Congenital or post-operative high degree astigmatism is currently corrected surgically by corneal arcuate incisions. Due to differences in manual skill in producing corneal incisions with precise depth, width, and length the final refractive results of these surgical techniques may be unpredictable. The aim of the study was to evaluate the feasibility of excimer laser in producing corneal arcuate excisions on rabbit eyes.

In order to predict corneal curvature change after intrastromal surgery three finite element models are developed and compared. The models differ essentially in the underlying assumptions about the mechanical behavior of the cornea. The first model assumes an isotropic corneal structure with a nonlinear stress/strain behavior, thus providing a lower limit for the corneal curvature change. Contrary model two assumes transverse isotropy combined with a linear stress/strain behavior, in order to provide an upper limit for corneal curvature change. Although differing in their structural assumptions, model one and two consider the cornea as being a solid structure. A third model, based on a multilayered thin shell theory, shows that this might not be sufficient. In addition the calculations are run for two different ablation patterns. The performed analyses are extremely useful in choosing ablation patterns and dimensions for intrastromal refractive surgery. But as the model predictions of corneal curvature change differ in about 4 dpt for a given pattern, more subtle modifications and a better knowledge of the mechanical parameters of the cornea are necessary in order to obtain applicability of model calculations to predict the actual outcome of a performed surgery.

A scanning pulsed beam at 213 nm creates predictable correction of myopia but the surgical procedure with the presently used laser system is not yet sufficiently safe to proceed to human clinical trials. It was found that a 70% overlap of approximate active spot size provides a refractive change as predicted 1 week after ablation. There was a minimal transient increase of IOP shortly after the ablation. There was an immediate swelling of the cornea after the ablation that gradually decreased during the following 12 weeks. The corneal epithelium did not heal until around 4 - 7 weeks after the ablation. The epithelium stained with fluorescein late after the ablation. When considerable haze was seen it decreased towards the end of the 12 weeks of observation. Approximately 30% of ablated corneas showed vessel ingrowth at 12 weeks after ablation. The 213 nm beam was obtained by frequency quintupling of the output of a Nd-Yag laser. The beam was moved with an X-Y scanner.

It was found that ablation at radiant exposures below 1 kJ/m² both for polymethylmetacrylate (PMMA) and for the human cornea is minimal. Above 1 kJ/m² the ablation rate increased approximately linearly with radiant exposure, the increase being twice as quick for cornea [0.26 (micrometers /pulse)/(kJ/m²)] as for PMMA [0.13 (micrometers /pulse)/(kJ/m²)]. Laminae of PMMA and human cornea of known thickness were ablated with nano second pulses at 213 nm. It is anticipated that the current data will serve as a basis for design of ablation procedures in the cornea.

Thirty four patients with retinochoroiditis initially treated with medical treatment and later treated with laser photocoagulation around the foci were retrospectively evaluated for the risk of recurrence of the eretinochoroiditis. We used a Kaplan-Meier representation to show the evolution of the number of patients without recurrence as a function of time and as the number of patients followed up decreases (rate of patients without recurrence at 1 year: 86 +/- 12.3% for 26 patients exposed; at 2 years: 75 +/- 16.4% for 20 patients exposed; at 3 years and at 4 years 70 +/- 17% for 17 patients exposed). The recurrence rates were compared to the data previously published in the literature. We failed to demonstrate the efficacy of laser photocoagulation on inactive retinochoroiditis for prevention of recurrence of ocular toxoplasmosis. However, the heterogeneity of our series, the great amount of patients lost to follow up, and the heterogeneity of the recurrence rates of the literature contribute to explain that result.

Orthoptic treatment for exotropia applying spheroprismatic correction and low-energy helium- neon laser stimulation possesses a series of advantages to the surgical treatment. Prismatic correction has been already applied for exotropia earlier and has proven to be quite effective treating the disease and its minor complications. But in more severe cases when exotropia is accompanied by hyperphoria exceeding 3 pr Dptr and cyclotropia, prismatic correction method is not helpful enough. To cure the most complicated cases of exotropia low-energy helium- neon laser was successfully used for the first time as the only means capable of eliminating hypertropia and cyclotropia. The novelty and high efficiency of the method enables ophthalmologists to approach concomitant squint not as an eye muscular deterioration but as physiological reaction of the visual analyzer to suppress diplopia. Thus the method eliminates the cause of squint.

A Holmium:YAG (Ho:YAG) laser assisted vitrectomy system has been developed. In vitro studies on porcine cadaver eyes were performed to determine optimal laser settings taking into account mechanical effects such as bubble formation and collapse and tissue displacements. Optimal laser settings were 60 - 80 mJ at a pulse length of 150 microsecond(s) . Measurements of induced shockwaves and associated effects led to the construction of a specially designed laser vitrectomy endoprobe that incorporates the distal end of a flexible fiber with 365 micrometers core diameter. Intraocular membranes and strands in the vitreous body of five rabbits were induced by injection of mouse fibroblasts. An additional five rabbits without alterations were treated as a control group. Cutting of membranes was possible and efficient at distances larger than 1.5 mm from the retina. Smaller distances partly led to injuries like retinal holes or ruptures that were induced by mechanical effects of the radiation.

The cloudy cornea in primary infantile glaucoma may contraindicate a goniotomy if a view of the anterior chamber angle is not obtainable through the operating microscope. The purpose of this study was to determine if a gradient-index (GRIN) endoscope was capable of improving the imaging of the anterior chamber angle structures in vitro. The anterior chambers of cadaver porcine eyes were deepened with a viscoelastic material. The GRIN lens endoscope entered the anterior chamber through a corneal incision near the limbus. The anterior chamber structures including the pectinate ligaments in the angle were clearly visualized on a video screen as the endoscope was advanced into the anterior chamber angle. The amount of illumination was automatically controlled. A low OH silica fiber having a core diameter of 100 microns and delivering 10 mJ of Holmium:YAG energy was inserted into the endoscope. Due to the low amount of energy, the pectinate ligaments were inconsistently cut. The specimens were examined with a dissecting microscope, fixed in formalin, and processed for light microscopy. A thin endoscope allows intraoperative examination of anterior segment structures when a cloudy cornea is present. Therefore, it may become a useful instrument for performing a goniotomy in primary infantile glaucoma when direct visualization of the anterior chamber angle is not possible with a goniotomy lens.

Intraocular tumors present special problems of diagnosis and treatment. Diagnostic methods include, in addition to systemic and ophthalmological examinations, ancillary examinations such as transillumination, fluorescein angiography, ultrasonography, radioactive phosphorus uptake test, radiology, computerized tomography, and fine-needle aspiration biopsy with cytological analyses. Previously, enucleation of the involved eye was generally accepted as management of malignant tumors. Improved therapeutic methods such as photocoagulation and better surgical techniques now provide a variety of therapeutical alternatives. This study consists of 21 cases of intraocular tumors that were managed by Argon laser photocoagulation. Four cases were intraocular metastasis and 17 cases were primitive intraocular tumors. Argon laser therapy proved to be totally ineffective for the intraocular metastasis and a very adequate therapy for the primitive tumors. Tumor extirpations (choroidal, cillary body, or iris tumors) using laser lancet proved to be more suitable than classic surgery.

The research of the retinal visual acuity (RVA) is one of the scientific methods of research of the functional state of the retina. Now it's hard to spread the active use of this method because of poor instrumental supply of this research and of needs for more information about diagnostical values in cases of different diseases of anterior and interior segments of an eye. We have just single reports about the use of retinometry in cases of eye traumas and secondary cataracts. The aim of this work is the research of the prognostical and diagnostical value of RVA in laser microsurgery of the anterior segment of an eye.

In recent years laser technology has undergone a tremendous development in the field of ophthalmology. New laser sources such as solid state (Er:YAG, Ho:YAG) and diode lasers have become available and exhibit promising characteristics in view of routine therapeutic procedures. Therapeutic effects are now attempted to be obtained inside the eye by making use of optical fibers having a plane distal end surface. Under these conditions the laser beam emitted from the fiber diverges according to the numerical aperture of the fiber (typically from 0.2 to 0.4). Because the therapeutic effect obtained depends primarily on the power density on the tissue to be treated, optical components can be utilized for refocusing the laser beam. For this purpose, small reshaping micro optics set at the distal end of the fiber have been extensively presented. So far, they have been developed to fit the diameter of endoscopic working channels, i.e., typically about 2.2 mm. However, this diameter should be further reduced for intraocular applications because standardized surgical ports are only 0.9 mm in diameter (20 gauge). After a short review of axial systems based on the refocusing of the beam transmitted from the fiber, a more extended presentation of systems capable of deflecting this beam is given. Designs have been evaluated with ray patterns, spot dimensions, and irradiance distribution. Ray patterns have been computed using ray-tracing algorithms on the basis of the Snell's law of refraction while irradiances have been derived with the 3D optical analysis program ASAP (BRO, USA). Rays were homogeneously distributed, spatially across the fiber core as well as angularly across its numerical aperture. Foci have been defined as the location where the cross-section of the beam is the smallest: all the rays are taken into account regardless of their intensity, so that no irradiation of the targeted tissue occurs outside this area.

High level mathematical models have been used for optimizing regimes of photocoagulation of choroid new growths with minimal damage of the sensitive retina. Supposed spectral range and temporal irradiation regimes have given good results in experiments and in clinics.

The features and advantages of diode laser coagulation of eye retina biotissues are established on the basis of computer simulation.

The optimal values of the parameters of a scanning system for laser corneal surgery are determined by using a computer model. The correction of myopia is simulated. The accuracy of the correction, the smoothness of the corneal surface after ablation, and the time needed for surgery are computed. With a beam diameter of 0.5 mm, an overlap of 60% to 80%, and a 5 mm diameter treatment zone, the simulated error is less than 0.1 Diopter for a correction of 6 Diopters or less; the roughness is less than 7% of the central ablation depth; the number of pulses per Diopter of correction is 2500 if the beam intensity distribution is Gaussian and 580 if the beam intensity distribution is uniform.

In natural science the degree of quantification can be considered as a distinctive mark of maturity of the corresponding field. Lasers have contributed a lot to quantitative diagnostic techniques in medicine. In this paper several quantitative laser techniques in diagnostic ophthalmology are briefly described and discussed.

Laser Doppler flowmetry (LDF) was applied to measure blood flow in discrete regions of the optic nerve head (ONHBF) and in the foveal region of the choroid (ChBF) in humans. LDF is based on the Doppler effect. For its ocular application, a diode laser beam (wavelength equals 810 nm, 60 mW at the cornea) was delivered to the eye through a fundus camera. For ONHBF the beam was directed at regions of the optic disk with no apparent individual vessels. For ChBF in the foveal region subjects were asked to look directly at the beam. Light scattered by red blood cells in the tissue volume illuminated by the incident laser beam was detected at the fundus image plane of the camera by an optical fiber. Two analysis schemes of the Doppler signal were developed: one uses commercial skin blood flowmeters, the other a NeXT station (Motorola 68040 based) computer system. Responses of ONHBF and ChBF to various physiological and pharmacological stimuli were obtained and shown to be in agreement with previously published findings. LDF is a valid technique for obtaining non- invasive, continuous and sensitive recordings of ONHBF and foveal ChBF, the latter without the need to dilate the pupil.

The dual beam scanning partial coherence interferometry technique, which was recently developed to measure the fundus profile of the human eye in vivo, is used for tomographic and topographic imaging and for the measurement of different retinal structures, e.g., the contour of the papilla and thickness profiles of retina and retinal nerve fiber layer. In case of well defined, sharp boundaries between two layers of different refractive indices, the absolute position of these retinal structures can be determined with a precision (standard deviation) of 5 micrometers . Compared to first results with this instrument, the measurement time for horizontal and vertical scans was reduced by a factor of 10. At present, the measuring time of a vertical scan over 10 degree(s) in steps of 0.5 degree(s) takes at least 20 seconds without and 80 seconds with signal averaging of 4 longitudinal scans over 1.5 mm distance. Further improvements to 5 - 20 seconds are discussed. The longitudinal resolution of this instrument is approximately 15 micrometers (full-width-half-maximum), depending on the coherence length of the light source; this is about 5 times better than previous measurements. Topographic and tomographic scans across the optic disk reveal an increase of thickness of the retinal nerve fiber layer at the inferior and superior rim of the disk, which are in good agreement with results published in the literature.

In the past few years a new technique for measuring intraocular distances has been developed, which is based on interferometry using partially coherent light beams and the Doppler principle. It has been shown that this technique is capable of measuring corneal thickness, axial eye length, and retinal thickness in human eyes in vivo with unprecedented precision. This technique has now been further extended to measure the anterior chamber depth and the thickness of the lens. A precision of 10 micrometers is obtained for both intraocular distances. This is more than one order of magnitude better than with conventional techniques.

We have evaluated acute laser retinal exposure in non-human primates using a Rodenstock scanning laser ophthalmoscope (SLO) equipped with spectral imaging laser sources at 488, 514, 633, and 780 nm. Confocal spectral imaging at each laser wavelength allowed evaluation of the image plane from deep within the retinal vascular layer to the more superficial nerve fiber layer in the presence and absence of the short wavelength absorption of the macular pigment. SLO angiography included both fluorescein and indocyanine green procedures to assess the extent of damage to the sensory retina, the retinal pigment epithelium (RPE), and the choroidal vasculature. All laser exposures in this experiment were from a Q-switched Neodymium laser source at an exposure level sufficient to produce vitreous hemorrhage. Confocal imaging of the nerve fiber layer revealed discrete optic nerve sector defects between the lesion site and the macula (retrograde degeneration) as well as between the lesion site and the optic disk (Wallerian degeneration). In multiple hemorrhagic exposures, lesions placed progressively distant from the macula or overlapping the macula formed bridging scars visible at deep retinal levels. Angiography revealed blood flow disturbance at the retina as well as at the choroidal vascular level. These data suggest that acute parafoveal laser retinal injury can involve both direct full thickness damage to the sensory and non-sensory retina and remote nerve fiber degeneration. Such injury has serious functional implications for both central and peripheral visual function.

Laser light source powers of our instrument LEPOSIA^R are minimized so that dynamic light scattering (DLS) measurements can be conducted with lowest intensity levels on human eye lenses (3.2 mW/cm²) within measurement times of 3 to 5 seconds. We describe an extension of DLS and an eye lens characterization along the optical axis (OA), revealing the molecular size ranges together with distributions found in lens regions parallel to the OA. The microstructures of various lens regions are separated by the analyzed radius distributions reflecting the visco-elastic properties of the eye lens. Detailed analysis and applied statistical categorization of results are described. The data obtained by DLS allow for an objective interpretation of opacity occurrences on molecular size range which are related to refraction anomalies. Apart from changes in color and fluorescence properties, the refractive anomalies can be assumed as the origin of the cataract. The bimodal radius distributions are characterized as a function of patient ages varying from 9 to 85 years. Our clinical study on 42 subjects proves a size decrease of the monomeric fraction with age, whereby their relative frequency of occurrence decreases. The larger polymeric radius fractions which are detected in lenses of all subjects increase with their age. An increase of protein polymer size is likely to be linked to the decrease of the (gamma) -crystallin fraction in old eye lens nuclei. Our preliminary analysis of clinical results is corresponding to the chemical gradients parallel to the OA of the lenses which are reported by O. Hockwin after examination on extracted eye lenses. The normalization of the lens densitometric data derived after Scheimpflug- photography against the protein size fraction analysis by DLS is performed. As a comparison mean between both techniques on identical eye lenses, an absorption corrected densitometry is conducted for the first time.

Until recently, surgical correction of hyperopia was subject to nearly total regression regardless of the method used. Laser thermokeratoplasty (LTK) with the holmium:YAG laser (Sunrise Technologies' Corneal Shaping System) is able to correct hyperopia in the range of + 1.0 to + 3.0 diopters. Up to eight spots with a spot size of 650 micrometers can be delivered simultaneously. According to the amount of hyperopia to be corrected, eight or sixteen spots are administered with respective pattern diameters of six or six and seven mm. The energy density used is 8.5 J/cm² per spot. Most of the regression occurs within the first month. In the 30 eyes with a follow-up of 6 months patient satisfaction rate is high and complications are minimal.