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Nd:glass femtosecond laser is promising as next generation mini-invasive eye surgical laser, with the advantages of excellent beam quality, high surgical precision and minimized side effects. However, there are still many open questions concerning the precision, efficiency and collateral effects of femtosecond laser refractive surgery. By non-invasive microscopic imaging methods including confocal, multiphoton, second harmonic and atomic force microscopy, we successfully characterized the three dimensional corneal ultrastructure without applying fixation and slicing. Based on the intrinsic properties of collagen, second harmonic cornea imaging proved to be outstanding to analyze the outcome of femtosecond laser intrastromal ablations. Strong contrast and large sensing depth second harmonic image was obtained without fixation, sectioning or labelling. The three dimensional ultrastructure of porcine cornea after Nd:glass femtosecond laser intrastromal surgery was examined to evaluate the concepts of minimum-invasive all-optical refractive eye surgery. No thermal damages were recognized and the surgical outcome appeared highly predictable. Due to the similarities between the physical principals of nonlinear laser scanning microscopy and femtosecond laser ablations, a setup of the Nd:glass femtosecond laser system integrating both the surgery and probing functions was proposed.

Diode pumped Nd:glass all-solid-state femtosecond laser is promising for next generation refractive surgery, with the advantages of excellent surgical precision, minimal tissue damage and improved system stability and compactness. The microscopic evaluation of the outcome of femtosecond laser surgery is crucial before clinical applications. By two-photon laser scanning microscopy and non-invasive second harmonic imaging, the three dimensional ultrastructure of the porcine cornea is visualized without requiring slicing or staining. The minimal-invasive corneal flap cutting and non-invasive intrastromal surgery are investigated. Femtosecond laser intrastromal surgery demonstrated high ablation precision and mimimal side effects. However, there are elongated filaments/streaks observed in the cornea stroma, most likely due to the focusing optics and self-focusing.

Refractive surgery in the pursuit of perfect vision (e.g. 20/10) requires firstly an exact measurement of abberations induced by the eye and then a sophisticated surgical approach. A recent extension of wavefront measurement techniques and adaptive optics to ophthalmology has quantitatively characterized the quality of the human eye. The next milestone towards perfect vision is developing a more efficient and precise laser scalpel and evaluating minimal-invasive laser surgery strategies. Femtosecond all-solid-state MOPA lasers based on passive modelocking and chirped pulse amplification are excellent candidates for eye surgery due to their stability, ultra-high intensity and compact tabletop size. Furthermore, taking into account the peak emission in the near IR and diffraction limited focusing abilities, surgical laser systems performing precise intrastromal incisions for corneal flap resection and intrastromal corneal reshaping promise significant improvement over today's Photorefractive Keratectomy (PRK) and Laser Assisted In Situ Keratomileusis (LASIK) techniques which utilize UV excimer lasers. Through dispersion control and optimized regenerative amplification, a compact femtosecond all-solid-state laser with pulsed energy well above LIOB threshold and kHz repetition rate is constructed. After applying a pulse sequence to the eye, the modified corneal morphology is investigated by high resolution microscopy (Multi Photon/SHG Confocal Microscope).

We investigated refractive corneal surgery in vivo and in vitro by intrastromal photodisruption using a compact ultrafast femtosecond laser system. Ultrashort-pulsed lasers operating in the femtosecond time regime are associated with significantly smaller and deterministic threshold energies for photodisruption, as well as reduced shock waves and smaller cavitation bubbles than the nanosecond or picosecond lasers. Our reliable all-solid-state laser system was specifically designed for real world medical applications. By scanning the 5 micron focus spot of the laser below the corneal surface, the overlapping small ablation volumes of single pulses resulted in contiguous tissue cutting and vaporization. Pulse energies were typically in the order of a few microjoules. Combination of different scanning patterns enabled us to perform corneal flap cutting, femtosecond-LASIK, and femtosecond intrastromal keratectomy in porcine, rabbit, and primate eyes. The cuts proved to be highly precise and possessed superior dissection and surface quality. Preliminary studies show consistent refractive changes in the in vivo studies. We conclude that the technology is capable to perform a variety of corneal refractive procedures at high precision, offering advantages over current mechanical and laser devices and enabling entirely new approaches for refractive surgery.

The phase retardation of light induced by the birefringent parts of the human retina in vivo is measured with an electro-optical ellipsometer using the principle of confocal imaging. A scanning unit allows to examine an area of 25 degrees by 12.5 degrees on the retina with a resolution of 256 by 128 points with both, incident and exit beam transmitting the cornea at a fixed position. Due to this fixed beam position the Muellermatrix of the cornea can be calculated using light which is specularly reflected on blood vessels lying above the nerve fiber layer of the retina. The obtained images show a homogenous radial distribution of the retinal retardation around the fovea without the appearance of the so called Haidinger brushes. The areas with the thickest nerve fiber layers, the arcuate bundles, appear in their typical arc and were measured quantitatively. In addition, an alternative method for the compensation of corneal birefringence is evaluated by focusing the light beam onto the surface of the lens. Hereby, the measured area in the center of the cornea is 3 X 0.75 mm2.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The dependence of the fluence at the threshold of laser- induced optical breakdown on the laser pulse duration has been investigated experimentally and theoretically for human cornea, human enamel, and bovine brain tissue. For the experiments in the range from 100 fs to 200 ps, we used a femtosecond dye laser system and a picosecond Nd:YLF laser system. We observed a significant decrease of the fluence at the threshold when reducing the pulse duration. The measured dependence on the pulse duration is in good agrement with our model.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three nonlinear (beta) -barium borate (BBO) crystals were used to generate the fourth and fifth harmonic of a Nd:YLF picosecond laser with a fundamental wavelength of 1053 nm. The UV laser pulses were used to study the surface ablation of bovine soft tissue. Whereas the general study was concentrated on brain tissue, first results were also obtained with cornea tissue. The ablation efficiency as a function of pulse energy and the ablation threshold were determined for both UV wavelengths. Histology and SEM- microscopy of the performed laser lesions are presented. Furthermore, time-resolved flash photographs we recorded by illuminating the ablation area with green picosecond laser pulses and detecting the probe beam with a CCD chip. The photographs yielded information about the physical properties of the ablation process. The emission of a shock wave into the air environment as well as the ejection of dissected ablation fragments was observed for pulse energies down to 10 (mu) J. Both UV wavelengths can be combined with an ophthalmic application system, which comprises an xyz- scanning unit for realizing precalculated ablation patterns and a z-tracker for detecting the current surface position of the cornea. The information of the z-tracker can be used to compensate the axial eye-movement with the xyz-scanning unit.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Plasma mediated ablations of calf brain tissue and corneal tissue have been performed with ultrashort pulses provided by different laser systems: A 30 ps Nd:YLF amplified laser with up to 1.5 mJ of pulse energy and a powerful 180 fs Ti:Sapphire oscillator/regenerative amplifier laser system capable of pulse energies of up to 300 (mu) J. With the femtosecond pulses the threshold in energy density needed for initiating the ablation process was found to be significantly lower than with longer pulse durations. Furthermore, the amount of ablated material is by a factor of two greater with the femtosecond pulses compared to the results obtained with the picosecond pulses. Histological examinations did not show any thermal or structural damage in adjacent tissue with pulses in the pico- and femtosecond range as it could be found after irradiation with longer pulses. The morphology of the excisions is of a very high quality.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In-vitro ablation experiments of calf brain tissue with ultrashort lasers are reported. Excisions have been performed by the mechanism of plasma-mediated ablation with focused picosecond laser pulses. Results achieved with a 35 ps oscillator/regenerative amplifier Nd:YLF laser at 1053 nm and its second and fourth harmonic at 526 and 263 nm, respectively, are presented. Preliminary experiments with 19 ps laser pulses at wavelengths near 3 micrometers generated by optical parametric amplification are reported. Here, during the ablation with low photon energies no plasma was induced. Furthermore, the spectrum of laser-induced plasma sparks on the surface of fresh calf brain tissue was recorded. Atomic line widths were measured and used to determine the electron density of the plasma. With energy densities of about 100 J/cm2 values between 2 (DOT) 1017 and 5 (DOT) 1018 cm-3 were found.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new method for the fast measurement of the Z—transferfunction in the Fovea Centralis of the human eyeusing a confocal laser scanning device is presented. The tested eye is illuminated by a collimated helium—neonlaser beam and therefore focuses the light onto the retina. Reflected light is detected using confocal techniques, i.e. a pinhole in the detection unit assures that only light originating from the focal plane is sampled. Thefocus of the laser beam is scanned in one dimension along the visual axis of the eye through the retina by adding a slide defocus to the incoming beam. The Z—transferfunction can be obtained directly by measuringthe intensity of the reflected light for different focal planes. A fixation target is offered to the eye at infinity tostabilize the accommodation as well as the direct viewing. Different pinholes in the detection unit are testedto investigate signal to noise ratio and depth resolution. Furthermore, the wave aberrations of the tested eyesand the laser scanning system itself are measured using a Hartmann—Shack wavefront sensor. Once the waveaberrations are known the intensity distribution in the plane of the detection pinhole can be calculated usingdiffraction theory. Thus, the intensity which passes through a pinhole of a certain diameter on the optical axisof the system can be obtained and the Z—transferfunction can be simulated. A comparison of the measuredand simulated Z—transferfunctions for different sizes of the detection pinhole has been performed and showssubstantial similarity.

Changes in parapapillary retina height may be an early indicator of glaucomatous tissue damage. The subject of this study is the development of an automatic computer analysis for the height variations of the parapapillary retina obtained from simultaneously taken pairs of stereophotographs of optic nerve heads. The exact evaluation of stereo photographs is, so far, processed manually in the USA (Takamoto, Boston) in a timeconsuming procedure. An automatic analysis can be considered as an essential improvement in glaucoma diagnosis.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Glaucomatous diseases are one of the main reasons for blindness in modern indu- stry nations. In its chronical form this disease leads to a reduction of the nerve fi-ber layer of the retina. Therefore it is a point of interest to measure the thickness of the nerve fiber layer in the human eye in vivo. Because of the birefringent abili- ties of the nerve fiber layer an ellipsometric method can be used to measure its thickness. The next sections will describe a method based on standard ellipsometry, but using electro-optical devices instead of mechanical ones to measure the nerve fiber layer thickness faster and with less errors then it is done by mechanical ellip- sometry. 1. Introduction An eye disease that is relatively wide spreaded in modern industry nations is the chronic Glaucoma that is caused by an abnormal high eye pressure. The average va- lue for the eye pressure lies by about 20 mbar and fluctuates about S mbar during the day. Glaucomatous diseases decrease the blood flow through the retina and da

The effect of different wavelengths on corneal tissue ablation has been studied using the 1st, 2nd, and 4th harmonics of a picosecond Nd:YLF laser system. This laser system consists of an actively mode locked Nd:YLF oscillator generating 30 ps pulses and a regenerative amplifier. The laser beam was focussed onto fresh human donor or calf corneas. The corneas could be moved in 3D patterns using computer controlled stepping motors. The amount of the ablated tissue and the quality of the resulting surfaces were judged by light and scanning electron microscopy. The histology showed that the ablation depths of the IR and green laser pulses are very similar at a given energy density. SEMs revealed that UV light causes a denser packaging of the underlying collagen fibers, similar to the pseudo Bowman's membrane generated with excimer lasers. Further studies are planned concerning the investigation of the 5th harmonic at 211 nm.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three different laser systems have been investigated according to their possible application in dentistry: a free running and a Q-switched microsecond Ho:YAG laser, a free running microsecond Er:YAG laser and picosecond Nd:YLF laser system consisting of an actively mode locked oscillator and a regenerative amplifier. The experiments focused on the question if lasers can support or maybe replace ordinary drilling machines. For this purpose several cavities were generated with the lasers mentioned above. Their depth and quality were judged by light and electron microscopy. The results of the experiments showed that the picosecond Nd:YLF laser system has advantages compared to other lasers regarding their application in dentistry.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An intelligent surgical laser system, which can help the ophthalmologist to achieve higher precision and control during their procedures, has been developed by ISL as model CLS 4001. In addition to the laser and laser delivery system, the system is also equipped with a vision system (IPU), robotics motion control (MCU), and a tracking closed loop system (ETS) that tracks the eye in three dimensions (X, Y and Z). The initial patient setup is computer controlled with guidance from the vision system. The tracking system is automatically engaged when the target is in position. A multi-level tracking system is developed by integrating our vision and tracking systems which have been able to maintain our laser beam precisely on target. The capabilities of the automatic eye setup and the tracking in three dimensions provides for improved accuracy and measurement repeatability. The system is operated through the Surgical Control Unit (SCU). The SCU communicates with the IPU and the MCU through both ethernet and RS232. Various scanning pattern (i.e., line, curve, circle, spiral, etc.) can be selected with given parameters. When a warning is activated, a voice message is played that will normally require a panel touch acknowledgement. The reliability of the system is ensured in three levels: (1) hardware, (2) software real time monitoring, and (3) user. The system is currently under clinical validation.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper an extension of the principle of the Hartmann-Shack wavefront sensor to the neasureirtent of the sphericity of a specular reflection surface is presented. The features of this widely usable system are discussed by means of the application of this approach to the modeling of surface aberrations of the cornea of the eye. The results of measurements performed with a first prototype on a set of stainless steel calibration spheres of different radii are shown.

This paper presents the measurement of the wave aberrations of human eyes with a Hartmann-Shack Sensor (HSS), used in a system for active optical depth resolution improvement of the Laser Tomographic Scanner(LTS). A least-squares algorithm of modal wavefront estimation from the tested derivatives is described. The noise propagation of this algorithm is examined. And the experimental results of tested living eyes are presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

For real-time analysis of light microscopic images by using structural features we have developed a special image processing system. The major components of the system are a parallel multi--microprocessor system, an image buffer, a stepping motor driver module for x-, y-, and z-movement of the microscope, a video processing module and a binary image module. The two latter modules are special hardware to generate structural parameters of the video image in real-time. The parameters are derived from the number and optical density of individual objects within each image line. An object is recognized if its optical density exceeds a predefined threshold and its size falls into a programmable interval. We have applied this system to objectively evaluate histological changes occuring in neoplasias treated preoperatively with chemotherapy. The result is an automated mapping of residual tumor lesions for each specimen. These maps are used to define chemotherapy effects. It should be emphasized that because of its flexibility, the system described can be used more generally to analyse structures of histological images.

A microprocessor controlled photo-thermoplastic device has been developed for the real-time recording of holographic filters in a hybrid digital-optical data processing system. It is possible to position the filters with an accuracy of 0,2 µm.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In adaptive optics, the compensating phase distribution can be generated by an expansion of the turbulence phase distortions into modes of a set of basis functions, i.e. Zernike-polynomials and Karhunen-Loeve-functions. By applying a modal control concept to a practical adaptive optical system, the electrodes of a membrane mirror can be controlled in parallel with greatly reduced cross-talk. The coefficients of the approximating functions, each of which corresponds to a certain mode of the mirror surface, are fed back to the actuators by a modal control matrix. The atmospheric turbulences are taken into account by extending the local differential operator in an "observer"-like structure.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

With optically generated component filters a binary recognition of 2-D objects is possible. The correlation signals of the filters are processed by a digital computer system to achieve a classification by signal intensity and shape. The computer also controlls the filtergeneration and carries out the recognition.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Light propagation through the atmosphere is disturbed by atmospheric turbulence. This limits the high angular resolution in astronomical imaging. Active optics is a method to overcome this problem. It allows a real-time optimization of the resolving power. An active mirror was developed which consists of an electrostatically deformable membrane. The polymer foil is actuated by an electrode array with 63 hexagonal elements arranged in a ring structure. The sensitivity is 0,05 microns per volt. It works up to 4 kHz without resonances. The maximum local tilt of the membrane is 3 microns per 5 millimeter. For an atmospheric tilt compensation of the wavefront the mirror housing is in a gimbal mount. Piezo-electric actuators provide a total mirror angular movement up to 20 Hz and angular sensitivity of 77 arcsecs per kV. With this active mirror device and a multi-microprocessor control unit the stabilisation of the star-speckle pattern positions and the deconvolution of the speckle patterns are possible. Two control methods are in development and analyzed in comparison. One is working with a modified shearing interferometer as a wave-front sensor and a feedback with cross-talk compensation. The other is sensing the optical information in the image plane by a diode-array and computing the wave-front from its Fourier modulus. The compensating phase distribution is generated by an expansion of the turbulence phase distortions into modes of a set of basis functions, i.e. Zernike-polynomials and Karhunen-Loeve-functions. By applying a modal control concept to the adaptive optical system, the electrodes of a membrane mirror are controlled in parallel with compensated cross-talk. The coefficients of the approximating functions, each of which corresponds to a mode on the mirror surface, are fed back to the actuators by a modal control matrix. The system presented in this paper is designed for the 0,75 m RC-telescope with alt-az mount at the Landessternwarte in Heidelberg, F.R.G..© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.