubbles in bilinear ... 42.55.-f Lasers – 43.25.Vt Intense sound sources – 43.25.Yw Acoustic cavitation, vibration of gas bubbles in liquids – 43.40.Ng Effects of vibration and shock on biological systems, including man ...

Journal of Cataract & Refractive Surgery, 2008

To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created ... more To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created using an IntraLase femtosecond laser (IntraLase, Inc.) with a 60 kHz engine. Laser suite in a clinical practice. A LASIK flap was created in 4 human eye-bank eyes using the 60 kHz IntraLase femtosecond laser with the following settings: 110 microm flap thickness, 9.0 mm flap diameter, 60-degree hinge length, 65-degree side cut, 0.4 muJ or 0.7 muJ raster energy, 7 microm x 7 microm or 9 microm x 9 microm spot/line separation, and 1 muJ side-cut energy. Immediately after the laser pass and without the flap being lifted, the globes were placed in fixative and subsequently processed for light and transmission electron microscopy. All 4 procedures were completed without complications or the appearance of an opaque bubble layer. The flaps were of uniform thickness and equaled the attempted thickness. Some areas had a complete dissection; other areas had scattered, incomplete tissue bridges. The adjacent corneal stroma and keratocytes were uninjured. When the epithelium was removed, the stromal component of the flap was measured as the attempted thickness; when the epithelium was present, the total flap thickness approximated the attempted flap thickness. Laser in situ keratomileusis flaps were safely created using raster energies and laser spot separations below those being used clinically. This technique may allow creation of flaps that are reproducibly thinner than those currently being performed and thus confer the benefits of surface ablation and LASIK.

IEEE Ultrasonics Symposium, 2004, 2004

We test the hypothesis that local viscoelastic properties of the intraocular lens can be measured... more We test the hypothesis that local viscoelastic properties of the intraocular lens can be measured by applying acoustic radiation force to laser-generated bubbles. Presbyopia is an age-related condition resulting from increased stiffness of the lens, reducing its ability to accommodate. A technique to measure local lens viscoelastic properties is needed to better understand the onset of presbyopia and guide potential correction procedures. Laser-induced optical breakdown (LIOB) is used to create bubbles within porcine intraocular lenses. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. The small transient gas bubbles can be used as targets for acoustic radiation force measurements prior to their ultimate collapse. While ultrasonic speckle is extremely limited within the lens, LIOB bubbles provide strong ultrasonic backscatter to measure lens viscoelastic properties. In this investigation, explanted porcine lenses are embedded within a gelatin phantom (5 w/w%) prior to laser treatment. An integrated optical-acoustical system has been constructed enabling simultaneous bubble creation and radiation force experiments. A two-element confocal ultrasonic transducer generates acoustic radiation force with the 1.5 MHz outer element while monitoring the bubble displacement within the lens using the 7.44 MHz inner element. Preliminary experiments have demonstrated the ability to create LIOB bubbles within explanted porcine lenses with lifetimes on the order of a few minutes and at any depth within the lens. Acoustic radiation force experiments with LIOB bubbles in porcine lenses exhibit exponential responses with time constants near 2 ms and maximum displacements on the order of 100 μm. These results advance the development of an in vivo technique to measure local lens viscoelastic properties.

Ultrasound in Medicine & Biology, 2014

To investigate the role of collagen structure in corneal biomechanics, measurement of localized c... more To investigate the role of collagen structure in corneal biomechanics, measurement of localized corneal elasticity with minimal destruction to the tissue is necessary. We adopted the recently developed acoustic radiation force elastic microscopy (ARFEM) technique to measure localize biomechanical properties of the human cornea. In ARFEM, a low-frequency, high-intensity acoustic force is used to displace a femtosecond laser-generated microbubble, while high-frequency, low-intensity ultrasound is used to monitor the position of the microbubble within the cornea. Two ex vivo human corneas from a single donor were dehydrated to physiologic thickness, embedded in gelatin and then evaluated using the ARFEM technique. In the direction perpendicular to the corneal surface, ARFEM measurements provided elasticity values of E = 1.39 ± 0.28 kPa for the central anterior cornea and E = 0.71 ± 0.21 kPa for the central posterior cornea in pilot studies. The increased value of corneal elasticity in the anterior cornea correlates with the higher density of interweaving lamellae in this region.

Journal of Biomedical Optics, 2014

Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and i... more Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuriesin the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential useof laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ = 2.94 μm), titanium:sapphire femtosecond laser system (λ = 1700 nm), and Nd:glass femtosecond laser (λ = 1053 nm). Bovine samples were ablated at fluences of 8 to 18 J∕cm2 with the erbium:YAG laser, at a power of 300 ± 15 mW with the titanium:sapphire femtosecond system, and at an energy of 3 μJ∕pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18 J∕cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates.

Optics and Photonics News, 2002

Surgeons use a number of devices to create incisions in tissue. These include steel and gem blade... more Surgeons use a number of devices to create incisions in tissue. These include steel and gem blades, radio frequency, high-pressure waterjet, and electrocautery technologies. Interestingly, while lasers have an established place in the operating room, as cutting ...

Ophthalmic Technologies XIV, 2004

A finite element method was used to study the biomechanical behavior of the cornea and its respon... more A finite element method was used to study the biomechanical behavior of the cornea and its response to refractive surgery when stiffness inhomogeneities varying with depth are considered. Side-by-side comparisons of different constitutive laws that have been commonly used to model refractive surgery were also performed. To facilitate the comparison, the material property constants were identified from the same experimental

Commercial and Biomedical Applications of Ultrafast Lasers, 1999

ABSTRACT

Ophthalmology, 2005

To perfect the technique of femtosecond laser-assisted cutting of the lamellar corneal disc in po... more To perfect the technique of femtosecond laser-assisted cutting of the lamellar corneal disc in posterior lamellar keratoplasty. Experimental study. The femtosecond laser was used to make the posterior corneal lamellar interface and trephine (side) cut in 20 eye bank globes and 9 eye bank corneoscleral buttons. Laser parameters were energy 7.4+/-0.1 microJ (lamellar cut) and 8.7+/-0.1 microJ (trephination cut), spot size 2.4 microm, firing rate 15 kHz, and trephination diameter 6.0 to 8.0 mm. The thicknesses of the excised corneal discs were measured with a digital micrometer and compared with values calculated from the laser treatment parameters and the preoperative ultrasound pachymetric readings. The cut surfaces were examined by light microscopy and scanning electron microscopy. In globes, the corneal disc was removed from the eye after laser treatment through a blade incision in the peripheral cornea. In corneoscleral buttons, the posterior disc was peeled off the cornea with forceps after laser treatment on an artificial anterior chamber device. In simulated transplantation, the excised corneal disc was placed into the posterior stromal bed in 7 globes. The femtosecond laser was successful in making posterior lamellar and trephination cuts in cornea. The cut surfaces were of very good quality with straight, orthogonal edges, albeit with a mild stucco texture of the lamellar stromal surfaces. In 3 globes, the lamellar surface showed shallow concentric ridges. The measured thickness of the excised discs was 55+/-61 microm thicker than the preoperatively predicted values. These preliminary studies show that the femtosecond laser can make nonmechanical cuts for posterior lamellar keratoplasty with relative ease and reliability, thus facilitating the most technically difficult step in this surgery.

Ophthalmic Technologies IX, 1999

ABSTRACT

Ophthalmic Research, 2006

To estimate the theoretical corneal refractive error induced by mechanical weakening effects from... more To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. The predicted refractive change after PLKP is less than 1 dpt for a 170-microm thickness posterior corneal button over a broad range of Young's modulus. Thicker buttons result in greater surgically induced refractive errors. According to FEM analysis, the excision of a posterior lamellar button of less than 170 microm thickness produces a minimal predicted refractive change (< 1 dpt) in the cornea after PLKP.

Ophthalmic Research, 2006

To estimate the theoretical corneal refractive error induced by mechanical weakening effects from... more To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. The predicted refractive change after PLKP is less than 1 dpt for a 170-microm thickness posterior corneal button over a broad range of Young's modulus. Thicker buttons result in greater surgically induced refractive errors. According to FEM analysis, the excision of a posterior lamellar button of less than 170 microm thickness produces a minimal predicted refractive change (< 1 dpt) in the cornea after PLKP.

Lasers in Surgery and Medicine, 2008

Partial thickness drainage channels can be created with femtosecond lasers in the translucent scl... more Partial thickness drainage channels can be created with femtosecond lasers in the translucent sclera for the potential treatment of glaucoma. We present a 3D finite element model (FEM) that can predict the effect of these channels on aqueous humor (AH) outflow and intraocular pressure (IOP). A 3D model was developed based on a 2D model for the intact eye using COMSOL (Comsol, Inc., MA) finite element software. Different values of permeability were entered into the 3D model for the AH pathway and for the partial thickness channel. To obtain experimental data for model validation, one partial thickness channel was created in each of three enucleated rabbit eyes with a femtosecond laser tuned to 1.7 microm wavelength. Aqueous outflow rates were measured with the perfusion method before and after the laser treatments at different levels of IOP and then compared to IOP values predicted by the model. The experiments indicated that the rate of the AH outflow was increased in each of three eyes after the laser treatment. Assuming a constant rate of AH production the 3D model predicted IOP reductions ranging from 67.2% to 80.6% as the effect of the laser created channels. These predictions were in reasonable agreement with experimentally adjusted IOP values during the perfusion measurements. The developed 3D FEM has the potential to predict IOP reduction caused by partial thickness drainage channels created with the femtosecond laser in the sclera. Such a model may also be used to determine optimal channel dimensions for a specified increase in outflow facility and reduction in IOP.

Lasers in Surgery and Medicine, 1996

Lasers in Surgery and Medicine, 1996

Journal of Cataract & Refractive Surgery, 2014

To analyze complications of femtosecond lasers used for cataract surgery. Department of Ophthalmo... more To analyze complications of femtosecond lasers used for cataract surgery. Department of Ophthalmology Semmelweis University, Budapest, Hungary. Retrospective analysis. Intraoperative complications of the first 100 femtosecond laser-assisted (Alcon-Lensx, Inc.) cataract surgeries were collected. Possible complications of femtosecond capsulotomies and their management were also assessed. The complications were as follows: suction break (2%), conjunctival redness or hemorrhage (34%), capsule tags and bridges (20%), anterior tear (4%), miosis (32%), and endothelial damage due to cut within the endothelial layer (3%). There were no cases of capsule blockage or posterior capsule tear. During the learning curve, there was no complication that would require vitrectomy. All complications occurred during the first 100 cases. Femtosecond laser cataract surgery had a learning curve during the first 100 cases. With cautious surgical technique, the complications can be avoided. The femtosecond laser-assisted method was efficient and safe for cataract surgery.

Lasers in Surgery and Medicine, 2010

The progression of glaucoma can be reduced or delayed by reducing intraocular pressure (IOP). The... more The progression of glaucoma can be reduced or delayed by reducing intraocular pressure (IOP). The properties of femtosecond laser surgery, such as markedly reduced collateral tissue damage, coupled with the ability to achieve isolated subsurface surgical effects in the sclera, make this technology a promising candidate in glaucoma management. In this pilot study we demonstrate the in vivo creation of partial thickness subsurface drainage channels with the femtosecond laser in the sclera of rabbit eyes in order to increase aqueous humor (AH) outflow. A femtosecond laser beam tuned to a 1.7 microm wavelength was scanned along a rectangular raster pattern to create the partial thickness subsurface drainage channels in the sclera of one eye of each of the four rabbits included in this pilot study. IOP was measured before and 20 minutes after the laser treatment to evaluate the acute effect of the procedure. OCT images verified the creation of the partial thickness subsurface scleral channels in the eyes of the in vivo rabbits. Comparison of pre- and postoperative IOP measurements in treated and control eyes revealed a reduction in the intraocular pressure due to the increased rate of AH outflow resulted in by the presence of the partial thickness scleral channels. The creation of partial thickness subsurface drainage channels was demonstrated in the sclera of in vivo rabbit eyes with a 1.7 microm wavelength femtosecond laser. Reduction in IOP achieved by the partial thickness channels suggests potential utility in the treatment of elevated IOP.

Journal of Cataract & Refractive Surgery, 2011

To measure the temperature rise in porcine cadaver iris during direct illumination by the femtose... more To measure the temperature rise in porcine cadaver iris during direct illumination by the femtosecond laser as a model for laser exposure of the iris during femtosecond laser corneal surgery. Department of Ophthalmology, University of California-Irvine, Irvine, California, USA. Experimental study. The temperature increase induced by a 60 kHz commercial femtosecond laser in porcine cadaver iris was measured in situ using an infrared thermal imaging camera at pulse energy levels ranging from 1 to 2 μJ (corresponding approximately to surgical energies of 2 to 4 μJ per laser pulse). Temperature increases up to 2.3 °C (corresponding to 2 μJ and 24-second illumination) were observed in the porcine cadaver iris with little variation in temperature profiles between specimens for the same laser energy illumination. The 60 kHz commercial femtosecond laser operating with pulse energies at approximately the lower limit of the range evaluated in this study would be expected to result in a 1.2 °C temperature increase and therefore does not present a safety hazard to the iris.

European Journal of Paediatric Neurology, 1998

Femtosecond lasers emitting in the wavelength range around 1 μm are attractive sources for a vari... more Femtosecond lasers emitting in the wavelength range around 1 μm are attractive sources for a variety of applications. At 1.06 μm, neodymium-doped glass offers both the relatively broad gain bandwidth, which is necessary for femtosecond pulse generation, and a strong absorption band around 800 nm, which allows for direct diode-pumping. Femtosecond pulses from diode-pumped Nd:glass lasers were previously reported, using

Journal of Cataract & Refractive Surgery, 2005

To measure and compare the changes in objective wavefront aberration and subjective manifest refr... more To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser. Private practice refractive surgery center, Irvine, California, USA. This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation. Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar. The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.

The European Physical Journal Applied Physics, 2005

... APPLIED PHYSICS Dynamics of shock waves and cavitation bubbles in bilinear ... 42.55.-f Laser... more ... APPLIED PHYSICS Dynamics of shock waves and cavitation bubbles in bilinear ... 42.55.-f Lasers – 43.25.Vt Intense sound sources – 43.25.Yw Acoustic cavitation, vibration of gas bubbles in liquids – 43.40.Ng Effects of vibration and shock on biological systems, including man ...

Journal of Cataract & Refractive Surgery, 2008

To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created ... more To document the acute morphologic features of laser of situ keratomileusis (LASIK) flaps created using an IntraLase femtosecond laser (IntraLase, Inc.) with a 60 kHz engine. Laser suite in a clinical practice. A LASIK flap was created in 4 human eye-bank eyes using the 60 kHz IntraLase femtosecond laser with the following settings: 110 microm flap thickness, 9.0 mm flap diameter, 60-degree hinge length, 65-degree side cut, 0.4 muJ or 0.7 muJ raster energy, 7 microm x 7 microm or 9 microm x 9 microm spot/line separation, and 1 muJ side-cut energy. Immediately after the laser pass and without the flap being lifted, the globes were placed in fixative and subsequently processed for light and transmission electron microscopy. All 4 procedures were completed without complications or the appearance of an opaque bubble layer. The flaps were of uniform thickness and equaled the attempted thickness. Some areas had a complete dissection; other areas had scattered, incomplete tissue bridges. The adjacent corneal stroma and keratocytes were uninjured. When the epithelium was removed, the stromal component of the flap was measured as the attempted thickness; when the epithelium was present, the total flap thickness approximated the attempted flap thickness. Laser in situ keratomileusis flaps were safely created using raster energies and laser spot separations below those being used clinically. This technique may allow creation of flaps that are reproducibly thinner than those currently being performed and thus confer the benefits of surface ablation and LASIK.