The means by which Argon laser trabeculoplasty (ALT) lowers intraocular pressure (IOP) is a matter of debate. Mechanical and biological laser-tissue interaction theories have been proposed. To investigate the effect laser irradiation has upon the aqueous outflow facility of trabecular meshwork (TM) cells, a suitable in-vitro model is required. Therefore the purpose of this study was to design, construct, and validate a laser irradiation and perfusion testing apparatus. The system was designed to utilize cultured TM cells seeded onto filter supports. Outflow facility will be quantified by calculating the hydraulic conductivity of the monolayer. An appropriate filter support was located, and its perfusion characteristics determined using water. Afterwards, the steady state perfusion flow rate of the filter was ascertained to be 0.096 plus or minus 0.008 ml/min when culture medium is used. Following these tests a single, baseline perfusion experiment was conducted using a TM cell monolayer. Analysis of the data produced a baseline hydraulic conductivity of 0.673 plus or minus 0.076 (mu) l/min/mm Hg/cm², well within the range found in previous reports. A dual purpose, in vitro-cellular perfusion and laser irradiation testing apparatus has been developed, tested and validates using known baseline cellular perfusion and laser irradiation testing apparatus has been developed, tested, and validated using known baseline cellular perfusion values. Future experiments will be conducted to verify these initial findings, and further experiments will be conducted using Argon laser irradiation. The response of the TM cell monolayer will then be compared to the baseline figures.

Purpose: The goal of the study is to measure the group refractive index of the human cornea in vitro to improve the accuracy of corneal thickness measurements. Methods: Corneal buttons were trephined from 23 human cadaver eyes and the group refractive index of the cornea was measured at lambda equals 840 nm using a low-coherence Michelson interferometer and the technique proposed by Sorin and Gray (Phot. Tech. Lett. 4:105 - 107, 1992). The effect of dehydration on the measurement was studied by measuring the corneal optical thickness as a function of time. Results: Preliminary measurements of the group refractive index at 840 nm gave n_g equals 1.450 plus or minus 0.024 for the human cornea, which is much higher than a calculated group refractive index of n_g equals 1.387. Because of dehydration, the optical thickness of the cornea decreased at a rate of 5.5 micrometer/minute which led to an artificially high value for the group refractive index. Conclusion: The calculated group refractive index of n_g equals 1.387 appears to be an accurate value for the purpose of corneal thickness measurements using low-coherence interferometry, and corneal group refractive index measurements can be performed in vitro if the measurements are performed rapidly to avoid the effect of dehydration.

Recently corneal autofluorescence has been proposed as an ocular diagnostic tool for diabetic retinopathy. The method is based on the sensible increase of the natural fluorescence of corneal tissue within specific wavelength in presence of early stage of diabetic retinopathy. The main advantages of this method are that the corneal autofluorescence has been demonstrated to be not age-related and that the cornea is readily accessible to be investigated. In this study 47 insulin-dependent diabetes mellitus and 51 non-insulin- dependent diabetes mellitus patients aged 20 - 90 years have been considered. Patients were selected from the Eye Clinic of S. Raffaele Hospital. The modified Airlie House classification was used to grade the diabetic retinopathy. Corneal autofluorescence has been measured by using both a specifically designed instrument and the Fluorotron Master. Corneal autofluorescence mean value for each diabetic retinopathy measured by using both the instruments correlated with the retinopathy grade.

An optical instrument for in-vivo corneal autofluorescence measurements in the human eye is described. This instrument measures corneal autofluorescence without burden to the patient. The corneal tissues are excited tangentially by wavelengths in the spectral region of 450 to 500 nm and the fluorescence emitted by the corneal tissue passing through a suitable set of barrier filters is collected by a miniature photomultiplier. Autofluorescence data are recorded in sixteen measurement cycles during a period of 10 seconds and the average value has been considered. The instrument demonstrates good safety characteristics.

Excimer Laser Corneal Shaping using an 193 nm Excimer Laser (ArF) provides a possibility for the fabrication of corneal transplants of various forms for various clinical applications such as (epi-)keratoplasty. Another area of application envisioned is the production of 'living contact lenses' for epikeratophakia. A device for lathing and perforating corneal donor tissue with a scanning laser beam is presented. A new ablation algorithm (Optimized Scanning Laser Ablation) was recently developed and increased the quality of lenticules and donor buttons considerably.

The preliminary results of hyperopic photorefractive keratectomy (HPRK) performed with the VISX-Star excimer laser on 25 eyes of 25 patients are presented. Thirteen of twenty five eyes had vision of greater than or equal to 20/40 at 1 month and 17 of 19 eyes saw greater than or equal to 20/40 3 months postoperatively. Fifteen of twenty five patients were over corrected greater than or equal to 1.00D at one month and 2 patients were overcorrected with the same amount at three months post-op. At three months, no undercorrections of greater than or equal to 1.00D were observed. At three months post-op, all eyes saw for near J5 or better. Complications included one case of induced astigmatism and one case of a loss of two lines of best corrected vision -- from 20/16 to 20/25. HPRK appears to be safe and effective in correcting hyperopia of up to 4.00D in the short term.

We have evaluated the refractive evolution in patients treated with yhyperopic PRK to assess the extent of the initial overcorrection and the time constant of regression. To this end, the time history of the refractive error (i.e. the difference between achieved and intended refractive correction) has been fitted by means of an exponential statistical model, giving information characterizing the surgical procedure with a direct clinical meaning. Both hyperopic and myopic PRk procedures have been analyzed by this method. The analysis of the fitting model parameters shows that hyperopic PRK patients exhibit a definitely higher initial overcorrection than myopic ones, and a regression time constant which is much longer. A common mechanism is proposed to be responsible for the refractive outcomes in hyperopic treatments and in myopic patients exhibiting significant central islands. The interpretation is in terms of superhydration of the central cornea, and is based on a simple physical model evaluating the amount of centripetal compression in the apical cornea.

Purpose: Establish the effects of pre-Descemetic sclero- keratectomy, a new nonpenetrating Deep-Sclerectomy filtration procedure, with and without crosslinked sodium hyaluronic acid (SKgel) implant in the rabbit animal model. Materials and Methods: Ten adult NZW rabbits had surgery only (group A) and 15 other had surgery and a crosslinked sodium hyaluronate implant inserted under the scleral flap (group B). Weekly intraocular pressure (IOP), outflow facility, and central and peripheral corneal thicknesses were measured in both the operated and the contralateral eye over a period of five months in Group A and six months in Group B. Results: IOP was consistently lower until POD 21 for Group A and POD 161 for Group B, respectively (P less than 0.05). Outflow facility was significantly higher than control eyes until POD 14 in Group A and until POD 84 in Group B. Peripheral corneal thickness returned to normal by POD 14 in Group A and POD 28 in Group B. By POD 35, there was no statistical significance between both groups in the mean of peripheral corneal thickness. Conclusion: Pre-Descemetic Sclero-Keratectomy with crosslinked sodium hyaluronate implant is effective in reducing IOP and safe operation in rabbit eyes.

Purpose: To assess keratometric changes of a new surgical refractive technique (Gel Injection Adjustable Keratoplasty or GIAK) on Eye Bank eyes. Conceived by G. Simon in 1989, GIAK consists of making a flat 360 degree intrastromal annular delamination track centered around the corneal apex and filling it with a soft gel. Methods: The track, which was made with customized helicoidal delaminators, was delaminated parallel to the corneal surface at 80% depth and was filled with a biocompatible crosslinked polyethylene oxide gel. The procedure was preformed on fresh cadaver eyes using 10 delaminators with different inner diameters (4.5, 5.0, 5.5, 6.0, 6.5, 7.0 mm) and widths (1.00 and 1.25 mm). The annular track was filled to capacity. Keratometric changes were evaluated with an automated surgical keratometer. Results: The keratometric changes induced by GIAK were between 3.4 and 11.9 diopters on average. Conclusions: This surgical technique effectively flattens the cornea and promises to be an effective technique for correction of myopia.

Purpose: The purpose of this study was to compare with computer simulations the duration, smoothness and accuracy of scanning photo-refractive keratectomy with spot diameters ranging from 0.2 to 1 mm. Methods: We calculated the number of pulses per diopter of flattening for spot sizes varying from 0.2 to 1 mm. We also computed the corneal shape after the correction of 4 diopters of myopia and 4 diopters of astigmatism with a 6 mm ablation zone and a spot size of 0.4 mm with 600 mJ/cm² peak radiant exposure and 0.8 mm with 300 mJ/cm² peak radiant exposure. The accuracy and smoothness of the ablations were compared. Results: The repetition rate required to produce corrections of myopia with a 6 mm ablation zone in a duration of 5 s per diopter is on the order of 1 kHz for spot sizes smaller than 0.5 mm, and of 100 Hz for spot sizes larger than 0.5 mm. The accuracy and smoothness after the correction of myopia and astigmatism with small and large spot sizes were not significantly different. Conclusions: This study seems to indicate that there is no theoretical advantage for using either smaller spots with higher radiant exposures or larger spots with lower radiant exposures. However, at fixed radiant exposure, treatments with smaller spots require a larger duration of surgery but provide a better accuracy for the correction of astigmatism.

Purpose: This study first evaluated the corneal ablation characteristics of (1) an Nd:YAG pumped OPO (Optical Parametric Oscillator) at 2.94 microns and (2) a short pulse Er:YAG laser. Secondly, it compared the histopathology and surface quality of these ablations with (3) a 193 nm excimer laser. Finally, the healing characteristics over 4 months of cat eyes treated with the OPO were evaluated. Methods: Custom designed Nd:YAG/OPO and Er:YAG lasers were integrated with a new scanning delivery system to perform PRK myopic correction procedures. After initial ablation studies to determine ablation thresholds and rates, human cadaver eyes and in-vivo cat eyes were treated with (1) a 6.0 mm Dia, 30 micron deep PTK ablation and (2) a 6.0 mm Dia, -5.0 Diopter PRK ablation. Cadaver eyes were also treated with a 5.0 mm Dia, -5.0 Diopter LASIK ablation. Finally, cats were treated with the OPO in a 4 month healing study. Results: Ablation thresholds below 100 mJ/cm² and ablation rates comparable to the excimer were demonstrated for both infrared systems. Light Microscopy (LM) showed no thermal damage for low fluence treatments, but noticeable thermal damage at higher fluences. SEM and TEM revealed morphologically similar surfaces for low fluence OPO and excimer samples with a smooth base and no evidence of collagen shrinkage. The Er:YAG and higher fluence OPO treated samples revealed more damage along with visible collagen coagulation and shrinkage in some cases. Healing was remarkably unremarkable. All eyes had a mild healing response with no stromal haze and showed topographic flattening. LM demonstrated nothing except a moderate increase in keratocyte activity in the upper third of the stroma. TEM confirmed this along with irregular basement membranes. Conclusions: A non- thermal ablation process called photospallation is demonstrated for the first time using short pulse infrared lasers yielding damage zones comparable to the excimer and healing which is also comparable to the excimer. Such Infrared sources are, therefore, potentially attractive competitors to the excimer to perform PRK and LASIK.

We conducted a study to determine if preserved human amniotic membrane can reduce corneal haze induced by excimer laser photoablation. Excimer photoablation was performed bilaterally on 40 New Zealand white rabbits with a 6 mm ablation zone and 120 micrometer depth (PTK) using the VISX Star. One eye was randomly covered with a preserved human amniotic membrane and secured using four interrupted 10 - 0 nylon sutures; the other eye served as control. The amniotic membranes were removed at one week, and the corneal haze was graded with a slit-lamp biomicroscopy by three masked corneal specialists (WC, KH and RF) biweekly for the ensuing 12 weeks. Histology and in situ TUNEL staining (for fragmented DNA as an index for apoptosis) was performed at days 1, 3 and 7 and at 12 weeks. One week after excimer photoablation, the amniotic membrane-covered corneas showed more anterior stromal edema, which resolved at the second week. A consistent grading of organized reticular corneal haze was noted among the three masked observers. Such corneal haze peaked at the seventh week in both groups. The amniotic membrane-covered group showed statistically significant less corneal haze (0.50 plus or minus 0.15) than the control groups (1.25 plus or minus 0.35) (p less than 0.001). The amniotic membrane-covered corneas had less inflammatory response at days 1 and 3, showing nearly nil DNA fragmentation on keratocytes on the ablated anterior stromal and less stromal fibroblast activation. There is less altered epithelial cell morphology and less epithelial hyperplasia at 1 week in these amniotic membrane-treated eyes. We concluded from this study that amniotic membrane matrix is effective in reducing corneal haze induced by excimer photoablation in rabbits and may have clinical applications.

The influence of spherical aberrations on laser-induced plasma formation in water by 6-ns Nd:YAG laser pulses of 1064 nm wavelength was investigated. Experiments and numerical calculations were carried out for focusing angles similar to those used for intraocular microsurgery. Wave form distortions of 5.5 lambda and 18.5 lambda between the optical axis and the 1/e² irradiance values of the laser beam were introduced by replacing laser achromats in the delivery system by plano- convex lenses. Aberrations of 18.5 lambda led to an increase of the energy threshold by a factor of 8.5. The threshold irradiance calculated using the diffraction limited spot size was 10 times increased as compared to the case of minimized aberrations and 48 times larger than the actual threshold. The threshold calculated with the measured focus diameter was, on the other hand, reduced by a factor of 35. This reduction is due to the presence of hot spots in the focal region of the aberrated laser beam. In these hot spots, the threshold irradiance is probably unchanged, but the threshold value is reduced when averaged over the whole measured diameter of the beam waist. The determination of breakdown threshold in the presence of aberrations leads, hence, to strongly erroneous results. In the presence of aberrations, the plasmas are up to 3 times longer and the transmitted energy is 17 - 20 times larger than without aberrations. Aberrations can thus strongly compromise the precision and safety of intraocular microsurgery where they may arise through the use of inappropriate contact lenses, tilting of the lens, and oblique light passage through the ocular media. They can further account for a major part of the differences in breakdown threshold and plasma transmission values reported in previous investigations.

Purpose: To study the healing process in cultured human corneas after Er:YAG laser ablation. Methods: Human cadaver corneas within 24 hours post mortem were ablated with a Q- switched Er:YAG laser at 2.94 micrometer wavelength. The radiant exposure was 500 mJ/cm². The cornea was cultured on a tissue supporting frame immediately after the ablation. Culture media consisted of 92% minimum essential media, 8% fetal bovine serum, 0.125% HEPES buffer solution, 0.125% gentamicin, and 0.05% fungizone. The entire tissue frame and media container were kept in an incubator at 37 degrees Celsius and 5% CO₂. Serial macroscopic photographs of the cultured corneas were taken during the healing process. Histology was performed after 30 days of culture. Results: A clear ablated crater into the stroma was observed immediately after the ablation. The thickness of thermal damage ranges between 1 and 25 micrometer. Haze development within the crater varies from the third day to the fourteenth day according to the depth and the roughness of the crater. Histologic sections of the cultured cornea showed complete re- epithelization of the lased area. Loose fibrous tissue is observed filling the ablated space beneath the epithelium. The endothelium appeared unaffected. Conclusions: The intensity and time of haze development appears dependent upon the depth of the ablation. Cultured human corneas may provide useful information regarding the healing process following laser ablation.

Laser scleral buckling (LSB) and scleral buckling are methods of inducing scleral indentation, a necessary objective in standard retinal reattachment surgery. The purpose of this study was to compare the height of scleral indentation produced by both modalities. Twenty (4 columns, 5 rows) overlapping spots of pulsed Holmium:YAG or Thulium:YAG laser were applied at the equatorial sclera in 20 human cadaver eyes (LSB group). The diameter of each laser spot was set to 2.5 mm using a custom-made laser probe. Total energy of Holmium:YAG and Thulium:YAG applied to each laser spot were 1285 mJ and 815 mJ, respectively. Scleral shrinkage and change in scleral thickness were measured. A radially oriented 5 mm silicone band was placed at the equator in 10 human cadaver eyes (explant group). The intraocular pressure (IOP) was adjusted to 4 mm Hg preoperatively, and to 16 mm Hg postoperatively in all eyes and monitored during the procedure. Scleral indentation height, assessed in frozen sections made along the eyeball equator, produced by Holmium:YAG (1.07 mm) and Thulium:YAG (1.30 mm) was less than that of explant group (3.12 mm) (p less than 0.05). Each application of a laser spot elevated the IOP by 4.9 mm Hg and the IOP decreased into a quarter of its elevation after 3.64 seconds. LSB with Thulium:YAG laser is potentially useful in retinal detachments when combined with vitrectomy for creating a shallow and broad buckling effect (i.e. in proliferative vitreoretinopathy cases).

New horizons for accurate photorefractive sight correction, afforded by novel flying spot technologies, require adequate measurements of photorefractive properties of an eye. Proposed techniques of eye refraction mapping present results of measurements for finite number of points of eye aperture, requiring to approximate these data by 3D surface. A technique of wave front approximation with Zernike polynomials is described, using optimization of the number of polynomial coefficients. Criterion of optimization is the nearest proximity of the resulted continuous surface to the values calculated for given discrete points. Methodology includes statistical evaluation of minimal root mean square deviation (RMSD) of transverse aberrations, in particular, varying consecutively the values of maximal coefficient indices of Zernike polynomials, recalculating the coefficients, and computing the value of RMSD. Optimization is finished at minimal value of RMSD. Formulas are given for computing ametropia, size of the spot of light on retina, caused by spherical aberration, coma, and astigmatism. Results are illustrated by experimental data, that could be of interest for other applications, where detailed evaluation of eye parameters is needed.

In sight correction technologies, it is of extreme importance to know what outcome of the planned operation could be. Conventionally, cornea shape is measured, or even refraction distribution in the eye, that are used for calculations of the to-be-ablated cornea layers. Unfortunately, different obstacles could arise, involving errors in these calculations. We propose another approach of measuring the to-be-inserted aberrations that would compensate for existing aberrations to get maximal sight acuity. The approach is based on measurements of wave front aberrations at the exit of an eye and iterative procedure of phase conjugation of the wave front, entering the eye. As a result of the procedure, an optimized point spread function is achieved. Shack-Hartmann sensors are used for wave front measurements, and spatial modulators -- for wave front control. Local slopes of wave front being measured, Wiener-type filtering helps to reconstruct the wave front itself. The results are reported of single-pass and double-pass modeling with experimental setup and computer simulation.

Purpose: The Er:YAG laser emitting radiation at a wavelength of 2.94 micrometer has been shown to produce precise tissue ablation because of the high water absorption at this wavelength. These studies evaluated the effects of the Er:YAG laser on pig retina utilizing a perfluoro-carbon/retina interphase with the goal to precisely ablate epiretinal membranes. Method: Various laser pulse energies were applied to the surface of pig retinas in perfluorocarbon filled enucleated eyes using a specially designed rotating sample holder. Free running ((tau) equals 250 microseconds) Er:YAG laser pulses were transmitted through a zirconium fluoride (ZrF₄) fiber guarded by a low OH-quartz fiber at its distal tip. The tip diameters measured 400 micrometers and 1 mm. The fiber probe was elevated 1 mm above the retinal surface. The laser energy was applied in a systematic fashion while alternating energy settings and probe diameters. Radiant exposures were set to 1 J/cm², 3 J/cm², 5 J/cm², and 10 J/cm². Results: Eight of ten eyes were treated with concentric circles of 3.5 mm, 6.5 mm, and 9.5 mm radius. The remaining two eyes were treated with a hand held probe. Tissue ablation increased with radiant exposure in a linear fashion. At a radiant exposure of 1 J/cm², tissue ablation was minimal with a maximum tissue ablation depth of 10 micrometers and minimal thermal damage to adjacent tissue. A radiant exposure of 10 J/cm² produced an ablation depth of 30 - 50 micrometers. As the ablation was performed under perfluorcarbon fluid, used as transmitting medium, no laser- induced pressure transients have been measured. Conclusion: The Er:YAG laser in combination with perfluorocarbon fluid produced precise and homogeneous tissue ablation of the pig retina. Such precise tissue ablation needs to be achieved in order to safely ablate epiretinal membranes in close proximity to the retina surface. Further in-vivo experiments will be done to examine the functionality of the retina after laser treatment.

Laser photocoagulation is used extensively by ophthalmologists to treat retinal disorders such as diabetic retinopathy and retinal breaks and tears. Currently, the procedure is performed manually and suffers from several drawbacks: it often requires many clinical visits, it is very tedious for both patient and physician, the laser pointing accuracy and safety margin are limited by a combination of the physician's manual dexterity and the patient's ability to hold their eye still, and there is a wide variability in retinal tissue absorption parameters. A computer-assisted hybrid system is under development that will rapidly and safely place multiple therapeutic lesions at desired locations on the retina in a matter of seconds. In the past, one of the main obstacles to such a system has been the ability to track the retina and compensate for any movement with sufficient speed during photocoagulation. Two different tracking modalities (digital image-based tracking and analog confocal tracking) were designed and tested in vivo on pigmented rabbits. These two systems are being seamlessly combined into a hybrid system which provides real-time, motion stabilized lesion placement for typical irradiation times (100 ms). This paper will detail the operation of the hybrid system and efforts toward controlling the depth of coagulation on the retinal surface.

Mid infrared lasers are considered a potential interesting approach for safer and tractionless removal of pathological tissue in vitreoretinal surgery. They include the Erbium:YAG laser emitting at 2.94 micrometers and the semiconductor diode laser at 1.93 micrometer. Due to their capability of inducing photothermal incision and ablation effects, procedures like precise tissue cutting, tissue removal and coagulation can be achieved. Examples of various steps of surgery performed with such laser sources are shown, including retinotomies, retinectomies, and removal of vitreous, epiretinal and subretinal membranes. Advantages and drawbacks of each wavelength are physically and clinically discussed in relation to the surgical procedure type (contact, noncontact), the target tissue and the absorbance of the vitreous substitute adopted (hydrated fluids, silicone oils, perfluorocarbons). According to our three years experience with these cutting lasers, it can be said that: (1) they require special knowledge and the frequent presence of a technician, (2) they surely represent a useful tool in vitreoretinal surgery, but not yet able to entirely replace conventional surgical instrumentation, (3) even if some surgical steps are better performed with such lasers, cost and complexity of use limit their effective diffusion into the clinical practice.

Continuous circular capsulorhexis (CCC) is the preferred technique for removal of the anterior capsule during cataract surgery due to this technique assuring accurate centration of the intraocular lens. During modern cataract surgery, especially with small or foldable intra ocular lenses, centration of the lens is obligatory. Radial tears at the margin of an anterior capsulotomy may be associated with the exit of at least one loop of an intraocular lens out of the capsular bag ('pea pod' effect) and its subsequent decentration. The anterior capsule is more likely to ream intact if the continuous circular capsulorhexis (CCC) technique is used. Although manual capsulorhexis is an ideal anterior capsulectomy technique for adults, many ophthalmologists are still uncomfortable with it and find it difficult to perform, especially in complicated cases such as these done behind small pupil, cataract extraction in children and pseudoexfoliation syndrome. We have developed a technique using a CO₂ laser system for safe anterior capsulotomy and tested it in animal eyes.

Two powerful techniques: quasi-elastic light scattering (QELS) and Scheimpflug imaging (SI), are combined to provide simultaneous (within a few seconds) and objective measurements of lens opacity. The sensitivity and performance of the two techniques is evaluated by inducing cold cataract in the lens of a calf eye. The QELS detects the onset of cataractogenesis much earlier while the Scheimpflug imaging system detects it much later.

The penetration of 300 nm ultraviolet radiation (UVR) in the anterior cortex of the crystalline lens was 0.45 mm, penetration being expressed as the distance attenuating the transmittance to 1/e². The estimation is based on measurement of in vivo inactivation of lactate dehydrogenase (LDH) due to in vivo exposure to UVR 300 nm. The inactivation of LDH was independent of the latency interval after the exposure within 0 - 6 h. There was a 30 - 40% inactivation of LDH in the cornea that dropped to 0% in the inner anterior cortex. The currently described method allows spatially resolved measurement of the in vivo dose of UVR 300 nm within the cornea and the crystalline lens.

Interpretation and analysis of retinal angiographic studies has been largely qualitative. Quantitative analysis of pathologic fundus features will facilitate interpretation and potentiate clinical studies where precise image metrology is vital. Fluorescein angiography studies of patients with age- related macular degeneration were digitized. Sequential temporal images were spatially-registered with polynomial warping algorithms, allowing for the construction of a three- dimensional (two spatial and one temporal) angiogram vector. Temporal profiles through spatially-registered, temporally- sequential pixels were computed. Characteristic temporal profiles for fundus background, retinal vasculature, retinal pigment epithelial atrophy, and choroidal neovascular (CNV) membranes were observed, allowing for pixel assignment and fundus feature quantitation. Segmentation and quantitation of fundus features including geographic atrophy and CNV is facilitated by spatio-temporal image analysis.

We are proposing a topographic measurement technique using a motion-less interferometer with temporal output. We suggest that its use can be extended to tomographic measurements. Thus, it can eventually replace the mechanically scanning Michelson interferometer in optical coherence tomography.

Purpose: To determine if the Heidelberg Retinal Laser Tomograph (HRT) and Flowmeter (HRF) can be modified to obtain images in supine patients. Methods: A mount was customized to securely attach the Heidelberg scanning head to an operating microscope stand. This mount was designed to allow rotation for viewing of the macula or optic nerve head region in either eye. The HRT was used to acquire 3 consecutive images of the optic nerve head in supine subjects to obtain a mean topographic image. The HRF was then used to obtain capillary flow measurements in supine subjects. Results: The optic nerve area in either the right or left eye can be safely and easily visualized with the modified Heidelberg system in supine patients for evaluation of optic nerve head topography or capillary flow. However, the configuration of the Heidelberg scanning head requires the images to be taken 180 degrees from the normal orientation of the scanning head to the patient's body. Therefore, the images are rotated 180 degrees from those taken in upright subjects. This must be considered when analyzing the data. Conclusion: The Heidelberg Retinal Tomograph and Flowmeter are capable of acquiring images in supine subjects. However, these images are rotated 180 degrees.

Corneal Ulcer is a deepithelization of the cornea and it is a very common disease in agricultural countries. The clinician most used parameter in order to identify a favorable ulcer evolution is the regress of the affected area. However, this kind of evaluation is subjective, once just the horizontal and vertical axes are measured based on a graduated scale and the affected area is estimated. Also, the registration of the disease is made by photographs. In order to overcome the subjectiveness and to register the images in a more accessible way (hard disks, floppy disks, etc.), we have developed an automatic system in order to evaluate the affected area (the ulcer). An optical system is implemented in a Slit Lamp (SL) and connected to a CCD detector. The image is displayed in PC monitor by a commercial frame grabber and a dedicated software for determining the area of the ulcer (precision of 20 mm) has been developed.

One of the optical ways to evaluate the donated cornea in order to provide a diagnostic regarding its indication for transplant is to count the number of the living endothelial cells (over 2000 cells/mm²), which are responsible for maintaining the corneal transparency. Specular Microscopes are equipments which are exclusively dedicated for this kind of evaluation. However they are of high cost and most of the Eye Banks are not provided by them. Hence, the usual evaluation is done in a Slit Lamp (SL) -- 40X magnification -- and just the aspect of the cells are subjectively observed. In order to overcome the limitations of subjective assessment and high cost, we have developed a system attached to the SL (optical system with 250X magnification image captured by a CCD detector which displays the image of the cells on a PC monitor and a dedicated software) which is able to count the endothelial cells providing a lower cost objective diagnostic of the donated cornea.

The efficiency of weak laser radiation was studied for patients having a ciliochoroidal detachment (CD). A He-Ne and diode lasers were used whose wavelength, radiating power at the lightguide face output, spot diameter, and exposition time were 0.63 micrometer, 0.05 - 01 mW, 200 micrometer, and 3 min., respectively. To study the mechanism of weak laser radiation effect with the CD, clinical and biochemical investigation techniques were exploited for seven patients before and after they had been irradiated. Hydro- and hemodynamical indices were normalized with a parallel decrease of malondialdehyde (MDA) concentration and a higher superoxide dismutase (SOD) activity in the tear fluid of the patients when the CD disappeared as a result of complex treatment employing the weak laser radiation. This proves the process of lipid peroxidation (LP) to be suppressed and the antioxidation system (AS) to become more active under the action of the weak laser radiation.

We have studied the influence of laser radiation on eye tissues. It was shown that argon laser radiation induced damages in retina and pigment epithelium. Disorganized segments of photoreceptors, dispersed vesicles were observed in retina after irradiation. The laser irradiation of pigment epithelium leads to fragmentation and dispersion of the membrane material. Changes in the protein composition of membrane proteins of retina were not observed by the method of gel-electrophoresis after laser irradiation. Electrophoresis profiles of pigment epithelium samples shown inessential changes in protein composition. The oxidation of SH-groups does not take place in these both cases either.

The Erbium:YAG laser emitting at a wavelength of 2,94 micrometer have been promised as an alternative laser for the ArF-excimer laser (193 nm) in photorefractive keratectomy (PRK). This report discusses the limitations of laser parameters such as wavelength, energy density and pulse duration for the ablation of the cornea. In addition, the melting process during ablation on the corneal surface roughness may play a role.

CWhatUC (pronounced 'see what you see') is a computer software system which will predict a patient's visual acuity using several techniques based on fundamentals of geometric optics. The scientific visualizations we propose can be clustered into two classes: retinal representations and corneal representations; however, in this paper, we focus our discussion on corneal representations. It is important to note that, for each method listed below, we can illustrate the visual acuity with or without spectacle correction. Corneal representations are meant to reveal how well the cornea focuses parallel light onto the fovea of the eye by providing a pseudo-colored display of various error metrics. These error metrics could be: (1) standard curvature representations, such as instantaneous or axial curvature, converted to refractive power maps by taking Snell's law into account; (2) the focusing distance from each refracted ray's average focus to the computed fovea; (3) the retinal distance on the retinal plane from each refracted ray to the chief ray (lateral spherical aberration). For each error metric, we show both real and simulated data, and illustrate how each representation contributes to the simulation of visual acuity.

The theoretical model of a human eye lens is presented. This model accounts effects of the spatial interaction of scatterers arising due to existence of closely packed system of particles and the complexity of refractive index of their material. The calculations of transmission and scattering spectra for a monodispersive system of scatterers were done using Monte-Carlo method. The influence of absorption on transmission spectra formation was studied.

The study of biochemical aqueous humor indices in hyphema was carried out in 5, 10, 15, 30, 45, 60 minutes after magnet- laser stimulation. The maximal increase of SOD activity has been determined in 5 minutes after stimulation. However its activity was significantly lower in 10 - 15 minutes. The second rise in SOD activity was noted in 30 minutes. On the following minutes its activity has been reduces. Catalase activity underwent wavelike changes as well as with two clearly observed ascending peaks on the 5 and 15 minutes after stimulation.

Theoretical and computer modeling approaches, such as Mie theory, radiative transfer theory, Monte Carlo simulation method were applied for tissue optics analysis in a process of its optical clearing due to refractive indices matching. CW transmittance and forward and backward scattering measurements were used for tissue structural and optical properties monitoring. As a controlled tissue samples of the human sclera were taken. As a chemical applicator-controller osmotically active trazograph solution was used. The scleral absorption and scattering spectra as well as diffusion coefficient describing the samples of the human sclera permeability to trazograph wer experimentally estimated. Presented results are general and can be applicable for description of many other fibrous tissues.

In this paper, we present our findings of the effect of the Erbium:YAG laser on cornea, trabecular meshwork, and retinal tissue. We believe the laser is a safe and effective cutting tool with tremendous potential for surgical application.

The Erbium:YAG laser may be an effective laser for use in cataract surgery. At 2.94 mm the energy is maximally absorbed by water thereby efficiently disrupting tissue with minimal surrounding thermal damage. The laser may be safer to use in the eye than conventional ultrasonic emulsifiers. Preliminary clinical studies of the safety and efficacy have begun.

The human iris possesses characteristics that make it significantly more robust for use as a biometric identifier when compared with conventional techniques such as fingerprints, face recognition or retinal scan. The iris is an overt body, thereby allowing a remote acquisition system to capture the image. Visual patterns in individual irises are highly distinctive and clearly apparent thereby minimizing the likelihood of false positives and false negatives enrollments. Such visual iris patterns are stable over time thereby requiring a single enrollment that can last over the user's lifetime. Furthermore, the digital information of the iris can be coded very effectively, requiring a modest amount of computer storage and processing. This paper describes an automated system which allows non-intrusive acquisition of quality iris images for the purposes of enrollment, verification or identification. In essence, user locale within a prescribed volume and unobtrusive gaze toward the image acquisition devices are the only engineering hardware criteria for enrollment and verification. The device operates with non- visible near infrared illumination. The initial image acquisition uses a stereo camera pair (3D vision) system to locate the subject within a relatively large operational volume. The resulting coordinates of the user's right or left eye are used to position a pan/tilt mirror and focus mechanism associated with a higher magnification camera. This camera, called the narrow field of view (NFOV) camera, is then used to acquire a high contrast fine resolution iris image which is presented to a proprietary algorithm for the generation of an 'iris code.' Finally the computed iris code is compared to a previously stored enrollment code associated with the user for verification.