Ophthalmic diagnosis through measurements of ocular tissues autofluorescence has recently reached its first clinical maturity. This technique is intrinsically non-invasive and, thanks to the availability of a new family of measuring instruments, is becoming reliable even if performed in a few seconds and is of no burden to the patient. Diagnostic methods based on ocular tissue autofluorescence could become important tools in the prevention of a number of diseases which may lead to blindness, and therefore have a great social impact. The present paper is intended to give, from one side, an update of the rationale concerning fluorophores in the eye and their absorption and fluorescence properties; from the other, it offers an overview of ophthalmic fluorescence techniques aimed at the detection, quantitation and discrimination of ocular autofluorescing substances, highlighting their usefulness as a diagnostic aid in the early detection and prevention of ocular diseases.

Scheimpflug slitlamp microscopy is the outstanding method to record nuclear light scattering from the crystalline lens. Until yet, calibration of measurements with this device has not been possible. In the current work, an external standard for Scheimpflug slitlamp microscopy has been developed. The standard makes it possible to calibrate measurements within a research center and between research centers. The standard consists of an artificial anterior eye chamber that is filled with an aqueous solution of polystyrene spheres. The standard is placed at a position corresponding to a measured eye in the Scheimpflug slitlamp camera. A recording is taken. The higher the concentration of the scatterer, the more light scattering is recorded. A calibration curve relating concentration of light scatterer in the phantom to units of internal gray scale in the Scheimpflug microscope, is created. The scattering of a patient lens is recorded in units of internal gray scale and transformed to concentration of standard scatterer. The developed external standard opens the possibility to make comparative measurements of nuclear lens scattering in cataract for anti cataract drug development and cataract epidemiology studies.

Hollow beam geometry in conjunction with mode-selective detection allows to realize high-sensitivity apparatuses for quasi back-scattering measurements. I present a complete theoretical analysis of the hollow beam geometry recently proposed for dynamic light scattering measurements in the human eye. The aim of the analysis is to determine the excitation and observation beam profiles at the focal plane, the volume under test and the pre-detection signal. In the analysis the concept of characteristic length of a scattering system is introduced. Using a simple formula, this parameter allows the calculation of the collection efficiency for a general beam shaping. Moreover it is extremely useful to compare the performance of different systems.

We have measured the absorption spectra of porcine and human corneas in the far ultraviolet region from 350 nm to 190 nm. The samples were sectioned from frozen corneas into thin slices of 15 micrometers to 40 micrometers in thickness. The absorption spectra shows three distinct regions from 260 nm to 190 nm: a relatively weak absorption region from 260 nm to 240 nm; a region of steep increase from 240 nm to 220 nm; and a strong and slowly increasing absorption region from 220 nm to 190 nm. The linear absorption coefficients were determined to be 2130 +/- 310 (cm^-1) at 220 nm, 2240 +/- 320 (cm^-1) at 215 nm, 2300 +/- 330 (cm^-1) at 210 nm, and 2410 +/- 370 (cm^-1) at 193 nm for porcine corneas and 2300 +/- 480 (cm^-1) at 220 nm, 2300 +/- 460 (cm^-1) at 215 nm, 2320 +/- 470 (cm^-1) at 210 nm, and 2340 +/- 450 (cm^-1) at 193 nm for human corneas. A `window of ablation' in the far ultraviolet region between 220 and 190 nm was determined. Statistical analysis was conducted to correlate the far ultraviolet absorption between the porcine and human corneas. The effect of freezing on the far ultraviolet absorption also has been studied.

We studied the effect of the temperature-dependence of the scleral absorption coefficient on the accuracy of thermal models of laser-induced scleral heating. The scleral surface temperature increase during pulsed Holmium:YAG and Thulium:YAG laser irradiation was calculated with a constant (static model) and temperature-dependent (dynamic model) absorption coefficient. The 1D heat equation was solved with the assumption that thermal diffusion during the pulse is negligible. We found that the dynamic model yields lower temperatures than the static model. For the sclera, the overestimation becomes significant when the surface temperature is above 70 degree(s)C. This study shows that the temperature-dependence of the absorption coefficient must be taken into account to accurately predict laser-induced scleral or corneal heating.

Analysis of experimental data is the evidence, that coagulation thresholds of the eye fundus with lasers irradiation, transmitted transsclerally by a monofiber with its tip compression into the sclera appeared to be lower than the thresholds of coagulation in transpuppilar methods of applications in the identical parameters of laser irradiation. Essential distinctions of the character of interaction between laser radiation and choroid in transmission of irradiation by a monofiber with compression of its tip into the sclera allowed bus to substantiate and recommend for a clinical usage the contact-compressive transscleral method of laser microsurgery, which is characterized by the following: low thresholds of coagulation of intraocular structures; wide therapeutical range of energy; low risk factor of possible complication results; simplicity of the method realization; possibility to use irradiation in all spectra range of collagen transparency.

A new very small powerful air-cooled excimer laser (193, 248, 308 nm) with metal-ceramic technology was developed by ATL Lasertechnik in Germany. The laser won 1995 Prize for the best innovation awarded by German federal states of Berlin & Brandenburg. The pulse energy of 10 - 20 mJ at high rep rates (200 - 500 Hz) from an active volume of only 1 cm³ are reached. The raw laser beam produces energy density of > 100 mJ/cm² which is comparable to the performance of standard (large) excimer lasers. Its very short pulse length (3 ns), permits extremely high peak power density (30 MW/cm²). The ATLEX SP laser uses a new type of pre-ionization technique providing high beam homogeneity at low discharge voltages. Small footprint and weight, low operation costs opens up new industrial (micro-machining) and biomedical applications. Recently the ATLEX SP laser (193 nm) has been used for corneal refractive surgery. The setup consists of splitting a 193 nm laser beam into couples of beams which simultaneously ablates the corneal surface in a symmetrical scan-like fashion. Refractive changes up to 20 diopters were realized. Results of an analysis by corneal topography showed homogeneous ablation throughout the entire ablation zone.

Preliminary results of the correction of myopia up to -7.00 D by tracked photorefractive keratectomy (T-PRK) with a scanning and tracking excimer laser by Autonomous Technologies are discussed. 41 eyes participated (20 males). 28 eyes were evaluated one month postop. At epithelization day mean uncorrected vision was 20/45.3. At one month postop, 92.8 of eyes were 20/40 and 46.4% were 20/20. No eye was worse than 20/50. 75% of eyes were within +/- 0.5 D of emmetropia and 82% were within +/- 1.00 D of emmetropia. Eyes corrected for monovision were included. One eye lost 3 lines of best corrected vision, and had more than 1.00 D induced astigmatism due to a central corneal ulcer. Additional complications included symptomatic recurrent corneal erosions which were controlled with topical hypertonic saline. T-PRK appears to allow effective correction of low to moderate myopia. Further study will establish safety and efficacy of the procedure.

Laser has been used experimentally for bonding of tissues. The probable advantages of this method are being non-contact, no foreign materials are introduce and it is fast. Previous works have shown laser welding to be an effective way for connecting blood vessels', peripheral nerves2, bowl segments3 and many other biological tissues. In ophthalmology, previous attempts to weld corneal tissue using CO2 lasers have failed4'5.

Cavitation bubbles have been shown to be a driving force of tissue cutting during pulsed laser applications in vitreoretinal surgery. Such bubbles are generated by fast overheating of water due to laser radiation absorption in either water or in tissue or due to the dielectric breakdown in the focused laser beam. An alternative approach proposed in this paper is the generation of cavitation bubbles by the fast overheating of the liquid conductive medium by a short pulse of electric current. An electrical system based on a tapered microelectrode has been developed for generation of a high voltage sub-microsecond discharge in physiological medium. The dynamics of the associated cavitation bubbles was similar to that observed with ns-pulsed fiber-delivered lasers. A highly localized zone of power dissipation--about 20 micrometers in size--resulted in a low threshold energy of cavitation bubble generation--about 3 (mu) J--in comparison to the laser-based intraocular surgical systems. The minimal distance of safe applications of this device was measured in-vitro and in-vivo as a function of energy and was compared with the ArF excimer and IR laser-based systems. The proposed device can become a convenient and a cost- effective alternative to lasers in vitreoretinal microsurgery.

We describe initial in vivo experimental results of a new hybrid digital and analog design for retinal tracking and laser beam control. An overview of the design is given. The results show in vivo tracking rates which exceed the equivalent of 38 degrees per second in the eye, with automated lesion pattern creation. Robotically-assisted laser surgery to treat conditions such as diabetic retinopathy and retinal breaks may soon be realized under clinical conditions with requisite safety using standard video hardware and inexpensive optical components based on this design.

Researchers at the USAF Academy and the University of Texas are developing a computer-assisted retinal photocoagulation system for the treatment of retinal disorders (i.e. diabetic retinopathy, retinal tears). Currently, ophthalmologists manually place therapeutic retinal lesions, an acquired technique that is tiring for both the patient and physician. The computer-assisted system under development can rapidly and safely place multiple therapeutic lesions at desired locations on the retina in a matter of seconds. Separate prototype subsystems have been developed to control lesion depth during irradiation and lesion placement to compensate for retinal movement. Both subsystems have been successfully demonstrated in vivo on pigmented rabbits using an argon continuous wave laser. Two different design approaches are being pursued to combine the capabilities of both subsystems: a digital imaging-based system and a hybrid analog-digital system. This paper will focus on progress with the digital imaging-based prototype system. A separate paper on the hybrid analog-digital system, `Hybrid Retinal Photocoagulation System', is also presented in this session.

The purpose is to assess intracorneal biocolonization of expanded polytetrafluoroethylene materials covalently coated with collagen type-I.

The knowledge of the kinetics and the density of the ejected particles can lead to a better understanding of the photoablation process. Therefore, the dynamic behavior of thermal laser ablation (initial velocity of ejected particles v₀, recoil momentum p), the ablation threshold and the particle size were studied in vitro on porcine cornea with the free-electron laser FELIX over the wavelength range 6 <EQ (lambda) <EQ 75 micrometers . The ablation cloud was made visible with a stroboscopic technique using different time delays between the (0.1 ns)- illumination pulse and FELIX. The velocity v₀ was deduced from the extension of the ablation cloud for a fluence of 2.5 J/cm² ranging from 100 - 400 n/s. Measurements of p using a pendulum lead to values between 0.7 and 5.5 mm g/s. Both values could be related to the spectroscopically determined absorption coefficient of cornea. If absorption is high (around (lambda) equals 6 and 14 - 16 micrometers ), both v₀ and p are enhanced. For the first time it has been observed that the ablation cloud differs from shot to shot, depending not only on (alpha) _cornea but also on the kind of absorber.

The purpose of this study is to investigate the healing process in cultured human cornea after infrared Free Electron Laser ablation. Fresh human cadaver cornea was ablated using the Free Electron Laser at the amide II band peak (6.45 micrometers ). The cornea was then cultured in an incubator for 18 days. Haze development within the ablated area was monitored during culture. Histologic sections of the cornea showed complete re-epithelialization of the lased area, and ablation of the underlying Bowman's layer and stroma. The endothelium appeared unaffected. Cultured human corneas may provide useful information regarding the healing process following laser ablation.

We tested the objective and subjective performance of the Holo-Or rigid gas permeable multifocal contact lens, a new trifocal diffractive contact lens. Eleven experienced and two non-experienced rigid gas permeable contact lens wearers participated in the study. Eleven patients were presbyopic (age 40 - 57) and two aphakic (age 12 and 14). All patients were tested both with their best spectacle correction for distance and near and the trifocal diffractive contact lenses. The follow up period was 3 - 8 months. Subjective opinion was also assessed. Statistical analysis was performed using Student's T-test. We did not find any significant difference in visual acuity measured at 6 m, 80 cm and 40 cm, between best spectacle correction and Holo-Or diffractive contact lenses. Depth of focus improved to a statistically significant extent when using trifocal contact lenses. A small reduction in contrast sensitivity was observed when the patients used the multifocal contact lenses. Overall satisfaction and comfort was good to excellent in ten of the thirteen patients. Two other patients who used a bifocal model of the same contact lens design showed similar results. Holo-Or trifocal diffractive contact lenses are a satisfactory means of optical correction for patients with presbyopia or accommodative problems.

The antineoplastic drug 5-fluorouracil (5-fluoro- 2,4,(1H,3H)-pyrimidinedione; 5-FU) has been used to control proliferation of penetrating fibroblasts and to prevent channel closure following glaucoma filtration surgery (trabeculectomy) or laser sclerectomy. Because of the toxicity of the drug, administration of low dosages slowly over time, at the site of the desired treatment, is indicated for optimum efficacy. Repeated injections of low dosages of the drug represent an undesirable intervention and may also result in unwanted toxicity to the corneal epithelium. A suitable biocompatible and resorbable polymer matrix composed of a poly (D,L-lactic-co-glycolic acid: PLGA) has been admixed with varying amounts of 5-FU and cast as shapes suitable for intracorneal implantation. Slow biodegradation of this polymer over a one to two week period has been shown to result in an acceptably slow drug release mechanism. An issue arising during the clinical evaluation of the efficacy of this drug delivery system was how best to quantify the concentration of 5-FU and its distribution spatially in the solid implant. FT-IR and FT-Raman spectroscopies distinguishes between the drug and the polymer matrix and were used to differentiate and quantitate the 5-FU concentration of the implants.

The effect of increased intraocular pressure (IOP) in human cadaver eyes implanted with posterior fixation keratoprosthesis was evaluated. Experiments were carried out with six fresh pairs of human cadaver eyes. One eye of each pair was implanted with a PCL-5 keratoprosthesis (8.60 mm diameter with an optic of 5.60 nm diameter) and the contralateral eye was used as a control. The keratoprosthesis was inserted through a 6 mm diameter opening trephined in the cornea. The resistance of the implanted eye to pressure on `aqueous humor' leak and/or keratoprosthesis extrusion was tested by infusing water at a constant flow of 60 mmHg/second into the anterior chamber. IOP variations were recorded with a transducer connected to a computer. IOP could be increased up to 1520 to 2324 mmHg before aqueous humor leaks occurred. Leaks were always located at the keratoprosthesis-cornea interface. No prosthesis extrusion was observed. Implanted eyes that did not leak aqueous and control eyes tore at the sclera. All posterior fixation keratoprostheses implanted eyes resisted more than 100 times the normal physiological intraocular pressure and on this standpoint is safe. Additional experiments were needed to assess the influence of suture fixation and wound healing in an animal model.

Elevation mapping corneal topography instruments provide an array of x, y, z data points describing the corneal surface. An advantage of elevation mapping instruments is their ability to calculate the 3D data array strictly from the instrument's geometry and calibration data; no assumptions about the corneal surface itself are needed. However, uncompensated eye movements can affect accuracy. Longitudinal eye movements occur along the z axis, due to pulmonary and cardiac pulsations. Eye rotations due to saccades and drifts are normal occurrences, as are translational body movements. An analysis of eye and body movements at the cornea's surface indicates a nearly linear relationship between data acquisition times of less than 33 msec, and the possible change in elevation at a point referenced to an instrument axis. The proportionality constant is expected to vary by a factor of about six over the range of clinical patients, since eye and body movements are exaggerated in juvenile patients, geriatric patients, and patients with poor vision. The analysis estimates an elevation change due to rotation and longitudinal translation of the eye of up to +/- 285 micrometers in 33 msec within the clinical population. This analysis indicates that when a topographer's acquisition time is greater than 100 microsecond(s) ec (during which an apparent elevation change of up to 1.0 micrometers may occur) testing on static objects may not provide a realistic measure of an instrument's clinical performance.

We developed novel monitoring methodology for corneal surface hydration during photorefractive keratectomy (PRK) in order to solve undercorrection issue at the central part of cornea (Central island). We employed pulsed photothermal radiometry to monitor corneal surface hydration. We performed two experiments; gelatin gel experiments and porcine cornea experiments in vitro. In the case of the gelatin gel experiments, the e-folding decay time of transient infrared radiation waveform from the ArF laser irradiated surface was prolonged from 420 microsecond(s) to 30 ms with decreasing gelatin density from 15% to 0.15%. These measured e-folding decay times were good agreements with theoretical calculations. Using porcine cornea, we observed the e-folding decay time increase during the series of ArF excimer laser irradiations. Our method may be available to know ablation efficiency change to improve the controllability of refractive correction on the PRK.

To determine if a method can be used with the Heidelberg Retinal Tomograph (HRT) to improve measurement of retinal vessel diameters. The HRT was used to acquire 3 consecutive images of the optic nerve head in 7 normal subjects to obtain a mean topographic image. The files were transferred to `CorelPHOTO-PAINT The diameters of vessels with well- defined edges were measured using the `line tool'. Each vessel diameter was measured 5 times, and an average and standard deviation were calculated. Fifty-five arterioles and 49 venules were measured from the 7 normal subjects using `CorelPHOTO-PAINT `interactivemeas' submenu. The standard deviations of the vessels ranged from 0 to 10 microns with the majority less than 5 microns in subjects using `CorelPHOTO-PAINT of the measurable vessels ranged from 2 to 17 microns with the majority greater than 5 microns. The HRT `interactivemeas' submenu permits distance measurements, but it does not enhance the image enough to clearly define the vessel edges. Enlargement and improvement of contrast reduces user error in measuring retinal vessel diameters of HRT topographic images.

Over the past years ophthalmic endoscopes with intraocular diameters as small as 0.89 mm have been developed for the observation of certain internal structures of the eye which cannot be easily visualized through conventional slit lamp/microscope arrangements. Unlike other observation systems, endoscopes feature a magnification factor that increases as their distal part nears the object to be observed. Consequently, an endoscope can also be of help as a high magnification microscope. Such an instrument has been enhanced for this purpose and is described.

Procedurally, excimer photorefractive keratectomy is based on the refractive correction of composite spherical and cylindrical ophthalmic errors of the entire eye. These refractive errors are inputted for correction at the corneal plane and for the properly controlled duration and location of laser energy. Topography is usually taken to correspondingly monitor spherical and cylindrical corneorefractive errors. While a corneal topographer provides surface morphologic information, the keratorefractive photoablation is based on the patient's spherical and cylindrical spectacle correction. Topography is at present not directly part of the procedural deterministic parameters. Examination of how corneal curvature at each of the keratometric reference loci affect the shape of the resultant corneal photoablated surface may enhance the accuracy of the desired correction. The objective of this study was to develop a methodology to utilize corneal topography for construction of models depicting pre- and post-operative keratomorphology for analysis of photorefractive keratectomy. Multiple types of models were developed then recreated in optical design software for examination of focal lengths and other optical characteristics. The corneal models were developed using data extracted from the TMS I corneal modeling system (Computed Anatomy, New York, NY). The TMS I does not allow for manipulation of data or differentiation of pre- and post-operative surfaces within its platform, thus models needed to be created for analysis. The data were imported into Matlab where 3D models, surface meshes, and contour plots were created. The data used to generate the models were pre- and post-operative curvatures, heights from the corneal apes, and x-y positions at 6400 locations on the corneal surface. Outlying non-contributory points were eliminated through statistical operations. Pre- and post- operative models were analyzed to obtain the resultant changes in the corneal surfaces during PRK. A sensitivity analysis of the corneal topography system was also performed. Ray tracings were performed using the height data and the optical design software Zemax (Focus Software, Inc., Tucson, AZ). Examining pre- and post-operative values of corneal surfaces may further the understanding of how areas of the cornea contribute toward desired visual correction. Gross resultant power across the corneal surface is used in PRK, however, understanding the contribution of each point to the average power may have important implications and prove to be significant for achieving projected surgical results.

The purpose is to calculate and compare the point-spread function and the central ablation depth (CAD) of a paraxial eye model after photo-refractive keratectomy (PRK), with single and multizone treatments. A modified Le Grand-El Hage paraxial eye model, with a pupil diameter ranging from 2 to 8 mm was used. Ray-tracing was performed for initial myopia ranging from 1 to 10D; after single zone PRK; after double zone PRK; and after tripe zone PRK. The ray-tracing of a parallel incident beam was calculated by using the paraxial matrix method. At equal CAD, the optical image quality is better after single zone treatments. Multizone treatments do not seem to be advantageous optically.

Transparency of the lens is essential to optimal visual acuity. About 90% of people above 65 years of age have some degree of lens opacity. Many of them have sufficiently dense opacities to necessitate a cataract extraction. With age the lens nucleus becomes increasingly yellow and the lens color may even become brown. Scattering within the nucleus also decreases the transparency of the lens , thereby disturbing vision (cataract) . The removal of the cataractous lens is often performed using ultrasounds (phacoemulsification) , providedthe lens is not too hard. The use of lasers can also be considered. The ability of the picosecond Nd:YLF laser is investigated with an eye model dedicated to this purpose.

In photorefractive sight correction, pre-operational computations of to-be-ablated layers are usually based on information about cornea shape that is one of the causes of aberrations. To obtain high-quality results of operation, contributions to aberrations of other origins are to be taken into account. Technique of eye-aberration mapping has been investigated, we called retina ray-tracing. It consists in directing into the eye a narrow beam, scanned (translated) in parallel to itself. Computer controls trajectory of scanning. Beam projection (spot of light) is formed on the retina. Aberrations result in varying position of the spot on retina in the course of scanning. Deviations from initial position are measured and reconstructed into wave aberration function. Mathematical relations, using Zernike polynomial expansions, were found to transform these data into necessary cornea shape correction with ablation technologies. In our experimental setup, we used the technique of acousto-optic scanning with frame time less than 10 ms for 65 sensed points. Eye-aberration mapping is realized with optical power resolution 0.1 diopter.

Trabeculectomy with early postoperative slit lamp laser suture lysis is a controlled means of maximizing bleb filtration and reducing intraocular pressure. However, this procedure is not possible in children and even some adults. Thus, an effective alternative method for postoperative laser suture lysis was investigated. Dissection of 15 scleral flaps was performed on two human cadaver eyes. Each flap was closed with two 10-0 nylon sutures and the conjunctiva repositioned to cover the sutures. Laser suture lysis was performed using an optical fiber probe for the Argon/Dye laser and a Hoskins laser lens. Five different wavelengths were studied: red (630 nm), orange (595 nm), yellow (577 nm), blue-green (488 - 514 nm), and green (514 nm). Each individual wavelength was studied using six scleral flap sutures, and a single laser application was applied to each suture. Suture lysis was attainable with each wavelength, however the argon green lysed 100 percent of the sutures. Histologic analysis demonstrated no conjunctival injury with any of the above wavelengths. These findings suggest that multiple wavelengths are effective in laser suture lysis without a slit lamp biomicroscope.

Transscleral laser (YAG:Nd, (lambda) equals 1.06 micrometers ) for ophthalmology has been developed and assembled for pulse laser transscleral treatment of eyes structures by means of adaptive optical fibers tip. `Adaptivity' means that we have used some exactly defined levels of optical fiber tip contact pressure to eyes surface to replace intertissues liquid. Such kind of fiber tip permit us apply more laser irradiation power due to decreasing of laser beam absorption in the liquid of eyes tissue. The different laser power levels, pulse duration, exposure time have been considered in correspondence with many types of adaptive fiber optical tips to optimize both transscleral coagulation and cutting process. To exactly determine the dependencies of laser irradiation spatial distributions behind sclera via contact tips pressure levels we have used as a adequate enough model He-Ne laser and eyes tissue samples. Laser system consist of power supply, control unit, laser head with cooling system, adapter for different kind of optical fibers tips. All of the above has been mounted as one case.

The possibility of increasing of human sclera transparency with the usage of 2-4-6 triiodo-benzene acid preparations water solution. Trazograph has been examined. The influence of osmotic pressure and induced histological changes in the scleral tissue was analyzed. The direct measurements of osmotic pressure of Trazograph solution and sclera were performed. Histological preparations colored hematoxylin- eosin were examined.

Corneal Ulcer is a very common disease in agricultural countries and it is responsible for 10% of the blindness causes. One of the main aspects to be observed in these cases is the increasing or decreasing of the affected area. We have been developing an automatic optical system in order to evaluate the affected area (the ulcer) to be implemented in a public hospital (400 patients per week are analyzed). The optical system is implemented in a Slit Lamp and connected to a CCD detector. The image is displayed in a PC monitor by a commercial frame grabber and a dedicated software for determining the area of the ulcer has been developed.