New way for investigation of visual field, based on virtual reality methods, is presented. It can use for central and paracentral scotomas registration. The study is realized by presentation of the luminous stimuli at monitor screen and its observation with two open eyes. The liquid-crystal shutters are fixed before eyes. Special driver alternately opens that right, that left eyes with frequency exceeding frequency of flicker fusion. This enables to control visibility of vision field separate areas. Program provides stimulus presentation in accident manner in different areas of visual field, so that some of presentation coincides by phase with right eye opening, but some with left. Patient press space bar if he observe stimulus. As the result computer print two vision field maps in which stimulus is invisible by right, or by left eyes, that is to say draws scotomas. Thereby this enables to fix central scotoma borders, as well as suppression scotoma in strabismus too. In program are provided possibility to change brightness and color of stimuli, background and fixation point, time and frequency of appearance of stimulus, its dimension and shape. Modification of device is considered in stationary (on the base of personal computer) and portable variant.

To allow measurements of the intraocular pressure (IOP) by glaucoma patients themselves (self-tonometry) a handheld-interferometer system for non-contact in vivo measurements of microvibrations of the human eye was realized. The measurement principle is based on the dependence of the resonance frequencies of the human eye on the IOP. To analyze this, the human eye is stimulated by ultrasonic waves and the induced microvibrations are measured with a vibrometer and processed by a DSP unit. Beside a stabilized diode laser and a low noise photodetector an exact three-dimensional positioning system had to be developed to guarantee reliable measurements. To investigate the corresponding requirements a camera-based system for the detection of human eye movements was developed and test series with several persons were made. Based on these results an adjustment unit was integrated in a miniaturized interferometer system: After a short self-adjusting procedure lateral to the setup by overlaying two targets of a highly sensitive optical system the correct measuring distance between the cornea and the vibrometer parallel to the optical axis is determined automatically by an astigmatic auto-focus system. With this handheld-vibrometer in vivo measurements with several test persons were made with very good results concerning the reliability and handling capability.

Glaucoma causes irreversible damage to nerves in the retinal nerve fiber layer. A technique that could measure both the condition and thickness of the retinal nerve fiber layer (RNFL) would be very useful for the early detection and treatment of glaucoma. Polarization Sensitive Optical Coherence Tomography (PS-OCT) is a modality that measures the depth resolved optical birefringence of biological tissue. Since damage to the nerve fiber layer could decrease its birefringence, PS-OCT has the potential to enhance specificity in determining RNFL thickness and integrity in OCT images. In order to measure the RNFL birefringence on humans in vivo, a fiber-based PS-OCT set-up was built with which quasi real time images of the human retina were made. Preliminary measurements on a healthy retina show that the birefringence of the RNFL around the optic nerve head was equal to 34+/- 3 degree(s)/100 micrometers . In conclusion, to our knowledge, we present the first depth resolved birefringence measurements of the human RNFL in vivo.

Imaging the optical phase retardation per unit depth (OPR/UD) in the retinal nerve fiber layer (RNFL) may aid in glaucoma diagnosis. Polarization Sensitive Optical Coherence Tomography (PSOCT) was used to record in vivo high-resolution images of the RNFL in two cynomologous monkeys. The depth variation in the Stokes vector of reflected light was used to calculate the OPR/UD as a function of RNFL position. OPR/UD decreased from 35 degree(s)/100 micrometers near the optic nerve to 5 degree(s)/100 micrometers at a location 600 micrometers superior to the optic nerve. Variation of OPR/UD in the RNFL with retinal position demonstrates a change in birefringence for different densities of ganglion cell axons. PSOCT may be useful for noninvasive determination of RNFL thickness and fiber density.

Glaucoma is a set of diseases that cause optic nerve damage and visual field loss. The most important risk factor for the development of glaucoma is elevated intraocular pressure. One approach used to alleviate the pressure increase is to surgically install glaucoma implants. Two standard Ahmed and ten experimental ePTFE implants were evaluated in this study in rabbit eyes. The implants were imaged with optical coherence tomography (OCT) at 0, 7, 15, 30, and 90 days after implantation. Histology was collected at days 7, 15, 30, and 90 and compared to the OCT images. Preliminary analysis of images indicates that OCT can visualize the development of fibrous encapsulation of the implant, tissue erosion, fibrin accumulation in the implant tube, and tube position in the anterior chamber. A new OCT handheld probe was developed to facilitate in vivo imaging in rabbit eye studies. The OCT probe consists of a mechanical scaffold designed to allow the imaging fiber to be held in a fixed position with respect to the rabbit eye, with minimal anesthesia. A piezo electric lateral scanning device allows the imaging fiber to be scanned across the tissue so that 2D images may be acquired.

Laser induced ultrasound provides a powerful tool for solving a major problem of laser cyclophotocoagulation, which is caused by difficulties in localization and determination of optical properties. Furthermore it adds the possibility of an online control mechanism for the process of coagulation of the ciliary body. We have developed a transducer system which is based on a fiber with 600 micrometers core diameter surrounded by a ring shaped piezoelectric PVDF detector. With this detector it is possible to localize the lateral position of the ciliary body on enucleated pigs and rabbit eyes as well as its depth. Our findings correspond well with histological sections of the measured area. Additionally, the changes in the tissue's optical properties induced by coagulation with a diode laser have been detected in real time.

We have presented experimental data on in vivo and in vitro study on the optical clearing of the scleral tissue controlled by administration of the osmotic liquids. For example, administration of glucose induces matter diffusion and as a result equalization of the refractive indices of scleral tissue scatterers and interstitial fluid. The significant increase of transmittance and decrease of reflectance of the sclera under glucose solution action have been demonstrated. The glucose diffusion coefficient has been estimated. The results of in vitro study of polarization features of scleral optical transmittance at tissue clearing are also presented.

Laser photocoagulation is a well-established treatment modality for a variety of retinal disorders, but is difficult to use near the fovea due to thermal retinal destruction. Certain diseases, such as drusen maculopathy, are thought to be caused by a dysfunction of the Retinal Pigment Epithelium. For those diseases selective targeting of the RPE, sparing the adjoining photoreceptors, might be the appropriate treatment to avoid laser scotoma, as it has been shown with application of a train of ms laser pulses by Birngruber and Roider. Our new approach is to use a conventional green cw laser and rapidly scan a small laser spot over the retina so as to produce microsecond(s) -illumination at each RPE cell. Two scanning devices were developed using acousto-optic deflectors. For the in vitro experiments the ED₅₀ value RPE cell damage was 170 mW with 100 exposures, scanning with a speed of 1 spot diameter/3 microsecond(s) . In vivo experiments demonstrated an angiographic ED₅₀ threshold of 66 mW for 100 exposures while scanning with an effective illumination time of 5 microsecond(s) . The ophthalmoscopic threshold was higher than a factor of 2 times the angiographic ED₅₀. Using separated scan lines we show selectivity in the form of surviving cells in between irradiated lines. Selective destruction of RPE cells is possible using laser-scanning devices.

Occlusions of the retinal veins and arteries are associated with common diseases such as hypertension and arteriosclerosis and usually cause severe and irreversible loss of vision. Treatments for these vascular diseases have been unsatisfactory to date in part because of the difficulty of delivering thrombolytic drugs locally within the eye. In this article we describe a pulsed liquid microjet for minimally invasive intra-vascular drug delivery. The microjet is driven by a vapor bubble following an explosive evaporation of saline, produced by a microsecond-long electric discharge in front of the 25 micrometers electrode inside the micronozzle. Expansion of the transient vapor bubble produces a water jet with a diameter equal to the diameter of the nozzle, and with a velocity and duration that are controlled by the pulse energy. We found that fluid could be injected through the wall of a 60-micrometers -diameter artery in choriallantoic membrane using a 15-micrometers diameter liquid jet traveling at more than 60 m/s. Histological analysis of these arteries showed that the width of the perforation is limited to the diameter of the micronozzle, and the penetration depth of the jet is controlled by the discharge energy. The pulsed liquid microjet offers a promising technique for precise and needle-free intravascular delivery of thrombolytic drugs for localized treatment of retinal vascular occlusions.

A simulator for phacoemulsification cataract extraction is developed. A three-dimensional visual interface and foot pedals for phacoemulsification power, x-y positioning, zoom and focus were established. An algorithm that allows real time visual feedback of the surgical field was developed. Cataract surgery is the most common surgical procedure. The operation requires input from both feet and both hands and provides visual feedback through the operation microscope essentially without tactile feedback. Experience demonstrates that the number of complications for an experienced surgeon learning phacoemulsification, decreases exponentially, reaching close to the asymptote after the first 500 procedures despite initial wet lab training on animal eyes. Simulator training is anticipated to decrease training time, decrease complication rate for the beginner and reduce expensive supervision by a high volume surgeon.

Our previous studies using rabbits and monkeys showed that the Amide II wavelength (6.45 micrometers ) produced by the FEL could efficiently produce an optic nerve sheath fenestration with minimal damage. In order to determine if the technology safely could be applied to human surgery, we used 2 blind human eyes during enucleation to compare the results of producing fenestrations with the FEL or a scissors. FDA and Vanderbilt IRB approvals, and individual patient consents were obtained. The FEL energy was transmitted to a human operating room. After disinsertion of the medial rectus muscle, an optic nerve sheath fenestration (2 mm diameter) was made with either the FEL (6.45 micrometers , 325 micrometers spot size, 30 Hz, 3 mJ) through a hollow waveguide surgical probe or with a scissors. The enucleation was then completed. The optic nerve was dissected from the globe and fixed. Specimens were examined histologically. Dural incisions were effective with both methods. FEL energy at 6.45 micrometers can be transmitted to an operating room and delivered to human ocular tissue through a hollow waveguide surgical probe. This FEL wavelength can produce an optic nerve sheath fenestration without acute direct damage to the nerve in this case report.

For the first time the effect of the UV laser radiation to human eye cornea with herpetic keratitis was experimentally investigated. In experiments the UV radiation of ArF (193 nm), KrCl (223 nm), KrF (248 nm) excimer lasers were used. Optimal laser radiation parameters for the treatment of the herpetic keratitis were determined. The immuno-biochemical investigations were carried out and the results of clinical trials are presented. The maximum ablation rate was obtained for the 248 nm radiation wavelength. The process of healing was successful but in some cases the haze on the surface of the cornea was observed. When used the 193 nm radiation wavelength the corneal surface was clear without any hazes but the epithelization process was slower than for 248 nm wavelength and in some cases the relapse was occurred. The best results for herpetic keratitis treatment have been achieved by utilizing the 223 nm radiation wavelength of the KrCl excimer laser. The use of the 223 nm radiation wavelength allows treating the herpetic keratitis with low traumatic process of ablation and provides high quality of corneal surface.

Purpose. The purpose of this study was to develop a model to predict the corneal temperature and shrinkage during laser thermokeratoplasty and other clinical procedures relying on laser-induced thermal shrinkage of collagenous tissue. Methods. The corneal temperature was calculated by solving the bio-heat equation during laser irradiation using a semi-analytical technique. To calculate shrinkage, we assumed that corneal thermal shrinkage is a thermal denaturation process that follows an Arrhenius equation, and that shrinkage resulting from denaturation is proportional to the amount of thermal damage. We calculated shrinkage for pulsed Ho:YAG laser thermokeratoplasty using the clinical treatment algorithm. Results. The thermal model predicts that the corneal temperature reaches values that may be high enough to induce surface vaporization of the epithelium and thermal damage of the endothelium. Shrinkage calculations show that significant shrinkage is produced only after the third laser pulse. Shrinkage is produced mainly during laser pulses and stops shortly after the start of the cooling phase between laser pulses. Conclusions. These calculations demonstrate that thermal shrinkage can be predicted by combining an optical-thermal model and a thermal denaturation model. Accurate quantitative prediction of the shrinkage effect requires a better knowledge of the dynamics of shrinkage and of the optical thermal response of the cornea.

Accurate prediction of LTK treatments requires refined thermal corneal models which necessitate precise input parameters. The overall objective of this study was to provide detailed information on the spatiotemporal temperature profile of the corneal surface, during in-vitro thermal keratoplasty. LTK was performed in-vitro on freshly harvested porcine eyes (N equals 16) with the Sunrise Technologies corneal shaping system (Model SUN 1000). Spatiotemporal thermal imaging of the irradiated corneas were obtained with a short wave Inframetrics thermal camera (Model PM290). Images were obtained at 8-bits resolution, with ~100 microns spatial and ~17 msec temporal resolution respectively. Treatment pattern consisted of eight spots at 6 mm zone, while lasing was conducted at settings of either 100 mJ and 15 pulses (N equals 8), or 260 mJ and 7 pulses (N equals 8). Temporal and spatial variation of the corneal surface temperatures were calculated at locations of importance to LTK. At the laser spot, temperature profiles consisted of transients coinciding approximately with the laser pulses. Maximum transient temperatures observed were 98.0+/- 4.6 degree(s)C for the high and 56.3+/- 2.6 degree(s)C for the low energy respectively. These temperature transients were superimposed on an envelope of lower-slowly varying temperatures. The maximum temperatures observed for this temperature envelope, were 51.8+/- 3.4 degree(s)C for the high and 35.4+/- 3.4 degree(s)C for the low energy respectively. The evolution of either the maximum temperature transients or the lower temperature envelope, followed exponential growth of the form: T equals A * exp(B*t). Maximum temperatures at locations 0.5 mm and 1 mm away from the laser spot, reached 25.7 degree(s)C and 23.3 degree(s)C for the low energy, and 34 degree(s)C and 25.6 degree(s)C for the high energy settings respectively. Temperature decay constants were approximately 2 to 3 sec, while the spatial temperature profile at the laser spot extended more than 2 mm at 2.5 sec post irradiation. The data obtained may help to refine corneal thermal modeling during LTK, and thus improve predictability of current or future-modified-treatments.

The purpose of this study was to design and calibrate a device to measure the dynamics of thermal shrinkage in corneal and scleral strips. The apparatus consists of a thermoelectric cell controlled by a temperature controller designed to generate temperatures up to 90 degree(s)C in rectangular corneal strips; a copper cuvette filled with Dextran solution that holds the corneal strip and a displacement sensor that measures the change in length of the tissue during heat-induced shrinkage. The device was tested on corneal tissue from Florida Eye-Bank eyes that were cut into 2x4mm rectangular strips. Preliminary results indicate that our system can reproducibly create and accurately measure thermally induced corneal shrinkage. Shrinkage experiments will be used to optimize laser parameters for corneal shrinkage during laser thermokeratoplasty and laser scleral buckling.

Purpose. Experimentally find a method to provide a safe surgical technique and an inexpensive and long lasting mesoplant for the restoration of vision in patients with bilateral corneal blindness due to ocular surface and stromal diseases. Methods. Identify the least invasive and the safest surgical technique for synthetic cornea implantation. Identify the most compatible biomaterials and the optimal shape a synthetic cornea must have to last a long time when implanted in vivo. Results. Penetrating procedures were deemed too invasive, time consuming, difficult and prone to long term complications. Therefore a non-penetrating delamination technique with central trephination was developed to preserve the integrity of Descemet's membrane and the anterior segment. Even though this approach limits the number of indications, it is acceptable since the majority of patients only have opacities in the stroma. The prosthesis was designed to fit in the removed tissue plane with its skirt fitted under the delaminated stroma. To improve retention, the trephination wall was made conical with the smallest opening on the anterior surface and a hat-shaped mesoplant was made to fit. The skirt was perforated in its perimeter to allow passage of nutrients and tissues ingrowths. To simplify the fabrication procedure, the haptic and optic were made of the same polymer. The intrastromal biocompatibility of several hydrogels was found superior to current clinically used PMMA and PTFE materials. Monobloc mesoplants made of 4 different materials were implanted in rabbits and followed weekly until extrusion occurred. Some remained optically clear allowing for fundus photography. Conclusions. Hydrogel synthetic corneas can be made to survive for periods longer than 1 year. ArF excimer laser photoablation studies are needed to determine the refractive correction potential of these mesoplants. A pilot FDA clinical trial is needed to assess the mesoplant efficacy and very long-term stability.

Spectacle mounted telescopic systems have been prescribed for visual impairment, providing magnified images of objects at farther distances. Typically, bioptic telescopes are mounted toward the top of spectacle lenses or above the frame with the telescope eyepiece positioned above the eye's pupil. This allows the wearer to alternate between the magnified narrow field of view available through the eyepiece and the unmagnified wide view through the carrier lens using head motion. The main obstacles to acceptance are the obvious appearance, limited field of the smaller Galilean telescopes, and weight of the larger Keplerian telescopes. We designed a spectacle-mounted wide-field Keplerian telescope built completely inside the spectacle lens. The design uses embedded mirrors inside the carrier lens for optical pathway folding and conventional lenses or curved mirrors. The small size of the ocular and its position with additional mirror tilt enable the user to view the magnified field simultaneously and above the unmagnified view of the uninterrupted horizontal field that is important for user's safety. This design enables the construction of cosmetic telescopes that can be produced as a commodity lens blank and surfaced to include the patient prescription. These devices may be also of utility in military and civilian use.

In order to perform refractive surgery, fs-laser pulses of 130-fs pulse duration were focused into animal cornea. By focusing the radiation down to spot-sizes of 5 micrometers , very precise cuts could be achieved inside the treated eyes, accompanied with minimum collateral damage to the tissue by thermal or mechanical effects. Due to these low side effects, micrometers -cutting precisions at preparing of corneal flaps and lenticules can be achieved. Thus, animal studies with 8 living rabbits were performed, in which intrastromal lenticules and flaps were created and extracted. Wound healing reactions were studied by histo- pathological analysis of the treated eyes in intervals at one, 7, 14 and 28 days after surgery. The treated eyes showed mild wound healing reactions with comparable results to what is known from Excimer-LASIK. Moreover the use of the fs-laser offered new possibilities in preparation of corneal flaps, providing advantages to the use of the mechanical keratome.

A study was undertaken to assess whether results of laser vision correction with the LADARVISION 193-nm excimer laser (Alcon-Autonomous technologies) can be improved with the use of wavefront analysis generated by a proprietary system including a Hartman-Schack sensor and expressed using Zernicke polynomials. A total of 82 eyes underwent LASIK in several centers with an improved algorithm, using the CustomCornea system. A subgroup of 48 eyes of 24 patients was randomized so that one eye undergoes conventional treatment and one eye undergoes treatment based on wavefront analysis. Treatment parameters were equal for each type of refractive error. 83% of all eyes had uncorrected vision of 20/20 or better and 95% were 20/25 or better. In all groups, uncorrected visual acuities did not improve significantly in eyes treated with wavefront analysis compared to conventional treatments. Higher order aberrations were consistently better corrected in eyes undergoing treatment based on wavefront analysis for LASIK at 6 months postop. In addition, the number of eyes with reduced RMS was significantly higher in the subset of eyes treated with a wavefront algorithm (38% vs. 5%). Wavefront technology may improve the outcomes of laser vision correction with the LADARVISION excimer laser. Further refinements of the technology and clinical trials will contribute to this goal.

Most corneal topographers are slope-based instruments, measuring corneal slope based on light reflected by the cornea acting as a mirror. This mirror method limits corneal coverage to about 9 mm diameter. Both refractive surgery and contact lens fitting actually require a larger coverage than is obtainable using slope-based instruments. Height-based instruments should be able to measure a cornea/sclera area that is twice the size (four times the area) of slope-based topographers with an accuracy of a few microns. We have been testing a prototype of a new model height-based topographer manufactured by Euclid Systems. We find that single shots can produce a corneal coverage of up to 16 mm vertical and 20 mm horizontal. The heights and slopes in the corneal region have good replicability. Although the scleral region is noisier, it is the only topographer available able to measure scleral topography that is critically important to contact lens fitting. There are a number of improvements to the Euclid software and hardware that would enable it to fill an important niche in eye care and eye research.

Purpose: Local variations in refractive index are an important physical cause of light scattering in the lens. The goal of this study was to further add to the understanding of the process of light propagation in the lens by directly measuring local variations in refractive index by phase contrast microscopy. Methods: Refractive index was estimated by immersion refractometry. Cryo-sections of quick frozen human donor lenses were embedded in a graded series of bovine serum albumin solutions, and in immersion oil. Results: Superficial cortical fiber membranes proved to have a refractive index considerably above values given for cytoplasm at the same location. Nuclear fiber membranes have a refractive index of the same order as given in the literature for nuclear fiber cytoplasm. Conclusion: The large difference in refractive index between fiber membranes and cytoplasm in the lens cortex may be important for optical function and transparency of the lens. Support: Marie Curie Fellowship of the European Community program Quality of Life (QLK6-CT-1999-51159).

The subject of this paper relates to the ocular optical design and vision analysis of refractive correction of the eye. After the purpose statement and the assumption list, the concept of the schematic eye matching a particular (measured) wavefront is introduced. This concept is based on the fact that the ocular wavefront, together with the corneal topography, can be seen as the mathematical global representation of the eye working in monochromatic light and having a foveal vision. The discussed design technique, including an iterative optimization method, could be applied in any ocular correction that utilizes cornea topography and/or ocular wavefront, e.g. contact lens or intra-corneal implant. However, the application this paper refers to is the ocular refractive correction by a procedure using the LADARVISION. It consists of surgical removal and subsequent replacement of a corneal flap on a stromal surface whose shape has been changed by laser ablation of the tissue. Subsequent sections of this paper are dedicated to establishing the limits of possible refractive correction, the influences of the flap and corneal topography into the refractive correction calculation. Finally a realistic evaluation of the results and a list of possible developments of this new optical design method are discussed.

Purpose: Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality at the retina depends on all optical elements of the eye such as the human lens. Thus, the aim of this study was to investigate the correlations between the corneal and total wavefront aberrations and to discuss the importance of corneal aberrations for representing corneal laser surgery results. Methods: Thirty three eyes of 22 myopic subjects were measured with a corneal topography system and a Tschernig-type wavefront analyzer after the pupils were dilated to at least 6 mm in diameter. All measurements were centered with respect to the line of sight. Corneal and total wavefront aberrations were calculated up to the 6th Zernike order in the same reference plane. Results: Statistically significant correlations (p < 0.05) between the corneal and total wavefront aberrations were found for the astigmatism (C3,C5) and all 3rd Zernike order coefficients such as coma (C7,C8). No statistically significant correlations were found for all 4th to 6th order Zernike coefficients except for the 5th order horizontal coma C18 (p equals 0.003). On average, all Zernike coefficients for the corneal aberrations were found to be larger compared to Zernike coefficients for the total wavefront aberrations. Conclusions: Corneal aberrations are only of limited use for representing the optical quality of the human eye after corneal laser surgery. This is due to the lack of correlation between corneal and total wavefront aberrations in most of the higher order aberrations. Besides this, the data present in this study yield towards an aberration balancing between corneal aberrations and the optical elements within the eye that reduces the aberration from the cornea by a certain degree. Consequently, ideal customized ablations have to take both, corneal and total wavefront aberrations, into consideration.

The effect of lateral and torsional misalignments of the ablation on the postoperative optical outcome was theoretically investigated based on measured wavefront aberration data from 130 normal eyes. Simulations included lateral decentrations and rotations around the longitudinal axis of the eye (torsion). The optical quality of the simulated refractive correction was rated by means of the root-mean-squared residual wavefront error. The accuracy for lateral centration in order to achieve the diffraction limit at a pupil size of 8 mm in 95% of the investigated eyes should be 50 microns or better. However, an accuracy of 450 microns was found to be enough to guarantee that none of the investigated eyes would suffer from a decreased optical performance after surgery. Alignment would have to be performed with a torsional precision of approximately 1 deg or better in order to achieve the diffraction limit in 95% of the measured normal eyes for an 8-mm pupil, whereas an accuracy of 15 deg is required to obtain at least some improvement of the optical quality in all the examined eyes. The accuracy needed for torsional alignment increases compared to pure sphero-cylindrical treatments when additional correction of the higher-order aberrations is aspired.

We have generated high spatial resolution images showing the distribution of carotenoid macular pigments in the human retina using Raman spectroscopy. A low level of macular pigments is associated with an increased risk of developing age-related macular degeneration, a leading cause of irreversible blindness. Using excised human eyecups and resonant excitation of the pigment molecules with narrow bandwidth blue light from a mercury arc lamp, we record Raman images originating from the carbon-carbon double bond stretch vibrations of lutein and zeaxanthin, the carotenoids comprising human macular pigments. Our Raman images reveal significant differences among subjects, both in regard to absolute levels as well as spatial distribution within the macula. Since the light levels used to obtain these images are well below established safety limits, this technique holds promise for developing a rapid screening diagnostic in large populations at risk for vision loss from age-related macular degeneration.

A digital control unit for use with a new integrated instrument for dynamic light scattering and natural fluorescence measurements is presented. This unit, based on a microcontroller (Microchip PIC16F877), process signals from an optical head and controls instrument functions. The microcontroller internal counters are used to perform real- time photon counting measurement by processing the TTL signals obtained from the photodetectors. The new system provides reliable and simultaneous DLS and AF measurements from the same ocular volume located from the cornea to the retina.

Dynamic light scattering (DLS) and autofluoresence (AF) are two promising optical diagnostic techniques for use in ophthalmology. In this paper the DLS and AF are integrated in one instrument and applied to study healthy and pathological ocular tissues to detect changes at the molecular level. Measurements performed on 17 patients (age range 20-80 years) are presented. Out of these, 7 patients were healthy normals, 10 had glaucoma and the two oldest patients had both glaucoma and cataracts.

A preliminary study of corneal abnormalities in intact bovine eyes is presented. Twenty-one eyes were treated with chemicals, cotton swabs, and radial and photo-refractive surgeries. Dynamic and static light scattering was performed as a function of the penetration depth into the corneal tissue. Topographical maps of corneal refractive power from untreated and treated corneas were also obtained using videokeratoscopy and results compared. The ultimate aim is to develop the technique of dynamic light scattering (DLS) for clinical applications in early evaluation of corneal complications after laser-assisted in situ keratomileusis (LASIK) surgeries and other corneal abnormalities.

An optical imaging device of retina function (OID-RF) has been constructed to record changes in reflected 700-nm light from the fundus caused by retinal activation in response to a visual 535-nm stimulus. The resulting images reveal areas of the retina activated by visual stimulation. This device is a modified fundus camera designed to provide a patterned, moving visual stimulus over a 45-degree field of view to the subject in the green wavelength portion of the visual spectrum while simultaneously imaging the fundus in another, longer wavelength range. Data was collected from 3 normal subjects and recorded for 13 seconds at 4 Hz; 3 seconds were recorded during pre-stimulus baseline, 5 seconds during the stimulus, and 5 seconds post-stimulus. This procedure was repeated several times and, after image registration, the images were averaged to improve signal to noise. The change in reflected intensity from the retina due to the stimulus was then calculated by comparison to the pre-stimulus state. Reflected intensity from areas of stimulated retina began to increase steadily within 1 second after stimulus onset and decayed after stimulus offset. These results indicated that a functional optical signal can be recorded from the human eye.

In all laser treatments at the fundus of the eye the temperature increase is unknown. In order to optimize the treatment modalities, a noninvasive online temperature determination is preferable. Applying laser pulses to the fundus, thermoelastic stress waves are emitted based on the thermal expansion of the heated tissue, mainly the retinal pigment epithelium (RPE). The amplitude of the thermoelastic wave is proportional to the thermal expansion coefficient, which linearly depends on temperature between 30-80 degree(s)C for water. The method was evaluated for selective RPE- treatment in vitro and clinically using the microsecond(s) -laser pulses for treatment and temperature determination simultaneously. Conventional laser photocoagulation was investigated in vitro using an Ar Ion laser for coagulation and low-energy N₂-pumped dye laser pulses to probe the temperature. In all cases, sufficient pressure amplitudes were detected either by a needle hydrophon in vitro or by a contact lens with embedded transducer during treatment. Depending on the treatment parameter, temperature increase of 60 degree(s)C were evaluated from the pressure transients. All temperatures detected are in close agreement to heat diffusion calculations. We demonstrated a noninvasive online method to detect retinal temperatures during laser treatments. This technique can be adapted to photocoagulation, PDT and TTT.

We have initiated experiments designed to test the hypothesis that 670-nm Light-Emitting Diode (LED) exposure will attenuate formate-induced retinal dysfunction in a rodent model of methanol toxicity. Methanol intoxication produces toxic injury to the retina. The toxic metabolite formed in methanol intoxication is formic acid, a mitochondrial toxin known to inhibit cytochrome oxidase activity. 670-nm LED light has been hypothesized to act by stimulating cytochrome oxidase activity. To test this hypothesis, one group of animals was intoxicated with methanol, a second group was intoxicated with methanol and LED-treated and a third group was untreated. LED treatment (670 nm for 1 min 45 seconds equals 50 mW/cm², 4 joules/cm²) was administered at 5, 25, and 50 hours after the initial dose of methanol. At 72 hours of methanol intoxication, retinal function was assessed by measurement of ERG responses and retinas were prepared for histologic analysis. ERG responses recorded in methanol-intoxicated animals revealed profound attenuation of both rod-dominated and UV-cone mediated responses. In contrast, methanol- intoxicated animals exposed to LED treatment exhibited a nearly complete recovery of rod-dominated ERG responses and a slight improvement of UV-cone mediated ERG responses. LED treatment also protected the retina against the histopathologic changes produced by formate in methanol intoxication. These data provide evidence that LED phototherapy protects the retina against the cytotoxic actions of formate and are consistent with the hypothesis that LED photostimulation improves mitochondrial respiratory chain function.

To (1) quantify changes in corneal topography induced by radial anterior sclerostomy for restoring accommodation and, (2) assess safety and ant fibrosis activity of cross-linked sodium hyaluronic acid (cSHA) based gels in ACS procedures. Methods (ex-vivo study): 6 fresh human Eye-Bank eyes were used. A 15% Dextran solution was injected in the anterior chamber and the vitreous cavity, the corneal epithelium was removed by scraping, and the whole eye was immersed in 15% Dextran solution until corneal thickness reached a physiological value. The conjunctiva and tenon capsule were removed and the eye was mounted on a custom-made holder. Preoperative corneal topography was measured with a PAR corneal topography system. Five to eight 3mm-long linear equidistant anterior radial incisions starting from the limbus were performed in the sclera at 90% depth with a diamond blade. Postoperative corneal topography was measured. The files providing the pre and postoperative tangential curvature along meridians separated by 5 degrees were exported. The axial curvature along the 0 and 90-degree meridians before and after surgery were compared. Methods (in-vivo study): Of 24 rabbits, 4 were operated following Thornton's (90% depth incision) and 20 following Fukasaku's (100% depth) techniques (total peritomy, four 4mm long radial scleral incisions starting 0.5 mm from the limbus).