Optical polarization study is performed on the healthy and neovascularized human retinal and retinal pigment epithelium (RPE)/choroidal tissues. Linear polarizer and polarizing analyzer have been employed to determine the intensity changes as well as polarization shifts of the polarized laser light scattered off these tissues from both the left and right eyes. Our studies show that both retinal and choroidal tissues possess strong polarization properties. The polarization shift is found to be higher in the neovascularized tissues than in the healthy tissues. It is also observed that the greater the polarization shift, the lower the intensity of the scattered light.

We have developed a specialized form of retinal birefringence scanning (RBS), in which a small spot of polarized light is scanned in a circle on the retina, and the returning light is measured for the changes in polarization cuased by the pattern of birefringent fibers that radiate from the fovea. Binocular RBS (BRBS) detects fixation of both eyes simultaneously and thus screens for strabismus, one of the risk factors of amblyopia. We have also developed a technique to automatically detect when the eye is in focus without measuring refractive error. This focus detector utilizes a bull's eye photodetector optically conjugate to a point fixation source. Reflected light is focused back to the point source by the optical system of the eye and if the subject focuses on the fixation source, the returning light will be focused on the detector. We have constructed a hand-held prototype combining BRBS and focus detection measurements in one quick (<0.5 second) and accurate (theoretically detecting ±1° of misalignment) measurement. Here we present our data of BRBS and focus detection signals in a number of normal and amblyopic subjects, demonstrating that this approach can reliably and effectively identify children at risk for amblyopia.

Polarization sensitive optical coherence tomography (PS-OCT) was used to measure and image retardation and birefringent axis orientation of in vitro human cornea. We used a two-channel PS-OCT system employing a phse sensitive recording of the interferometric signals in two orthogonal polarization channels. Using an algorithm based on a Hilbert transform, it is possible to calculate the retardation and the slow axis orientation of the sample with only one A-scan per transversal measurement location. While the retardation information is encoded in the amplitude ratio of the two interferometric signals, the axis orientation is encoded entirely in their phase difference. We present maps of retardation and slow axis distribution of normal and pathologic human cornea in longitudinal cross sections and en face images, obtained at the back sruface of the cornea. The results can be explained by a birefringence model based on stacked collagen fibril lamellae of different orientations.

We present in vivo depth-resolved birefringence measurements of the human retinal nerve fiber layer (RNFL) by use of polarization-sensitive optical coherence tomography (PS-OCT). Because glaucoma causes nerve fiber layer damage, which may cause loss of retinal birefringence, PS-OCT is a potentially useful technique for the early detection of glaucoma. We built a fiber-based PS-OCT setup that produces real-time images of the human retina in vivo, co-registered with video images of the location of PS-OCT scans on the retina. Preliminary measurements of a healthy volunteer showed that the double-pass phase retardation per unit depth of the RNFL varies with location with values in between 0.18 and 0.37°/μm. A trend in the preliminary measurements shows that thicker nerve fiber layer tissue is more birefringent than thin nerve fiber layer tissue.

One of the earliest signs of glaucoma presence is defects in the retinal nerve fiber layer (RNFL). Scanning laser polarimetry (SLP) provides objective assessment of RNFL, a birefringent tissue, by measuring the total retardation in the reflected light. SLP provides a potential tool for early detection of glaucoma and its progression. The birefringence of the anterior segment of the eye, mainly the cornea, is a confounding variable to SLP's clinical application, if compensation cannot be achieved properly. This paper presents a new SLP system, GDx VCC (Laser Diagnostic Technologies, Inc., San Diego, CA), with a variable corneal compensator (VCC) to achieve individualized corneal compensation. Clinical application of this device in glaucoma detection is also demonstrated.

Purpose: To develop a technique to assess isotonic solutions for crystalline lens preservation. Methods: BSS, Ringer’s, Dulbecco’s Modified Eagle Medium (DMEM), and TC 199 have been selected for experimentation. Donor human cadaver lenses are extracted by cutting the zonules and vitreous adherences. A custom-made testing cell and modified optical comparator are used for imaging, and the lens diameter and thickness profiles are measured using digital photography and a graphics program. Measurements are taken every 5 minutes for the 1st hour and then every 15 minutes for 4 hrs. The volume of the lens at each interval is approximated, assuming rotational symmetry, by using the equation for the volume of an ellipsoid. The changes in diameter, thickness, and volume versus time are analyzed to compare the effect of each solution. Results: The measurement resolution for the digital technique is 13μm. Lens thickness changed more significantly than diameter and volume. All four solutions produced similar preliminary results with maximum diameter, thickness, and volume changes of approximately -2%, +6%, and +3%, respectively. Conclusion: Shadowphotogrammetry can measure the lens physical dimensions to +/-13um and can be used to determine the effect of preservation media. This technique may be useful for assessing the physical effects of chemical and biological substances on the lens osmotic transport system.

Selective targeting of the Retinal Pigment Epithelium (RPE), by either applying trains of microsecond laser pulses or, in our approach, by repetitively scanning a tightly focused spot across the retina, achieves destruction of RPE cells while avoiding damage to the overlying photoreceptors. Both techniques have been demonstrated as attractive methods for the treatment of retinal diseases that are caused by a dysfunction of the RPE. Because the lesions are ophthalmoscopically invisible, an online control system that monitors cell death during irradiation is essential to ensure efficient and selective treatment in a clinical application. Bubble formation inside the RPE cells has been shown to be the cell damage mechanism for nano- and picosecond pulses. We built an optical system to investigate whether the same mechanism extends into the microsecond regime. The system detects changes in backscattered light of the irradiating beam during exposure. Samples of young bovine eyes were exposed in vitro using single pulses ranging from 3 μs to 50 μs. Using the viability assay calcein-AM the ED50 threshold for cell death was determined and compared to the threshold for bubble formation. We also set up a detection system on our slit lamp adapted scanning system in order to determine the feasibility of monitoring threshold RPE damage during selective laser treatment in vivo. Intracellular cavitation was detected as a transient increase in backscattering signal, either of an external probe beam or of the irradiation beam itself. Monitoring with the irradiation beam is both simpler and more sensitive. We found the threshold for bubble formation to coincide with the threshold for cell damage for pulse durations up to 20 μs, suggesting that cavitation is the main mechanism of cell damage. For pulse widths longer than 20 μs, the cell damage mechanism appears to be increasingly thermal as the two thresholds diverge. We conclude that bubble detection can be used to monitor therapeutic endpoint for pulse durations up to 20 μs (or equivalent dwell time in a scanning approach). We have integrated a detection module into our slit lamp adapted laser scanner in order to determine threshold RPE damage during selective laser treatment in vivo.

Precise and tractionless tools are needed for cutting and ablation of ocular tissue in such operations as vitreoretinal surgery, capsulotomy, non-penetrating trabeculectomy and many others. Previously we reported about the Pulsed Electron Avalanche Knife capable of tractionless dissection of soft tissue in liquid media using the 100 ns-long plasma-mediated electric discharges applied via a 25 um inlaid disk electrode. In this work we present a next step in the development of this technique, which dramatically improves its precision, the cutting rate and the scope of applicability. (1) Due to spherical geometry of the discharge with the disk-like microelectrode the width of the cut was equal to its depth. To overcome this limitation we apply now a thin cylindrical electrode where the width and the depth of the cut are controlled independently. (2) Cavitation accompanying the sub-microsecond explosive evaporation was a major limiting factor in precision of this technique. In a new modality we apply bursts of pulses, which allow for much higher energy deposition without increase in the size of the transient vapor cavity. (3) Coagulation regime for blood vessels larger than 25 microns in diameter was not possible in the initial approach. It is now available due to extension of the electrode in one dimension. (4) Increase in pulse duration up to several tens of microseconds allows for reduction in voltage and, consequently, in width of the insulator. This, in turn, enables development of the ultra-thin electrodes that can be applied via an intraocular endoscope or 25 G needles. The new device was found capable of rapidly and precisely dissecting virtually all types of ocular tissue: from soft membranes to cornea and sclera. In addition to vitreoretinal surgery it applications can now expand into anterior chamber surgery including capsulotomy and trabeculectomy.

We have developed a simulator for phacoemulsification cataract extraction. In the current project, modules for clinical evaluation were developed. The system was structured into a processing computer and an administrator interface and a trainee interface. The simulation is defined by administrator adjustable parameters and trainee adjustable parameters. The parameters may be categorized as session characteristic parameters, patient characteristic parameters and trainee characteristic parameters. The simulation is measured in variables. Further an air bubble generator was created. We believe that simulator training in future will be required for becoming cataract surgeons.

Purpose: To assess the effects of immersion solutions with different Dextran concentrations on the hydration of cornea tissue strips at normal body temperature. Methods: A 20% Dextran-BSS solution was injected via a self sealing limbal-transcorneal tunnel incision using a 30ga needle into the anterior chamber of human donor eyes until the globe was hard. The eyes were then immersed cornea down overnight in the same solution. Corneal thickness was measured by ultrasound pachymetry after the eyes were re-inflated and at regular intervals to assess dehydration. When the central cornea thickness reached 400-500μm corneal buttons were removed using a 10mm trephine. The buttons were then cut into 6×6mm strips using a custom-made jig and immediately immersed in solutions of Dextran (15 to 20% in increments of 2.5%) at 35°C. The edge thickness of the immersed strip was measured every 5 min for one hour using an optical comparator (Topcon, Japan) modified for tissue shadowphotogrammetry. Results: For five Florida Lions Eye Bank donated eyes after one hour in the Dextran solution the mean final measured thickness of corneas in 20%, 17.5% and 15% Dextran-BSS solutions were 570 (±75) μm, 680 (±70) μm, and 1080 (±95) μm respectively. These measured thicknesses changes correspond to an average swelling of 1.2, 1.4 and 2.2 times the initial thickness of each cornea strip in the 20%, 17.5% and 15% Dextran-BSS solutions respectively. Conclusion: This study demonstrates hydration has a significant effect on the thermal stability and shrinkage dynamics of the cornea. A 25% Dextran solution was found to keep corneal tissue strip thickness at normal values.

Purpose: The purpose of this work was to develop a model to predict and compare laser-trabecular meshwork interactions during laser trabeculoplasty with three different lasers. Methods: A qualitative multilayer optical-thermal model of the trabecular meshwork was developed. The model was used to estimate the penetration depth and heat diffusion volume during laser trabeculoplasty with a continuous wave argon laser (ALT), a Q-switched frequency-doubled Nd:YAG laser (SLT), and a flashlamp-pumped near-infrared alexandrite or titanium sapphire laser emitting microsecond pulses (μs-IRLT). Results: The model predicts that both SLT and μs-IRLT produce selective heating of pigmented trabecular meshwork cells with negligible heat diffusion to surrounding structures and with a deeper penetration at the IR wavelength. A preliminary quantitative analysis indicates that selective targeting of spherical pigments is achieved as long as the pulse duration remains less than approximately 1μs. Conclusion: The qualitative model indicates that infrared laser trabeculoplasty with microsecond pulses can produce selective targeting of pigemented trabecular meshwork cells with a deeper penetration than SLT.

The potential of ns pulses of 266 nm from a frequency shifted Nd:YAG laser for corneal ablation was tested on human eye bank eyes. Scanning electron microscopy demonstrated that consecutive pulses in the same spot induced thermal damage that was related to the pulse energy. The ablation threshold was estiamted to 4.5 J/cm². The ablation per pulse slightly above threshold was 0.2-0.6 μm. It is concluded that the precision of the ablation is relevant for refractive ablations of the cornea. The higher radiation exposure required for corneal ablation at 266 nm compared to that for shorter wavelengths induces higher energy load on the cornea. To avoid heat build-up, a random flying spot is probably needed.

The Er:YAG laser (λ=2.94μm) is an effective tool in vitreo-retinal surgery. Pulsed mid-infrared (λ=6.45μm) radiation from the Free Electron Laser has been touted as a potentially superior cutting tool. To date, use of this laser has been limited to applications in an air environment. The goal of this study was: 1) determine feasibility of fiberoptic delivery of λ= 6.45μm using silverhalide fibers (d=700μm); 2) use infrared transparent vitreous substitute (perfluorodecalin) to allow non-contact ablation of the retina at λ= 6.45μm. Fiber damage threshold=7.8J/cm² (0.54GW/cm²) while transmission loss=0.54dB/m, allowing supra-ablative radiant exposures to the target. FTIR measurements of perfluorodecalin at λ=6.45μm yielded μ_a=3 mm^-1. Pump-probe imaging of ablation of a tissue-phantom through perfluorodecalin showed feasibility of non-contact ablation at λ=6.45μm. Ablation of the retinal membranes of enucleated pig eyes was carried out under perfluorodecalin (2 Hz, 1.3 J/cm²). Each eye was cut along its equator to expose the retina. Vitreous was replaced by perfluorodecalin and laser radiation was delivered to the retina via the silverhalide fiber. The eye was rotated (at 2 rpm) to create an ablation circle around the central axis of the retina. Histological analysis of the retina in a limited number of eyes shows that retina ablation using this method is feasible and can be accomplished with minimal collateral damage. Remote structures are shielded, as the radiation exposure falls below the ablation threshold owing non-negible absorption of perfluorodecalin at λ=6.45μm. This may optimize efficacy and safetly of laser-based vitreoretinal surgery.

The central part of a PMMA or acrylic resin lens was modified into hydrophobic and the peripheral part to be phydrophilic using teh ArF laser and excimer lamp. PMMA or acrylic resin lens have been used as an intraocular lens for 50 years and is the golden standard in ophthalmology. However, protein and fat are stuck onto the IOL surface after long-term implantation and opacify the surface )after-cataract). Therefore, the central part of the IOL was modified to be hydrophobic to prevent fat and protein deposition; the periphery was made hydrophilic to develop affinity for tissue.

Many different types of intraocular lenses (IOL) are currently available for implantation, both as crystalline lens replacements and as phakic refractive elements. Their optical design is increasingly sophisticated, including aspherical surface profiles and multi-zone multifocal structures, however a quantitative and comparative characterization of their imaging properties is lacking. Also a qualitative visualization of their properties would be very useful for patients in the lens choice process. To this end an experimental eye model has been developed to allow for simulated in-vivo testing of IOLs. The model cornea is made of PMMA with a dioptric power of 43 D, and it has an aspherical profile designed to minimize spherical aberration across the visible spectrum. The eye model has a variable iris and a mechanical support to accomodate IOLs, immersed in physiological solution. The eye length is variable and the retina is replaced by a glass plate. The image formed on this "retina" is optically conjugated to a CCD camera, with a suitable magnification in order to mimic the human fovea resolution, and displayed onto a monitor. With such an opto-mechanical eye model, two types of images have been used to characterize IOLs: letter charts and variable contrast gratings, in order to directly simulate human visual acuity and contrast sensitivity.

We developed a new point spread function (PSF) analysis system (PSFAS) to study the optical system of the human eye. An infrared point light source is projected on the retina, then the single-pass modulation transfer function (MTF) is derived from teh iamge of incoherent polarized reflection double-pass PSF measured by PSFAS. The retinal images and the contrast characteristics of various sized Landolt's rings then are simulated with the single-pass PSF calculated by the single-pass MTF. The visual acuity (VA) is predicted from the retinal images. The single-pass MTF and the contrast characteristics of aged subjects were clearly lower than those of a young subject in mid-frequency, though the cut-off frequency was similar in the two subjects. The predicted VA from the simulated retinal images agreed with the actual VA in normal subjects and in those with myopic astigmatism. This becomes a useful system for elucidating the optical characteristics of the human eye. In addition, the visual simulation obtained using this system is clinically useful for objectively evaluating visual function.

We show first deep UV ablation results achieved with our new all solid state laser system. The system parameters allow high repetition rate ablation with a small spot diameter of about 0.250mm and a fluence of 350 mJ/cm² at a wavelength of 210 nm using sequential frequency conversion of a diode pumped laser source. The single shot and multishot ablation rates as well as the ablation profiles have been defined using MicroProf (Fries Research and Technology GmbH, Germany). By means of computer controlled scanning we produce smooth ablation profiles corresponding to a correction of myopia, hyperopia or astigmatism. Due to the small spot size and high repetition rate of the laser we are able to generate in short time intervals complicated ablation profiles described by higher order polynomial functions which are required for the needs of customized corneal ablation.

Because of concerns about potential hazards to surgical personnel of the plume associated with laser refractive surgery, this study was performed to characterize the composition of such plumes. Filter elements were removed from the smoke evacuator of a VISX S3 excimer laser (filter pore size ~0.3 microns) and from a Mastel Clean Room ( filter pore size ~0.2 microns) used with a LADARVISION excimer laser. The filters from both laser systems captured the laser-induced plumes from multiple, routine, LASIK patient procedures. Some filters were processed for scanning electron microscopy, while others were extracted with methanol and chloroform for biochemical analysis. Both the VISX "Final Air" filter and the Mastel "Clean Room" filter captured material that was not observed in filters that had clean operating room air only passed through them. In the VISX system, air flows through the filter unit parallel to the filter matrix. SEM analysis showed these filters captured discrete particles of 0.3 to 3.0 microns in size. In the Mastel Clean Room unit, air flows orthogonally through the filter, and the filter matrix was heavily layered with captured debris so that individual particles were not readily distinguished. Amino acid analysis and gel electrophoresis of extracted material revealed proteinaceous molecules as large as 5000 molecular weight. Such large molecules in the laser plume are not predicted by the existing theory of photochemical ablation. The presence of relatively large biomolecules may constitute a risk of allergenic reactions in personnel exposed to the plume, and also calls into question the precise mechanism of excimer laser photochemical ablation.

Soft contact lenses (SCL) incorporating aberration-correction have the potential of providing acuity improvements beyond those offered by traditional spherical surface SCL. With the availability of such SCL offered by manufacturers, it is worthwhile to consider the extent of benefits such designs offer. One factor that can potentially influence the performance of aberration-corrected SCL is the optical effect introduced by the post-lens tear film (PoTLF). We modelled the optical impact of the PoTLF assuming three models: (1) worst case (2) representative Zernike surfaces, and (3) most-probable case. PoTLF parameters were based on measured or modelled values from previous studies. The optical contributions of the PoLTF was modelled as a pair of standard aspheric surfaces representing the posterior SCL surface and the anterior corneal/epithelial surface with r_o=7.80, k=-0.26. For each model, we analysed the MTF and calculated the Strehl ratio as a result of the optical aberrations introduced by PoTLF. Our results suggest that the PoTLF introduces a detectable amount of degradation in images and may slightly limit the visual benefits from aberration-corrected SCL. However, compared to the performance of traditional spherical surface SCL, we predict that worthwhile visual improvements should still be afforded by aberration-corrected SCL.

Purpose: To measure ocular aberrations before and at several time periods after LASIK surgery to determine the change to the aberration structure of the eye. Methods: A Shack-Hartmann wavefront sensor was used to measure 88 LASIK patients pre-operatively and at 1 week and 12 months following surgery. Reconstructed wavefront errors are compared to look at induced differences. Manifest refraction was measured at 1 week, 1 month, 3 months, 6 months and 12 months following surgery. Sphere, cylinder, spherical aberration, and pupil diameter are analyzed. Results: A dramatic elevation in spherical aberration is seen following surgery. This elevation appears almost immediately and remains for the duration of the study. A temporary increase in pupil size is seen following surgery. Conclusions: LASIK surgery dramatically reduces defocus and astigmatism in the eye, but simultaneously increases spherical aberration levels. This increase occurs at the time of surgery and is not an effect of the healing response.

Pigment dispersion syndrome and pigmentary glaucoma are investigated by a scanning instrument based on dynamic light scattering technique. The measurements are oriented to evaluate the various conjectures about the pathogenesis of pigmentary glaucoma and to establish a diagnostic tool that may be used for an early detection of this type of glaucoma.

We present static and dynamic light scattering measurements of early onset cataract before opacity is observed and an evaluation of the effectiveness of pantethine on protein aggregation and light scattering.

In this paper we present preliminary measurements on the effects of zero gravity environment on the choroidal blood flow on human volunteer subjects. These experiments were conducted, for the first time, on-board a wide body aircraft (KC-135) during parabolic flight trajectories (0g to 2g environment) using a head-mounted miniature laser Doppler flowmeter.

Clinical studies of carotenoid macular pigments (MP) and chronic retina disease have been limited by the lack of non-invasive, objective techniques. In this paper we describe anovel, noninvasive optical techniques based on the resonant Raman spectroscopy for the assessment of the carotenoid status of human retina in vivo. Using resonant excitation in the visible, we measure the Raman signals that originate from the single- and double-bond stretch vibrations of the π-conjugated carotenoid molecule's carbon backbone. MP Raman detector, robust device useful for routine measurements of MP concentration in a clinical setting, has been developed and tested in clinical studies in humans to validate its function and to begin to establish its role as a possible screening test for macular pathologies. We report our first results on using carotenoid Raman detection in imaging mode. The results on retinal Raman imaging reveal highly specific and quantitative information regarding the spatial distribution of macular pigments. We also compare Raman technology with others availabe today subjective and objective MP detection methods and show that Raman spectroscopic technology has tremendous potential as a breakthrough method for rapid screening of carotenoid antioxidant levels in large populations that are at risk for vision loss from age-related macular degeneration, the leading cause of blindness of the elderly in the developed world.

Retinopathy of Prematurity (ROP) denotes a patholgoic development of the retina in prematurely born children. In order to prevent severe permanent damage to the eye and enable a timely treatment, the fundus of the eye in such children has to be examined according to established procedures. By the way of a miniaturized fundus camera it is intended to record digital pictures of the fundus for on-line or off-line examination and diagnosis. Within the framework of a network for telescreening of ROP, this communication is devoted to technical aspects related to the development of a miniaturized, handheld fundus camera that can be used to relate digital images of the fundus covering the entire area of interest to the network. The images can then be examined by a specialist who is, if not available on location, remote from the hospital. Due to the limited amount of space in a neonatology unit, furthermore, electronic racks containing controllers, computers, etc. are not acceptable, i.e., miniaturization and integration of all functions associated with networking is necessary.

The effectiveness of image stabilization with a retinal tracker in a multi-function, compact scanning laser ophthalmoscope (TSLO) was demonstrated in initial human subject tests. The retinal tracking system uses a confocal reflectometer with a closed loop optical servo system to lock onto features in the fundus. The system is modular to allow configuration for many research and clinical applications, including hyperspectral imaging, multifocal electroretinography (MFERG), perimetry, quantification of macular and photo-pigmentation, imaging of neovascularization and other subretinal structures (drusen, hyper-, and hypo-pigmentation), and endogenous fluorescence imaging. Optical hardware features include dual wavelength imaging and detection, integrated monochromator, higher-order motion control, and a stimulus source. The system software consists of a real-time feedback control algorithm and a user interface. Software enhancements include automatic bias correction, asymmetric feature tracking, image averaging, automatic track re-lock, and acquisition and logging of uncompressed images and video files. Normal adult subjects were tested without mydriasis to optimize the tracking instrumentation and to characterize imaging performance. The retinal tracking system achieves a bandwidth of greater than 1 kHz, which permits tracking at rates that greatly exceed the maximum rate of motion of the human eye. The TSLO stabilized images in all test subjects during ordinary saccades up to 500 °/sec with an inter-frame accuracy better than 0.05 °. Feature lock was maintained for minutes despite subject eye blinking. Successful frame averaging allowed image acquisition with decreased noise in low-light applications. The retinal tracking system significantly enhances the imaging capabilities of the scanning laser ophthalmoscope.

We have expanded our efforts to generate high spatial resolution images showing the distibution 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 filtered 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 significnt differences among subjects, both in regard to absolute levels ss well as spatial distribution within the macula. Since the light levels used to obtain these images are well below established ssafety limits, this technique holds promise for developing a rapid screening diagnostic in large populations at risk for vision loss from age-realted macular degeneration.

The method of so-called laser interferometric chromoretinometry based on the use of laser sources with different colors of light in retinometer is considered. The results of application of this method for determination of retinal visual acuity (RVA) at various diseases of eye and for diagnostics of the earliest age pathological changes of a crystalline lens are discussed. Transformation of scatterers structure in the eye at age pathological changes of a crystalline lens results in essential changes in scattering of light angular spectra. Intensity of the scattered light depends on the wavelength, hence, the decrease of contrast of intererence fringes for different wavelengths is different. The dependence of fringe contrast on the wavelength can be used for in vivo diagnostics of crystalline lens pathology.

The new optical system for interference determination of retinal visual acuity (RVA) based on the use special diffraction elements random phase screens with two identical microstructures is offered. The system includes low coherence sources with quasi-monochromatic red, green, and blue light colors and special diffraction optical element that creates on patient retina an interference pattern with parallel fringes of a particular color. The restuls of the system application in diagnostics of the earliest age patholgocal changes of the lens of eye are discussed. 42 patients (74 eyes) with the initial shapes of cataract and control group without pathology are surveyed. It is established, that at the patients with initial shapes of cataract the values of RVA by green and dark blue colors are lower than it by red, and at the patients without pathology these values coincide. Intensity of scattering light depends on the wavelength, and the interference pattern contrast at the presence of lens inhomogeneities is variable for different wavelengths. Hence, the given system can be used for diagnostics of the earliest age pathological changes in a lens.

Based on eye movement data, we present a study on the effect of various laser and eye-tracking parameters on the optical outcome after scanning spot refractive surgery. Numerical simulations of the entire ablation process were performed on a schematic model eye under variation of the following parameters: ablation depth per pulse, laser spot size, eye tracker latency and magnitude of refractive correction. Three-dimensional ray tracing through an analytical model eye featuring the ablated corneal front surface enabled evaluation of the resulting optical quality. The modulation transfer function (MTF) was calculated to rate the difference in optical quality between an ideal (movement-free) treatment, and treatments performed with an eye-tracker working with a certain latency. For all the calculations it was assumed, that the laser repetition rate remains constant at 250 Hz. It was shown, that the contrast transfer can decrease significantly with increasing latency of the eye-tracker. For constant laser and tracking parameters, this decrease was found to be more significant for higher myopic corrections. It was further shown, that treatments performed with smaller spot sizes and smaller ablation depths per pulse are more sensitive to tracking latency. Assuming a certain eye tracker latency, the most stable results are obtained for large beam diameters and high central ablation depths per pulse. Latencies below 10 ms would allow for a reduction of the beam diameter to 0.50 mm as well as for ablation depths as small as 0.50 microns.