No abstract available.

Spectrally resolved white-light interferometry (SRWLI) was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. The accuracy of the technique was assessed by measurement of fused silica and water, the refractive indices of which have been measured at several different wavelengths. The dispersion of bovine and rabbit aqueous and vitreous humor was measured from 400 to 1100 nm. Also, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humor extracted from goat and rhesus monkey eyes. For the humors, the dispersion did not deviate significantly from water. In an additional experiment, the dispersion of aqueous and vitreous humor that had aged up to a month was compared to freshly harvested material. No difference was found between the fresh and aged media. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. Future refinement may allow measurement of the dispersion of cornea and lens across the entire visible and near-infrared wavelength band. The principles of white- light interferometry including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.

Laser photoablation using UV or IR lasers is known to trigger a photo acoustic event. Different target materials can be discriminated by analyzing the photoacoustic signal. In vitro measurements of NCPAS have revealed the necessity to integrate a number of variable elements (tissue hydration, fluence, laser beam diameter, distance to microphone, etc.). This study defines the parameters needed for the initiation of a self learning system for target material recognition. A UV excimer laser (λ=193 nm; Summit Technology, UV 200L) was used to ablate organic polymers (PMMA, PA, PVC), normal and porcine corneal scar tissue, and human cornea in vivo. NCPAS was performed using a microphone (up to 200 kHz) as a detector. During photoablation, the acoustic signal was analyzed by a multiport A/D IBM PC based digital oscilloscope. The data obtained were imported into a Matlab language program and analyzed. NCPAS allows the discrimination of different materials by a characteristically frequency shift of the photoacoustic signal. Detection and online material recognition using NCPAS is a step on the way to a `smart' laser control, based on an artificial neuronal network.

Dielectric Spectroscopy (DES) is a non-invasive contact technique for the measurement of specific electrical properties of biological tissue induced by an external electric field. This method can also be used for in vivo measurements. The frequency of the electric field is varied up to 500 MHz. The permittivity, the relaxation time and the specific conductivity as a function of corneal hydration (wet weight/dry weight) and temperature are measured (10 porcine corneas). Variation of tissue hydration has a minor influence on the signal. Only for low hydration was a significant variation of the signal detectable. Much more influence was found when the tissue temperature increased. Dielectric spectroscopy has the potential to detect thermally induced structural changes of the tissue. DES has also been used for tissue discrimination and the measurement of hydration. It can measure the cornea's viscoelastic properties in vivo and distinguish normal skin from melanoma.

Corneal topographers have made it possible to accurately map corneal shape. We applied this technology to model the post- refractive surgery cornea using Taylor series polynomials. Topography data was taken from 58 patient eyes with photorefractive keratectomy (PRK) or astigmatic photorefractive keratectomy (PARK). We looked at the changes the cornea underwent surgically, as well as the healing process. We compared the post-ablation cornea to the pre-ablation cornea and to the intended correction using novel topography maps. From the refractive map, we quantified the spherical aberration as areas of defocus on the cornea. From the pre-op exam to the first post-op exam, we measured 0.19±0.10 mm radius decrease in PRK and a 0.13±0.08 mm radius decrease in PARK in the areas where rays come to within two diopeters of defocus. As this change occurs within the optical zone, this corresponds to an increase in spherical aberration for both the PRK and the PARK patient. As the patient healed, we found additional decrease in radius of the zones of best vision in PRK patients, whereas we found no significant decrease in PARK patients. This corresponds to increased spherical aberration in the PRK patient.

We have developed a novel instrument for computerized corneal topography during surgery. The instrument measures a region of approximately 7 mm in diameter, providing the surgeon with precise values of power and astigmatism. The system is based on a Placido Disc projecting system, which is attached to the objective lens of the surgical microscope. The Placido Disc pattern is reflected by a 50% beam splitter attached to the body of the microscope. At the beam splitter we installed our home-made adaptor and a CCD monochromatic high resolution camera. A high quality frame grabber is installed on a PC and images are digitized at a 480x640 resolution. Algorithms based on image processing techniques were implemented for edge detection of pattern. Calibrating curves based on 4 spherical surfaces were generated and approximately 3600 points were calculated for each exam. Preliminary measurements on 10 healthy corneas were compared with the measurements made on an EyeSys Corneal Topographer. Mean deviation was 0.05 for radius of curvature, 0.24 D for power and 5 degrees for cylinder. This system, with some improvements, may be successfully used to diminish high post surgical astigmatisms in surgeries such as cataract and corneal transplant. This system could also be used to gather preoperative data in corneal topography assisted LASIK.

A low cost pupil-meter and tracking apparatus was developed. It is based in digital analysis of images of the anterior eye to measure the diameter of the eye pupil and to track the position of its geometrical center at video rate. The system consists in an array of infrared LEDs to illuminate the eye and a CCD video camera that captures the images of the pupil to be grabbed in a computer. A fast algorithm analyses the digital images (512x512 pixels) in real time (25 images per second) providing the pupil diameter and the location of the geometrical center within that temporal rate. The algorithm was implemented to run under DOS, Win 3.x or Win95 and is compatible with any frame-grabber. the reliability of the apparatus was tested in different subjects for the particular problems of measuring the pupil diameter during accommodation and tracking the eye position during fixation. Under the measuring range, the system is robust to moderate lateral and axial movements of the subject. The spatial resolution is 0.02 mm and the linearity in measuring the pupil diameter is better than 1% in the complete useful range. The apparatus was adapted to operate without interfering either the visual task or possible simultaneous measurements.

It is concluded that sunglasses shall block UVR and toxic blue light, allow transmittance of signal light and bring luminous intensity behind the filters to a comfortable level. It was found that some commercially available sunglasses, apart from one pair of photochromatic dark state lenses tested, block ultraviolet radiation (UVR) adequately. Further, it was found that it is possible to block the toxic blue radiation without interfering substantially on blue signal light perception. However, none of the sunglasses tested blocked the toxic blue light enough.

The preliminary results of hyperopic photorefractive keratectomy (HPRK) performed with the VISX-Star excimer laser on 40 eyes of 25 patients are presented. 28 of 40 eyes had vision of 20/40 at 6 months and 22 of 25 eyes saw 20/40 12 months postoperatively. Eleven of 40 patients were over corrected 1.00 D at 6 months and no patients were overcorrected with the same amount at 12 months postop. At six months, no undercorrections of 1.00 D were observed and 3 of 25 eyes were undercorrected by 1.00 D at 12 months postop. At 6 months postop, 35 of 40 eyes saw for near J5 or better, and 20 of 25 saw J5 at 12 months postop. Complications included: induced astigmatism of 1.00 D (6 of 40 eyes at 6 months and 3 of 25 eyes at 12 months), and loss of two lines of best corrected vision (4 of 40 at 6 month,s and 2 of 25 at 12 months). HPRK appears to be safe and effective in correcting hyperopia of up to 4.00 D in the short to medium term.

Purpose: To improve the applicability of the Gullstrand's eye model for retinal image evaluation and prediction of photo-refractive surgery outcome. Methods. The Gullstrand's eye model has been modified to allow for variable asphericity of all the refracting surfaces in the model. Formation of the retinal image is studied by means of numerical ray-tracing and by evaluation of modulation transfer function and point/line-spread-function. Results. By comparison of the model line-spread functions with experimental ones taken from the literature, best-fitting values of the asphericity parameters have been derived. The model visual performances are evaluated and compared with other eye models. Application of the model to photo-refractive surgery reveals that proper aspheric curvature in the mid periphery is essential to minimize spherical aberration and guarantee ultimate visual performances in the emmetropic eye, at the limit allowed by diffraction and photoreceptor density in the fovea. Conclusions: The proposed eye model can be useful in vision research as well as in practical applications like the design of ocular lenses and the design of improved algorithms for photorefactive surgery.

Topography assisted photoablation (TAP) is an important and logic step for future customized therapeutic photokeratectomy. Its goal is to reshape any irregular corneal surface in order to achieve an ideal sphere. Accuracy and reproducibility of the 2D and 3D topography data, strategies of data acquisition, data modification and transfer are essential elements. Accurate and appropriate subtraction methods for difference mapping are discussed. Furthermore, the properties and algorithms of the lasers' delivery systems, have to be taken into account. The overview paper describes and discusses some of the central elements of TAP.

We evaluated the efficacy, safety, and stability of femtosecond laser intrastromal refractive procedures in ex vivo and in vivo models. When compared with longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable, all-solid-state femtosecond laser system for all studies to demonstrate clinical practicality. Contiguous tissue effects were achieved by scanning a 5 μm focused laser spot below the corneal surface at pulse energies of approximately 2 - 4 microjoules. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratomileusis). Preliminary in vivo evaluation of intrastromal vision correction in a rabbit model revealed consistent and stable pachymetry changes, without significant inflammation or loss of corneal transparency. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.

A robust, real-time, dynamic eye tracker has been integrated with the short pulse mid-infrared laser scanning delivery system previously described. This system employs a Q- switched Nd:YAG laser pumped optical parametric oscillator operating at 2.94 micrometers. Previous ablation studies on human cadaver eyes and in-vivo cat eyes demonstrated very smooth ablations with extremely low damage levels similar to results with an excimer. A 4-month healing study with cats indicated no adverse healing effects. In order to treat human eyes, the tracker is required because the eyes move during the procedure due to both voluntary and involuntary motions such as breathing, heartbeat, drift, loss of fixation, saccades and microsaccades. Eye tracking techniques from the literature were compared. A limbus tracking system was best for this application. Temporal and spectral filtering techniques were implemented to reduce tracking errors, reject stray light, and increase signal to noise ratio. The expanded-capability system (IRVision AccuScan 2000 Laser System) has been tested in the lab on simulated eye targets, glass eyes, cadaver eyes, and live human subjects. Circular targets ranging from 10-mm to 14-mm diameter were successfully tracked. The tracker performed beyond expectations while the system performed myopic photorefractive keratectomy procedures on several legally blind human subjects.

Glaucoma results in permanent vision loss and affects the peripheral vision initially. It is presented in 22.5 million people worldwide and is the 3rd cause of blindness. Present tonometers are not ideal for intraocular pressure measurements in all eyes. Of concern, PRK and LASIK may result in lower intraocular pressure readings. A challenges now exists for the development of a tonometer which can easily compensate for corneas with many parameters to avoid a future increase in normal-tension glaucoma or glaucoma which is advanced.

Purpose: To evaluate discrepancies in Goldmann tonometer readings in eyes with varying degrees of corneal hydration and stromal amount. Methods. 6 Eye Bank eyes, donated by Florida Lion's Eye Bank, were evaluated. Each eye was affixed to a customized artificial orbit system with intraocular pressure (IOP) measured directly by a pressure transducer inserted into the vitreous and with a Goldmann tonometric readings. The eyes were dehydrated for 5-minute intervals in a 30% Dextran-BSS solution, with readings taken between each submersion. Once corneal thickness stabilized, a corneal trephination of 6mm was made. The corneal buttons were frozen and dehydrated by lyophilization and weighed. Results. Preliminary results show a possible overestimation in thicker corneas and an underestimation in thinner corneas, as previously published. Corresponding data on the weight of corneal material is provided. Further studies need to be conducted to determine statistical significance of the data. Conclusion. This study uses Eye Bank eyes with a protocol that produces results similar to previously published results. Further studies in correlating the amount of corneal stroma and discrepancies in Goldmann tonometer readings of intraocular pressure are important especially with the increasing acceptance of corneal refractive surgeries.

To help improve early detection of vascular eye diseases, a method, named Dynamic Observing Tonometry (DOT), for measuring the intra-ocular pressure (IOP) has been developed, which allows for simultaneous ophthalmoscopy and dynamic tonometry of the human eye. Material and Method. A system for the application of this method is presented, consisting of a transducer to be placed on the corneal surface and of a stand-alone base unit. The latter can be connected to a personal computer for further data processing and storage. The transducer consists of a Goldmann-type contact lens modified by implementing means for transparent pressure-measurement of IOP. A small flat membrane in the center of the lens applanates the cornea. A liquid transmits the applanation pressure from the opposite side of this membrane to a pressure sensor located outside the optical pathway. Time-dependent IOP's are transmitted telemetrically to the base unit for processing. Results. Current initial tests provide evidence for the viability of the concept and have demonstrated the performance of the system. Typical time dependent IOP measurements obtained with an experimental device are presented. Clinical trials with two prototypes are underway. Conclusion: The proposed device allows the ophthalmology to perform the ordinary slit-lamp fundus examinations combined with simultaneous dynamic tonometry. It offers for the first time easy and precise analysis of cardiac and respiratory- modulated intra-ocular pressure while directly observing the choroid and the papilla, as well as the analysis of heart rate variability and inspection of the iridocorneal angle at varying applied pressure. Moreover, dynamic observing tonometry gives easy access to examination procedures such as tonography and ophthalmodynamometry, which have been rarely performed despite their potential diagnostic value due to the complexity of experimental protocols hitherto used.

This paper describes a new method to examine the intraocular pressure (IOP) without any contact with the eye. In our new approach the IOP is determined indirectly from the acoustic properties of the eye, as the resonance frequencies of the bulbus are shifting with increasing IOP. In a first step simulations were made with the Finite Element Method to explore the correlation between the IOP and the acoustic properties of the bulbus. The results showed a significant rise of the resonance-frequencies with increasing IOP. Simultaneously a in-vitro measurement system was built comprising a modified michelson interferometer to measure the vibrations, a transducer to stimulate the eye and a controlling PC. With this system measurements were made with artificial eyes and enucleated pig eyes to prove the correlation experimentally. The eyes were stimulated both contacting the eye with a transducer by a stick and contactless with sonic waves. Several series of measurements showed a proportional constant of 1,25 Hz/mmHg in average, which can be detected easily. The standard deviation measuring different pig eyes was 4,5 mmHg. Next a in-vivo system was developed to study the acoustic behavior of the human eye in the real environment. The in-vivo system consists of a miniaturized semiconductor-laser interferometer complying laser safety requirements, an automatic positioning unit and an excitation unit to stimulate vibrations of the eye. Sub-micrometer vibrations of the eye can be measured in-vivo with this system.

No abstract available.

Many microsurgical procedures are performed on the threshold of what is humanly possible. In the particular case of retinal surgery, these limitations are manifested in both the physical and sensory domains. Physical limitations include tremor, fatigue and positional accuracy, while sensory limitations include both tactile sensation and visualization. Addressing these limitations will make surgery faster, safer, cheaper and more effective while enabling new classes of procedures to be developed. During retinal surgery, instruments are placed within the eye and observed through the pupil using a stereo operating microscope. While visualization using this method is quite good, the optical properties of the cornea, lens and vitreous prevent retinal structures smaller than approximately 10 microns in size from being seen. To view objects smaller than this, imperfections in the optical path must be corrected using either mathematics or adaptive optics, or be circumvented by placing a high-resolution endoscope next to the retina. This paper concentrates on the latter of these options by describing the use of GRIN lens endoscopy for in-vivo microscopic observation and diagnosis during retinal surgery. The GRIN lens endoscope is capable of significantly greater resolving power than the operating microscope, therefore increasing visualization during surgery and likewise permitting surgical procedures not currently possible.

Image change analysis will potentiate fundus feature quantitation in natural history and intervention studies for major blinding diseases such as age-related macular degeneration and diabetic retinopathy. Geometric and radiometric normalization of fundus images acquired at two points in time are required for accurate change detection, but existing methods are unsatisfactory for change analysis. We have developed and explored algorithms for correction of image misalignment (geometric) and inter- and intra-image brightness variation (radiometric) in order to facilitate highly accurate change detection. Thirty-five millimeter color fundus photographs were digitized at 500 to 1000 dpi. Custom-developed registration algorithms correcting for translation only; translation and rotation; translation, rotation, and scale; and polynomial based image-warping algorithms allowed for exploration of registration accuracy required for change detection. Registration accuracy beyond that offered by rigid body transformation is required for accurate change detection. Radiometric correction required shade-correction and normalization of inter-image statistical parameters. Precise geometric and radiometric normalization allows for highly accurate change detection. To our knowledge, these results are the first demonstration of the combination of geometric and radiometric normalization offering sufficient accuracy to allow for accurate fundus image change detection potentiating longitudinal study of retinal disease.

We have investigated the use of a 19-channel micromachined membrane deformable mirror (MMDM) for correcting aberrations of the eye to improve the resolution of fundus imaging. A Hartmann-Shack wavefront sensor (HSWS) and the MMDM are used to measure and correct aberrations existing in the anterior segments of the eye, respectively. Zernike polynomials are used to represent the MMDM surface shape as well as the optical wavefront shape. In order to control the MMDM, which has nonlinear and coupled responses to electrostatic controls, we have developed an adaptive control algorithm to iteratively adjust the control voltages of all channels, thus modulating the shape of the MMDM to reduce the variance of the optical wavefront measured using the HSWS. Experimental results using an artificial eye show that the adaptive system can compensate for low-order and some high- order aberrations, thereby improving the resolution of retinal images. The capability for correcting ocular aberrations is limited by the number of channels and the deflection range of the MMDM. Our new adaptive control algorithm allows effective use of the low-cost, compact MMDM, making adaptive optics a viable and practical technique for clinical high-resolution fundus cameras and other ophthalmic imaging instruments.

Purpose: In scanning photorefractive keratectomy, the corneal surface is reshaped by laser ablation with a scanning beam for the correction of myopia or astigmatism. A precise knowledge of the volume of corneal tissue removed by each laser pulse is necessary to be able to develop accurate ablation algorithms for scanning photorefractive keratectomy. The purpose of this study was to measure the ablation per pulse created on PMMA surfaces with a Q-switched frequency-quintupled Nd:YAG laser emitting at 213 nm. Methods: A frequency-quintupled Nd:YAG laser emitting at 213 nm with a pulse duration of 5 ns and a pulse energy of 1.2 to 1.5 mJ was used. The laser beam was focused on the surface of PMMA blocks and ablation craters were produced with 10, 50 and 100 pulses. The shape of the ablation craters was measured with an optical profilometer and compared with the beam profile measured with a laser beam diagnostic system. Results: The beam intensity distribution in the near-field consisted of two quasi-Gaussian peaks. The ablation craters contained two peaks. Assuming a Gaussian intensity distribution, the ablation per pulse in PMMA at 213 nm can be modeled by a parabolic function. Conclusions: Optical profilometry can be used to accurately measure the ablation per pulse and evaluate the homogeneity of the beam.

Background: The formation of evaporation bubbles and pressure waves during Erbium:YAG laser vitrectomy might cause intraocular damages. Methods: In water, the formation of the evaporation bubbles was observed by high-speed photography. The output energy of the quartz tip ranges from 5 to 50 mJ and the laser pulse duration from 50 μsec to 300 μsec. The dynamic of the evaporation bubbles were investigated for different diameters, various angles and radii of the quartz fiber tip. Furthermore, the spread out of the evaporation bubbles was observed for various geometries of the microsurgery probe. The induced stress waves were measured with a PVDF-hydrophone. Results: The evaporation bubble size increases semi-logarithmic with the pulse energy and reduces with the increase of the pulse duration. The diameter of the tip has no significant influence in the vapor bubble size. The expansion of the vapor bubble can be controlled by the geometry of the tip. The spread out of the vapor bubble can reduced by a slit geometry of the aspiration hole. The maximum pressure amplitude as found to be < 2 MPa. Conclusions: The evolution of evaporation bubbles and the induced pressure amplitudes from the microsurgery probe can be minimized for Erbium:YAG laser vitrectomy.

Transcleral photodisruption may provide a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. We achieved subsurface photodisruption in vitro without damaging overlying tissues with three techniques: (1) use of long laser wavelengths, (2) application of pressure, and (3) application of a dehydrating agent. Using 1 and 3, we were able to photodisrupt the internal surface of a full thickness block of sclera by focusing through the tissue.

Currently over 50 kinds of intraocular lenses (IOLs) are approved for patient use in the treatment of cataracts and ametropia. These lenses are manufactured from at least 2 kinds of silicones as well as several kinds of acrylic polymers including polyHEMA, Poly HOXEMA, a range of polymethacrylate and polyacrylate formulations. We sought to measure spectral transmission curves of a range of IOLS in the UV-visible and near IR spectral regions in order to better characterize their optical properties and to provide a baseline from which to assess their alteration following implantation over time. Consideration of how this may best be achieved are discussed. The variable ability of both explained IOLs and some samples from a range of manufacturers to block UV wavelengths is commented upon.

Intraocular lenses IOLs allow the vision restoration of cataract patients. However the ability of accommodation is lost after cataract surgery. Multifocal lenses show two or more foci with different refractive powers. Far and near objects can be at focus simultaneously. No additional spectacles are necessary. Bifocal lenses can be fabricated as multizone or as diffractive lenses. Diffractive multifocal lenses show in contrast to multi zone multifocal lenses no change of the brightness ratio for the far and near focus with change of the pupil diameter. Diffractive lenses show a saw tooth like microscopic shape with a geometrical height of the teeth in the order of microns. The lens was fabricated with a mold technique in a flexible silicone material. The molds have been lathed in metal with a ultra precision diamond lathe machine. For the test of the optical performance a MTF-measurement machine was constructed for multifocal lenses. With this machine the imaging quality and the intensity ratio of the two foci were measured. The optical quality of the lens turned out to be diffraction limited. At the University Hospital of Giessen, Germany a first clinical evaluation with 23 patients has been performed and proved for the high quality of the manufactured IOLs.

Purpose. To evaluate an innovative surgical technique for phaco-ersatz, a cataract surgery designed to restore accommodation. Techniques for very small capsulorhexis as well as the refilling procedure were developed. This study evaluates the feasibility and reproducibility of the surgical technique. Methods. The right eye of 8 NZW rabbits (≈ 2 Kg) were operated following the ARVO Statements for the Use of Animals in Ophthalmic and Vision Research. The surgery is begun by making a small peripheral capsulorhexis of about 1 mm using. The lens content is then removed. The lens is then refilled with a novel in situ polymerizable gel and the corneal incision is closed using one 10/0 Nylon interrupted stitch. Results. The capsulorhexis technique was succesfully performed and reproducible in all animals. The average size of the capsulorhexis opening was 1. 2 mm (±0.14). Lens material removal and refilling of the capsular bag with an in situ polymerizable material was also performed in each trial study. Conclusion. This surgical technique seemed feasible and reproducible.

Plasma breakdown generated by high power lasers is used in ophthalmic microsurgery for perforation of the various membranes. We report on ten years of clinical experiences with the ophthalmic Nd:YAG laser system operating alternatively in both Q-switched or mode-locked regimes. This option gives the surgeon a possibility to compare the effect of treatments with nanosecond or picosecond pulses. The pulse duration in the picosecond regime is 25 ps, the length of a nanosecond pulse is 4 ns and the energy is variable up to 70 mJ. In the ten year period the laser system was used for more than 10 000 treatments. From the results is possible to conclude that in clinical practice the picosecond pulses are better for the posterior capsule opacification treatment and that there are not retinal complications. The nanosecond pulses are useful for iridectomies. Our constructed Nd:YAG laser system provides the surgeons with the possibility to use different photodisruptive regimes for special indications, which can be very useful for the ophthalmologists.

Purpose: To determine if the free electron laser (FEL) energy can be delivered to a small space to perform optic nerve sheath fenestration with minimal acute nerve damage. Methods: A 530 mm hollow waveguide probe was designed. Optic nerve sheath fenestration (1.0 mm diameter) was performed in 8 rabbits using either the FEL (4 eyes, 6.45mm, 10 Hz, 2 mJ) or a knife (4 eyes). Within 2 hours following surgery, the animals were perfused with aldehyde fixative. The integrity of the optic nerve and glial response at the site of fenestration were evaluated on tissue selections with H&E, and antibodies to S100β or GFAP. Results: Surgery using the FEL probe was found to be technically superior to the knife. The glial reaction was limited to a zone adjacent to the fenestration and was similar in both the FEL and knife incisions. Conclusions: The FEL appears capable of efficiently performing an optic nerve sheath fenestration in a small space with minimal acute damage. Both the FEL and knife incisions result in a rapid glial response at the site of fenestration even when optic nerve integrity is not compromised.

Laser therapy is currently the only treatment of proven benefit for exudative age related macular degeneration and diabetic retinopathy. To guide treatment for macular diseases, investigations were initiated to permit overlay of previously-stored angiographic images and image sequences superimposed onto the real-time biomicroscopic fundus image. Prior to treatment, a set of partially overlapping fundus images is acquired and montaged in order to provide a map for subsequent tracking operations. A binocular slit-lamp biomicroscope interfaced to a CCD camera, framegrabber board, and PC permits acquisition and rendering of retinal images. Computer-vision algorithms facilitate robust tracking, registration, and near-video-rate image overlay of previously-stored retinal photographic and angiographic images onto the real-time fundus image. Laser treatment is guided in this augmented reality environment where the borders of the treatment target--for example, the boundaries of a choroidal neovascularization complex--are easily identified through overlay of angiographic information superimposed on, and registered with, the real-time fundus image. During periods of misregistration as judged by the amplitude of the tracking similarity metric, laser function is disabled, affording additional safety. Image-guided macular laser therapy should facilitate accurate targeting of treatable lesions and less unintentional retinal injury when compared with standard techniques.

It is of utmost importance to the development of the child's visual system that she perceives clear focused retinal images. Furthermore if the refractive problems are not corrected in due time amblyopia may occur--myopia and hyperopia can only cause important problems in the future when they are significantly large, however for the astigmatism (rather frequent in infants) and anisometropia the problems tend to be more stringent. The early evaluation of the visual status of human infants is thus of critical importance. Photorefraction is a convenient technique for this kind of subjects. Essentially a light beam is delivered into the eyes. It is refracted by the ocular media, strikes the retina, focusing or not, reflects off and is collected by a camera. The photorefraction setup we established using new technological breakthroughs on the fields of imaging devices, digital image processing and fiber optics, allows a fast noninvasive evaluation of children visual status (refractive errors, accommodation, strabismus, ...). Results of the visual screening of a group of risk' child descents of blinds or amblyopes will be presented.

A magnifying optical system (250-400X) attached to a Slit Lamp has been developed in order to evaluate the endothelium of donated corneas. The images from the endothelium are captured by a CCD and displayed in a PC monitor. The cost of the system is relatively low compared to the specular microscopes that are on the market for donated corneas (66% less expensive). The system offers two kinds of computer evaluation: interactive and automatic. The interactive counting of the endothelial cells provides a window of any shape and size desired by the clinician, where the cells are clicked by the mouse and the developed software estimates the number of endothelial cells in the cornea as a whole. The automatic counting of the cells is done by an image processing, where the cells are recognized by the developed software, without any interference of the clinician, and counted automatically. The most important features of this system compared to most that are on the market are: there are two ways for the clinical to count the cells and both can be used simultaneously (the automatic provides a quick counting of the cells and the interactive provides a wanted clinical interference on the result); many parts of the cornea can be evaluated and an average counting is provided (usually just the central part of the cornea is analyzed); real time image is provided instead of just a static image, which allows the clinician to have more information about the cornea such as the evaluation of the cells in the snail tracks.

A very common disease in agricultural countries is the corneal ulcer. Particularly in the public hospitals, several patients come every week presenting this kind of pathology. One of the most important features to diagnose the regression of the disease is the determination of the vanishing of the affected area. An automatic system (optical system and software), attached to a Slit Lamp, has been developed to determine automatically the area of the ulcer and to follow up its regression. The clinical procedure to isolate the ulcer is still done, but the measuring time is fast enough to not cause discomfort to the patient as the traditional evaluation does. The system has been used in the last 6 months in a hospital that has about 80 patients per week presenting corneal ulcer. The patients follow up (which is an indispensable criteria for the cure of the disease) has been improved by the system and has guaranteed the treatment success.

Many current corneal topography instruments (called videokeratographs) provide an `acuity index' based on corneal smoothness to analyze expected visual acuity. However, post-refractive surgery patients often exhibit better acuity than is predicted by such indices. One reason for this is that visual acuity may not necessarily be determined by overall corneal smoothness but rather by having some part of the cornea able to focus light coherently onto the fovea. We present a new method of representing visual acuity by measuring the wavefront aberration, using principles from both ray and wave optics. For each point P on the cornea, we measure the size of the associated coherence area whose optical path length (OPL), from a reference plane to P's focus, is within a certain tolerance of the OPL for P. We measured the topographies and vision of 62 eyes of patients who had undergone the corneal refractive surgery procedures of photorefractive keratectomy (PRK) and photorefractive astigmatic keratectomy (PARK). In addition to high contrast visual acuity, our vision tests included low contrast and low luminance to test the contribution of the PRK transition zone. We found our metric for visual acuity to be better than all other metrics at predicting the acuity of low contrast and low luminance. However, high contrast visual acuity was poorly predicted by all of the indices we studied, including our own. The indices provided by current videokeratographs sometimes fail for corneas whose shape differs from simple ellipsoidal models. This is the case with post-PRK and post-PARK refractive surgery patients. Our alternative representation that displays the coherence area of the wavefront has considerable advantages, and promises to be a better predictor of low contrast and low luminance visual acuity than current shape measures.

Experimental results on the optical properties of the human eye sclera controlled by administration of osmotically active chemicals, such as propylene glycol and glucose are presented. Administration of chemical agents induces diffusion of matter and as a result equalization of the refractive indices of collagen and ground material. Experimental study of influence of propylene glycol and glucose on reflectance and transmittance spectra of human eye sclera was performed. In vitro diffusion reflectance spectra of the whole human eye and transmittance spectra of the sclera samples were investigated. In vivo measurements were fulfilled on a rabbit eyes. The significant increase of transmittance and decrease of reflectance of human eye sclera and rabbit eye under action of osmolytic liquids was demonstrated. The matter diffusion coefficient for the scleral samples impregnated by glucose solution was estimated; the average value is 1.27x10^-5 ± 2.26x10^-6 cm²/sec. The results are general and can be used to describe many other fibrous tissues.

The action spectrum for light-induced damage to the retina results from the wavelength dependence transmission of the preretinal ocular media, wavelength dependent absorption in retinal chromophores and chromatic aberration of the eye optics. While various light/tissue interaction mechanisms have been implicated, thermal mechanisms dominate in the red and near-infrared for all exposure durations and in the visible for exposures shorter than a few seconds. A number of investigators have measured the transmission of the eye and the spectra of retinal absorbers, and thermal models based on these data predict the broad features of the action spectrum. Dose/response studies with lasers and incoherent light sources, conducted over the past 10 years mainly validate the thermal models.

The dependence of retinal damage threshold on laser spot size was examined for two pulsewidth regimes; nanosecond- duration Q-switched pulses from a doubled Nd:YAG laser and microsecond-duration pulses from a flashlamp-pumped dye laser. Threshold determinations were conducted for nominal retinal image sizes ranging from 1.5 mrad to 100 mrad of visual field, corresponding to image diameters of approximately 22 μm to 1.4 mm on the primate retina. In addition, baseline collimated-beam damage thresholds were determined for comparison to the extended source data. Together, this set of retinal damage thresholds reveals the functional dependence of threshold on spot size. The threshold dose was found to vary with the area of the image for larger image sizes. The results are compared to previously published extended source damage thresholds and to the ANSI Z136.1 laser safety standard maximum permissible exposure levels for diffuse reflections.

With the easy attainability of hand-held laser devices and burgeoning Light Emitting Diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with formalizing the effect of head and eye movements on smearing energy from a small optical source over the retina. This experiment describes target motion over the retina as a result of head and eye movements during a deliberate fixation task. Volunteers fixated, with (fettered) and without (unfettered) head and chin rest support, on an LED and laser source that subtended 0.1 minutes of arc visual angle. A dual Purkinje Eye-Tracker measured eye position during each 100-second fixation trial. The data showed a non-uniform retinal energy distribution with an elliptical footprint. The major axis was 2 times greater than the minor axis and oriented along the temporal/nasal retinal axis. The average half-maximum diameter measured along the major axis was 42 microns for the fettered and 108 microns for the unfettered condition. Although the eye is not a stable platform, the `smear' of energy over the retina from head and eye movements does not grossly affect spot size. The data suggest that the time dependent spot size correction of the current laser safety standards be more restrictive.

The confocal principle was applied to double pass method to measure the point spread function (PSF) of the human eye and an artificial eye, and to improve the ratio of signal to noise of retinal images. The double-pass PSFs of four human eyes on and off the optical axis of the eyes were measured. The off-axis double pass PSF in the human eye along vertical and horizontal direction is asymmetrical. When the subject looks left on the horizontal off axis, the PSF appears right of the optical axis of the subject eye. When the subject looks right the PSF is located left of the optical axis. The location of the PSF on the vertical off axis appears above the optical axis when the subject looks up. When the subject looks down the double pass PSF is located below the axis. The PSFs of the human eye recorded at varying off-axis angles are presented. Asymmetrical results suggest a more dynamic process in the optical system of the eye perhaps driven by the complicated outer or inner ocular structure.

Several mechanisms, dependent on the laser radiation and tissue parameters, affect laser tissue interaction. A common in vivo dose response experiment contains, for every parameter value, a few subjects, which are exposed to several doses. These experiments are commonly analyzed using probit models where for every parameter value, the measured data from all subjects are unified to be a single statistical batch. The analysis is then performed under the assumption that the batch responses are statistically independent and that they all originate from the same distribution. However, it is well known that even individuals, that have many common characteristics, may respond differently to equal drug dose or identical medical treatment. Thus, it is reasonable to assume that unaccounted subjects' dissimilarity may affect and bias the results of the statistical analysis. As a part of our study, on the stochastic characteristics of laser (ocular) tissue interactions, we reanalyzed the raw data of the U.S. Army Medical Research Detachment Walter Reed Army Institute of Research (USAMRD-WRAIR) spectral ED50's experiments. Some effects of specimen dissimilarity on the results of the experiment analysis will be presented and discussed.

Confocal scanning laser ophthalmoscopy (CSLO) combined with the high numerical aperture of the snake eye was used to evaluate laser injury at the photoreceptor and vascular retinal layers. An Argon laser source focused within a 35 micron retinal spot was used to produce a range of exposures from 152 to 1000 μjoules in the retinas of the Checkered Garter and Great Plains Rat snake. Anesthesia was induced with ketamine and xylazine. In vivo exposure sites measured post exposure showed unique photoreceptor damage characterized by surviving photoreceptors that were highly reflective and saturated, swollen and revealed more complex mode structure than normal photoreceptors when imaged under higher magnification. Evidence of oxidative stress was observed in photoreceptor cells peripheral to the lesion site as a late developing fluorescence (1-2 hour post exposure) following injection of Dichlorodihydrofluorescein diacetate, a marker of oxidative stress. At the anterior retina, acute exposure produced `sticky' blood cells, identified as leukocytes with Acridine orange. These findings indicate that laser retinal injury in large eyes, such as the human eye may involve pathophysiological cellular dynamics in both posterior and anterior retina and in normal retina adjacent to lesion sites. Photoreceptor movement outside the lesion site may relate to alterations in photoreceptor orientation and the efficiency of the photoreceptors quantal catch.

We examined acute laser exposure effects in awake task- oriented non-human primates. These animals were trained to discriminate between various acuity targets that initially exceeded 1 minute of arc. They were exposed in the fovea and parafovea by aligning the output from a laser source with the gap of threshold Landolt ring. Parafoveal exposures were produced by offsetting the laser source and Landolt ring gap by 1 degree. For small spot exposures (< 100 μm) using repetitively pulsed (20 Hz) Q-switched laser (532 nm) pulses above the retinal damage threshold, initial acuity deficits returned to pre-exposure baseline acuity within 30 minute postexposure. Periodic ophthalmoscopic examinations revealed punctate lesions within the fovea as well as parafoveal region. Off-axis exposures produced a greater abundance of parafoveal punctate lesions. With repetitive exposures over a period of 6 months to one year, immediate postexposure recoveries in visual acuity lengthened from minutes to hours and eventually the initial deficits became permanent. These results suggest that Q-switched visible laser pulses may induced photoreceptor pathology prior to the observance of significant acuity changes and/or initiation of the photochemical transduction process. If this hypothesis is correct, Q-switched laser damage may be more selective to the outer segment of the photoreceptor where the transduction mechanism presumably is resident.

Two Q-switched military accident cases involving foveal retinal damage were followed for at least two years with a variety of morphological and functional diagnostic techniques. Both cases demonstrated remarkable recovery of visual acuity and contrast sensitivity within 1 to 4 months post exposure. Early deficits in visual acuity, sine wave contrast sensitivity, various measures of color vision, and focal electrophysiological measures all showed remarkable recovery. With the use of a scanning laser ophthalmoscope (SLO), we were able to further evaluate the retinal preference threshold contrast targets and found that small targets requiring foveal resolution were initially placed superior and slightly temporal to the damaged fovea in these eyes, even though visual acuity in these eyes was 20/15 or better. In one of these cases, a return to foveal functionality was demonstrated even though the fovea appeared lightly scarred small test targets were placed at its center for detection. In the second case, the PRL stayed superior temporal. Attempts to force target resolution in this area were unsuccessful. These findings suggest a more active role of neural retinal plasticity in the damage recovery process as well as caution in assuming that all such injuries will exhibit such plasticity.

The authors report the clinical findings of a civilian patient who unintentionally looked into the laser beam of a British range finder, obtained on the black market. The patient was investigated by fluorescein angiography. Indocyanine green angiography (ICG) and microperimetry both in the acute stage (2 hours) and four weeks later. Hundred mg prednisone tapered over 9 days was prescribed. Additionally 50 μg tissue plasminogen activator (TPA) and 0.5 ml pure C₂F₆ were injected in the vitreous. In the acute phase hemorrhage was located beneath the retina, primarily beneath the retinal pigment epithelium. Retinal defects as seen initially over the subretinal blood, were reduced after four weeks, but a retinal defect ranging from the lasered site towards the fovea remained. Visual acuity slightly increased from 20/100 to 20/63. ICG showed a large hypofluorescent spot in the macula. The technical parameters of the range finder were: Nd:YAG laser (1064 nm), pulse duration 10 ns, beam divergence 1.5 mrad, energy 10 mJ. A range finder can produce severe macular injury. The primary laser tissue interaction mechanism seems to be explosive disruption of choroidal tissue. Intravitral injection of TPA and C₂F₆ may be an adjunct in the therapy of acute laser lesions. A late complication can be secondary choroidal neovascularization.

Laser accidents and incidents are an unfortunate but nevertheless critical source of information for those involved in laser safety standards, medical research and training. Laser safety standards are based on quantitative animal research as well as lessons learned from retinal injury induced by accidental human laser exposure. Laser accident case analyses provide important functional and treatment guidelines that help establish laser safety standards. The LAIR helps scientists and clinicians integrate and organize their respective contributions to laser safety and medical prognosis and treatment of laser eye injuries. This paper defines the scope and means of data collection, distribution, presentation and analysis implemented in LAIR.

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the benefit obtained from treatment and allow safe perifoveal photocoagulation. We have developed a rat model for studying the efficacy of putative neuroprotective compounds in ameliorating laser-induced retinal damage. Four compounds were evaluated: the corticosteroid methylprednisolone, the glutamate-receptor blocker MK-801, the anti-oxidant enzyme superoxide dismutase, and the calcim-overload antagonist flunarizine. The study was carried out in two steps: in the first, the histopathological development of retinal laser injuries was studied. Argon laser lesions were inflicted in the retinas of 18 pigmented rats. The animals were sacrificed after 3, 20 or 60 days and their retinal lesions were evaluated under the light microscope. The laser injury mainly involved the outer layers of the retina, where it destroyed significant numbers of photoreceptor cells. Over time, evidence of two major histopathological processes was observed: traction of adjacent nomral retinal cells into the central area of the lesion forming an internal retinal bulging, and a retinal pigmented epithelial proliferative reaction associated with subretinal neovascularization and invations of the retinal lesion site by phagocytes. The neuroprotective effects of each of the four compounds were verified in a second step of the study. For each drug tested, 12 rats were irradiated wtih argon laser inflictions: six of them received the tested agent while the other six were treated with the corresponding vehicle. Twenty days after laser expsoure, the rats were sacrificed and their lesions were subjected to image-analysis morphometry. The extent of retianl damage was assessed by measuring the lesion diameter and the amount of photoreceptor cell loss in the outer nuclear layer. Methylprednisolone and MI-801 were shown to ameliorate laser-induced retinal damage, whereas both superoxide dismutase and flunarizine were ineffective. Furthermore, MK-801 diminished the proliferative reaction of the retinal pigment epithelial cells. On the basis of our results we suggest that the pigmented rat model is suitable for studying and screening various compounds for their neuroprotective efficacy in treating retinal laser injury. We further suggest that glutamate might play a key role in mediating retinal injury induced by laser irradiation.

Purpose. To evaluate therapeutics for attenuating retinal laser injury. Methods. New Zealand Red rabbits (n=76) were pretreated (IV) with either a single dose of hydroxyethyl starch conjugated deferoxamine (HES-DFO, n=29) (6.1 ml/kg, 16.4 mg/ml) or methylprednisolone sodium succinate (MP, n=22) (30 mg/kg, followed by taper of 30, 20, 20, and 10 mg/kg/day for a total of 5d). Controls were untreated (n=25). Fifteen min later, animals were irradiated with a multiline cw argon laser (285 mW, 10 msec pulse durations, 16 lesions/eye). Funduscopy, fluorescein angiography, histology, and morphometry were performed at 10 min, 1h, 3h, 24h, 1 mo, and 6 mo after irradiation. Leukocytes were counted at lesion centers for retinal and choroidal compartments at 1, 3, and 24h. Results. At 3h, percent area incrase for the lesions was highest for MP (44%) and lowest for HES-DFO (16%)(p<0.05). In hemorrhagic lesions, MP treatment resulted in the highest increase of retinal neotrophils by 24h (p<0.05), and by 1 and 6 mo extensive chorio-retinal scarring occurred in nonhemorrhagic and hemorrhagic lesions. Also, no benefit was demonstrated on sparing of photoreceptors with MP treatment. Conclusions. Treatment of laser-induced retinal injury with methylprednisolone (MP) exacerbates acute inflammation and long-term chorio-retinal scarring; however, hydroxyethyl starch conjugated deferoxamine therapy ameliorates these aspects of injury. Data suggest caution in the use of MP therapy for laser injuries.

A color naming task using a computer controlled color monitor (p22 blue, p43 green and p22 and phosphors) was performed with various laser eye protection devices (LEPD) mounted in spectacle frames. Eight standard display colors were used, and were chosen to mimic common phosphor driven color displays. The LEPD spanned the range from out-of-band devices protecting only against infrared wavelengths to those with 532-nm in-band protection, using both dielectric stack and dye technologies. Theoretical and actual performance on the color-naming task was compared using a model. This model (lighting compatibility model: LICOM) uses the spectra of the display phosphors and the spectral transmission profiles of the LEPD to predict shifts of the display color loci in CIE space. The model predictions were compared against colorimetric readings of the monitor colors through the LEPD. These predictions further were compared to actual color naming error rates. Some Euclidean distances in CIELUV uniform color space and/or numerical changes in chromaticity predicted error rates relatively well. Better results were found by fitting color naming regions to the data and testing for boundary crossings. These regions will need to be refined into non-contiguous zones for future modeling since some colors tend to disappear entirely with specific LEPD.

Retinal vessel oxygen saturation has been suggested as a parameter for monitoring a wide range of conditions including occult blood los and a variety of ophthalmic diseases. We have developed an Eye Oximeter (EOX), that noninvasively measures the oxygen saturation of the blood in individual large retinal vessels using scanning lasers. 1D vessel extinction profiles are obtained at four wavelengths (629, 678, 821 and 899 nm), and the vessel transmittances computed. The oxygen saturation of blood within the vessel is then calculated from the transmittance data. We have performed an in vitro experiment on human blood which demonstrates the calibration of the EOX measurements and validates our oximetry equations. Retinal vessel oxygen saturation was measured in a human subject and found to be 65%O₂Sat and 101 - 102%O₂Sat in the veins and arteries on the optic disk. Irregularities in the background measured away from the optic disk resulted in a large variance in the calculated saturation when compared to measurements made on the disk.

Purpose: The goal of this presentation is to discuss the use of the Light Shaping Beam Homogenizer in an optical system for scanning-spot PRK. Methods: The basic principle of the LSBH is the transformation of any incident intensity distribution by light scattering on an irregular microlens structure z = f(x,y). The relief of this microlens structure is determined by a defined statistical function, i.e. it is defined by the mean root-squared tilt σ of the surface relief. Therefore, the beam evolution after the LSBH and in the focal plane of an imaging lens was measured for various root-squared tilts. Beside this, an optical setup for scanning-spot PRK was assembled according to the theoretical and experimental results. Results: The divergence, homogeneity and the Gaussian radius of the intensity distribution in the treatment plane of the scanning-spot PRK laser system is mainly characterized by dependent on root-mean-square tilt σ of the LSBH, as it will be explained by the theoretical description of the LSBH. Conclusions: The LSBH represents a simple, low cost beam homogenizer with low energy losses, for scanning-spot excimer laser systems.

Imaging of chorodial features is possible through an undilated pupil, and without the use of dye by employing a new device which scans a laser line over the patients fundus to form real time video images. Further adjustments allow the device to produce images having fields of view from 60 to 15 degrees in width. Additionally, diode laser sources provide illumination wavelengths of 532, 635, 670, 690, and 820 nm. The combined functions of line scanning, adjustable focus depth in the z plane, and switchable illumination wavelength produce greyscale video images which clearly show detailed features of the patients choroid. In addition, the optic nerve head geometry is shown with very high resolution.

Experimental in vitro studies of speckle-modulated laser field arising after transmission through different type of human cataractous lenses are presented. Computer analysis of digital imaging has allowed to determinate the degree of destruction of spatial coherence scattered laser beam and the angle of resolution of the retina using Retinal Analyzer of Vision (AROL-1) in diagnosis of cataract. Measurement of retinal visual acuity (RVA) in 135 patient with different types of cataract (senile, complicated, posterior capsular) before and after cataract extraction and also in vitro measurement of RVA with extracted cataractal lenses has shown that laser retinometer can be used for evaluating visual acuity within 0.3 - 1, practically for all types of cataracts.

Retinal tissue is subject to ischemia from diabetic retinopathy and other conditions that affect the retinal vasculature such as lupus erythematosus and temporal arteritis. There is evidence in animal models of reversible ischemia that a therapeutic window exists during early recovery when agents that reduce glutamate activity at its receptor sites can rescue neurons from injury. To model ischemia, we used sodium cyanide (NaCN), to inhibit oxidative metabolism, and 2-deoxyglucose (2-DG) to inhibit glycolysis. Dissociated rabbit retina cells were studied to evaluate the potential neuroprotective effects of N-acetyl-aspartyl-glutamate (MAAG), which competes with glutamate as a low-potency agonist at the NMDA receptor complex. N-acetylated α-linked acidic dipeptidase (NAALADase; the NAAG-hydrolyzing enzyme) is responsible for the hydrolysis of NAAG into glutamate, a neurotransmitter and potent excitotoxin, and N-acetylaspartate. 2-Phosphonyl-methyl pentanedioic acid (PMPA) and β-linked NAAG (β-NAAG), inhibitors of NAALADase, were also tested, since inhibition of NAALADase could reduce synaptic glutamate and increase the concentration of NAAG. We found that metabolic inhibition with NaCN/2-DG for 1 hour caused 50% toxicity as assessed with the MTT assay. Co-treatment with NAAG resulted in dose-dependent protection of up to 55% (p<0.005). When the non-hydrolyzable, NAALADase inhibitor β-NAAG was employed dose-dependent protection of up to 37% was observed (p<0.001). PMPA also showed 48% protection (p<.05-.001) against these insults. These data suggest that NAAG may antagonize the effect of glutamate at the NMDA receptor complex in retina. Inhibition of NAALADase by PMPA and β-NAAG may increase the activity of endogenous NAAG.

Purpose: We analyzed the effect of energy and rate of cutting on the in vivo ocular response to 2.94 μm wavelength Free Electron Laser incision of the cornea. We were interested in the difference between our clinical observations of the initial laser lesion and the ocular response using the biomicroscope versus optical coherence tomographs. We were also interested in the difference between these clinical in vivo data and our findings from light micrographs of fixed tissue. Methods: Corneas were incised with FEL at 2.94 μm wavelength and either 2.5 or 3.5 mJ/1.4 μsec. the rate of movement of the laser beam across tissue ranged from 0.2 mm/sec to 1.2 mm/sec. Eyes were examined for two hours postoperatively using optical coherence tomography (OCT) and compared to the clinical slit lamp examination and to light microscopic examination of fixed tissue sections. Results: OCT revealed a dramatic fibrin response directly correlated to the slow sweep of the FEL beam across the tissue (longer duration of tissue exposure to the laser beam). The OCt was better than examination at the slit lamp at demonstrating sites of fibrin attachments.

Glaucoma procedures tend to induce ocular hypotony. Seeking to determine the aqueous outflow pathway, we investigated casting the outflow network by in vivo injection of a polymer in the anterior chamber. Poly(methyl methacrylate) (PMMA) casts of cilioscleral sinus and aqueous veins were made by injecting a mixture of methyl methacrylate, initiator, promoter and blue ink, through the limbus, in the anterior chamber of a anesthetized rabbit. The transfer of PMMA from the cilioscleral sinus of the rabbit eye to the aqueous veins was shown. The anterior chamber and the cilioscleral sinus casts were colored in blue but the aqueous veins casts were transparent due to the filtering effect of the Meshwork discriminating the ink penetration in the aqueous veins. This technique will be useful to help understanding the role-played by the aqueous veins after glaucoma surgery, or after implantation of devices designed to reduce intraocular pressure.