Contrast sensitivity function (CSF) measures the overall sensitivity of the visual system from the retina to the visual cortex. There are numerous diseases, clinical and physiological conditions as well as aging processes that can influence the CSF. METHODS: The 22 subjects (8 male and 14 females) ranging in age from 19 to 75 years that participated in the study were divided into two groups - below and above 50 years of age. The older patients were all pseudophakic. All subjects underwent complete eye examination and were refracted and corrected for the trial's working distance of 1.5 meter. Scotopic CSF was tested monocularly after 3 minutes of dark adaptation by a computerized method using Gabor patches as targets with spatial frequencies between 1.5-6 cycles per degree (cpd). The test was conducted in a completely darkened room, with the monitor covered with neutral density filters having a luminance of 0.35 cd/m². RESULTS: The mean CSF for the older age group was 11.6, 10.3, 5.5, 2.9 for 1.5, 2.25, 3, 6 cpd respectively while the mean CSF for the younger age was 20.7, 9.8, 3.8, for the frequencies of 1.5, 3, 6 cpd respectively. Univariant analysis had found the association between CSF and both age group and spatial frequencies to be statistically significant (p=0.027, p<0.001 for age group and spatial frequency, respectively). A fair negative correlation between age and the dark-adapted contrast sensitivity was calculated (correlation coefficient=-0.35, p=0.004, adjusted for spatial frequency). CONCLUSION: CSF under nearly scotopic conditions declines with age, a decline that can only partially explained by preneuronal factors. In both age groups the CSF declines with increasing spatial frequency. In most of the older subjects the 6 cpd Gabor patches were too difficult to detect. This selective CSF loss may reflect either reduction in cone spacing, or decreased efficiency of neural processing from the fovea to the cortex. The fact that the younger subjects are sensitive to the higher spatial frequencies and the fact that the test was performed only after 3 minutes of adaptation, support our assumption that we are measuring a foveal function. The simplicity, duration and personal computer compatibility make the procedure practical and readily available for use in clinical settings.

In the area of ophthalmic refractive surgery research, the Zernike expansion of the Wavefront aberrations has been the key factor in the measurement, representation and evaluation of the human eye aberrations in many different clinical situations. The Wavefront Aberrations described by the Zernike expansion can be translated as the polynomial expansion of the exit pupil of an optical system that represents the total Wavefront aberrations (corneal + internal elements) of the eye. In this direction, we can use this exit pupil to calculate both the incoherent Point Spread Function (PSF) and the Optical Transfer Function (OTF) of this system. With either of these two functions (PSF or OTF), we can easily calculate the output image of a certain object. This information can be used to evaluate the visual performance of the eyes with a set of pre-determined objects and their corresponding images. We apply these results to characterize the behavior of the aberrations of human eyes that in principle do not need any type of refractive compensation or correction, in order to have a reference which may be ethnical-dependent. We are interested in describing the set of aberration characterizing the Normal Mexican Eye (NME). To achieve our goal, we start our study with a group of Mexican Males with an Uncorrected Visual Acuity (UCVA) of 20/20, 20/30, and 20/40. We present the preliminary results of our characterization.

Purpose: To non-invasively measure the thickness of the anterior and posterior lens capsule, and to determine if it significantly changes during accommodation. Methods: Anterior and posterior capsule thickness was measured on post-mortem lenses using a non-contact optical system using a focus-detection technique. The optical system uses a 670nm laser beam delivered to a single-mode fiber coupler. The output of the fiber coupler is focused on the tissue surface using an aspheric lens (NA=0.68) mounted on a translation stage with a motorized actuator. Light reflected from the sample surface is collected by the fiber coupler and sent to a photoreceiver connected to a computer-controlled data acquisition system. Optical intensity peaks are detected when the aspheric lens is focused on the capsule boundaries. The capsule thickness is equal to the distance traveled between two peaks multiplied by the capsule refractive index. Anterior and posterior lens capsule thickness measurements were performed on 18 cynomolgus (age average: 6±1 years, range: 4-7 years) eyes, 1 rhesus (age: 2 years) eye, and 12 human (age average: 65±16, range: 47-92) eyes during simulated accommodation. The mounted sample was placed under the focusing objective of the optical system so that the light was incident on the center pole. Measurements were taken of the anterior lens capsule in the unstretched and the stretched 5mm states. The lens was flipped, and the same procedure was performed for the posterior lens capsule. Results: The precision of the optical system was determined to be ±0.5um. The resolution is 4um and the sensitivity is 52dB. The human anterior lens capsule thickness was 6.0±1.2um unstretched and 4.9±0.9um stretched (p=0.008). The human posterior lens capsule was 5.7±1.2um unstretched and 5.7±1.4um stretched (p=0.974). The monkey anterior lens capsule thickness was 5.9±1.9um unstretched and 4.8±1.0um stretched (p=0.002). The monkey posterior lens capsule was 5.9±2.0um unstretched and 5.1±1.3um stretched (p=0.128). Conclusions: The results indicate that the primate anterior lens capsule thickness changes during accommodation.

Purpose: To design and test an optical system to measure the optical quality of post mortem lenses during simulated accommodation. Methods: An optical bench top system was designed to measure the point spread function and calculate the modulation transfer function (MTF) of monkey and human ex-vivo crystalline lenses. The system consists of a super luminescent diode emitting at 850nm, collimated into a 3mm beam which is focused by the ex-vivo lens under test. The intensity distribution at the focus (point spread function) is re-imaged and magnified onto a beam profiler CCD camera. The optical quality in terms of spatial frequency response (modulation transfer function) is calculated by Fourier transform of the point spread function. The system was used on ex-vivo lenses with attached zonules, ciliary body and sclera. The sclera was glued to 8 separate PMMA segments and stretched radial by 5mm on an accommodation simulating lens stretching device. The point spread function was measured for each lens in the relaxed and stretched state for 5 human (ages 38-86 years) and 5 cynomolgus monkey (ages 53 - 67 months) fresh post mortem crystalline lenses. Results: Stretching induced measurable changes in the MTF. The cutoff frequency increased from 54.4±13.6 lp/mm unstretched to 59.5±21.4 lp/mm stretched in the post-presbyopic human and from 51.9±24.7 lp/mm unstretched to 57.7±18.5 lp/mm stretched cynomolgus monkey lenses. Conclusion: The results demonstrate the feasibility of measuring the optical quality of ex-vivo human and cynomolgus monkey lenses during simulated accommodation. Additional experiments are underway to quantify changes in optical quality induced by stretching.

We have designed, developed, and tested a three-dimensional tracking and imaging system that uses a novel optical layout to acquire both en-face confocal images by scanning laser imaging (e.g. scanning laser ophthalmoscopy, SLO) and high-resolution depth sections by optical coherence tomography (OCT). The present application for this system is retinal imaging. The instrument is capable of sequentially collecting OCT and SLO images with the simple articulation of an optic affixed to a flip-mount. In addition, we have extended our mature transverse tracking system for full three-dimensional motion stabilization. The tracking component employs an innovative optical and electronic design that encodes transverse and depth tracking information on a single beam. We have demonstrated en face SLO imaging with a resolution of ~25 μm and depth-resolved OCT imaging with a resolution of ~10 μm. On artificial targets, transverse tracking was robust up to 1 m/s with a bandwidth of ~1 kHz and depth tracking was robust up to a velocity of ~15 cm/sec, a range of ~1 mm, and a bandwidth of a few hundred Hz. The details of the instrument, including optical and electronic design, are discussed. The system has the potential to provide clinicians and researchers with a wide variety of diagnostic information for the early detection and treatment of retinal diseases.

We built a Fourier domain optical coherence tomography (FD-OCT) system using a line scan CCD camera that allows real time data display and acquisition. This instrument is able to produce 2D B-scans as well as 3D data sets with human subjects in vivo in clinical settings. In this paper we analyze the influence of varying exposure times of the CCD detector on image quality. Sensitivity values derived from theoretical predictions have been compared with measurements (obtained with mirrors and neutral density filters placed in both interferometer arms). The results of these experiments, discussion about differences between sensitivity values, potential sources of discrepancies, and recommendations for optimal exposure times will be described in this paper. A short discussion of observed artifacts as well as possible ways to remove them is presented. The influence of relative retinal position with respect to reference mirror position will also be described.

This purpose of this study is to demonstrate the feasibility of using multiphoton microscopy in ophthalmologic imaging. Without the introduction of extrinsic fluorescence molecules, multiphoton induced autofluorescence and second harmonic generation signals can be used to obtain useful structural information of normal and diseased corneas. Our work can potentially lead to the in vivo application of multiphoton microscopy in investigating corneal physiology and pathologies.

The newest generation of confocal scanning laser ophthalmoscopes with adaptive optics correction of ocular aberrations provides retinal images of unprecedented resolution, allowing for real-time imaging of photoreceptors in the living human eye. Natural fixational eye movements made by the subject/patient during recording produce distortions that are unique in each frame. Correction for these distortions is necessary before multiple frames can be added together to achieve noise reduction or to build a mosaic image from different retinal areas. Here we describe the characteristics of fixational eye movements and the distortions they produce during retinal imaging, we show examples of images with particular distortions, and show eye movement records obtained during the correction of these distortions.

PURPOSE: To assess accuracy and reproducibility of retinal vessels caliber measurement in Heidelberg retina tomographer (HRT II) images by new developed method. METHODS: 76 images of optic nerve head were obtained from 76 eyes. Eight vessels' diameters were measured in each case in the area of 0.5 to 1.0 disc diameter from the optic disc margin. The window for "interactive measurements" was used to determine three-dimensional coordinates (x,y,z) of each vessel diameter. Diameter of each vessel was calculated according to the Pythagorean Theorem (value of "z" coordinate remained unchanged). RESULTS: Diameter of retinal arterioles varied from 55,0 to 106,5 μm. Diameter of retinal venulas ranged from 68,9 to 140,1 μm. The standard deviation value changed from 0,6 to 16 micron. Artetiole/venule ratio mean value was 0,702±0,039. CONCLUSIONS: Measurement of retinal vessels diameter in images obtained during retinal tomography is exact and informative. The described method is the unique way of retinal vessels caliber measurement in absolute values.

In this study we show clinical application of Spectral Optical Coherence Tomography (SOCT), which enables operation with 40 times higher speed than commercial Stratus OCT instrument. Using high speed SOCT instrument it is possible to collect more information and increase the quality of reconstructed cross-sectional retinal images. Two generations of compact and portable clinical SOCT instruments were constructed in Medical Physics Group at Nicolaus Copernicus University in Poland. The first SOCT instrument is a low-cost system operating with standard, 12 micrometer axial resolution and the second is high resolution system using combined superluminescent diodes light source, which enables imaging with 4.8 micrometer axial resolution. Both instruments have worked in Ophthalmology Clinic of Collegium Medicum in Bydgoszcz. During the study we have examined 44 patients with different pathologies of the retina including: Central Serous Chorioretinopathy (CSC), Choroidal Neovascularization (CNV), Pigment Epithelial Detachment (PED), Macular Hole, Epiretinal Membrane, Outer Retinal Infarction etc. All these pathologies were first diagnosed by classical methods (like fundus camera imaging and angiography) and then examined with the aid of SOCT system. In this contribution we present examples of SOCT cross-sectional retinal imaging of pathologic eyes measured with standard resolution. We also compare cross-sectional images of pathology obtained by standard and high resolution systems.

We present images of ocular tissues obtained using ultrahigh resolution full-field OCT. The experimental setup is based on the Linnik interferometer, illuminated by a tungsten halogen lamp. En face tomographic images are obtained in real-time without scanning by computing the difference of two phase-opposed interferometric images recorded by a high-resolution CCD camera. A spatial resolution of 0.7 μm × 0.9 μm (axial × transverse) is achieved thanks to the short source coherence length and the use of high numerical aperture microscope objectives. A detection sensitivity of 90 dB is obtained by means of image averaging and pixel binning. Whole unfixed eyes and unstained tissue samples (cornea, lens, retina, choroid and sclera) of ex vivo rat, mouse, rabbit and porcine ocular tissues were examined. The unprecedented resolution of our instrument allows cellular-level resolution in the cornea and retina, and visualization of individual fibers in the lens. Transcorneal lens imaging was possible in all animals, and in albino animals, transscleral retinal imaging was achieved. We also introduce our rapid acquisition full-field optical coherence tomography system designed to accommodate in vivo ophthalmologic imaging. The variations on the original system technology include the introduction of a xenon arc lamp as source, and rapid image acquisition performed by a high-speed CMOS camera, reducing acquisition time to 5 ms per frame.

We present clinical data obtained with the aid of a novel instrumentation using, high speed, ultrahigh resolution Spectral/Fourier domain Optical Coherence Tomography (SOCT). This method allows performing video rate, ultrahigh resolution cross-sectional images with 98 dB of sensitivity, 100 times faster that previously reported UHR OCT system with comparable axial resolution of 3 um. Ultrahigh resolution imaging enables improved visualization of retinal architectural morphology compared to standard resolution OCT. High speed, ultrahigh resolution OCT using Spectral/Fourier domain detection promises to significantly enhance the utility of OCT for clinical applications. High speed imaging enables high density data sets to be acquired which can increase the quality of reconstructed cross-sectional images and can help to visualize small focal pathologic changes. This technique helps reconstructing true retinal topography without motion artifacts. Submitted manuscript describes the technology, its clinical performance and present preliminary data obtained for various retinal pathologies.

Ultrahigh resolution OCT using broadband light sources achieves improved axial image resolutions of ~2-3 um compared to standard 10 um resolution OCT used in current commercial instruments. High-speed OCT using Fourier/spectral domain detection enables dramatic increases in imaging speeds. 3D OCT retinal imaging is performed in human subjects using high-speed, ultrahigh resolution OCT, and the concept of an OCT fundus image is introduced. Three-dimensional data and high quality cross-sectional images of retinal pathologies are presented. These results show that 3D OCT may be used to improve coverage of the retina, precision of cross-sectional image registration, quality of cross-sectional images, and visualization of subtle changes in retinal topography. 3D OCT imaging and mapping promise to help elucidate the structural changes associated with retinal disease as well as to improve early diagnosis and monitoring of disease progression and response to treatment.

Form-birefringent properties of the retinal nerve fiber layer (RNFL) have become increasingly important as investigators strive to provide an improved methodology for glaucoma diagnosis. Techniques such as scanning laser polarimetry (SLP) and polarization-sensitive optical coherence tomography (PS-OCT) are two approaches which directly assess RNFL neurotubules, the sub-cellular structures responsible for form-birefringence and axoplasmic transport in retinal ganglion cell axons. We present a novel algorithm for enhancing the sensitivity of PS-OCT. Enhanced polarization-sensitive OCT (EPS-OCT) is capable of detecting small transformations in polarization typically experienced by light propagating through the thin and weakly birefringent primate RNFL. We report birefringence and nerve fiber orientation measurements for the peripapillary region in healthy in vivo primate RNFL and discuss the implications of the enhanced-sensitivity approach on noninvasive quantification of form-birefringence in glaucoma diagnostics.

New analysis tools to address the problem of early detection of the eye blinding disease glaucoma are presented. The thickness maps of the Retinal Nerve Fiber Layer (RNFL) corresponding to 184 eyes (92 Normal and 92 Glaucoma Patients) were obtained from a Scanning Laser Polarimeter (Gdx-VCC). The two dimensional data was used to draw features as opposed to the circular band one-dimensional data in previous approaches. Fourier analysis was performed on the 90° projection of the thickness map data to emphasize the shape contained in the RNFL. Different parameters from the Fourier Coefficients were drawn and tested for their ability to detect glaucoma. Significant differences were found in the shape measures of the projections and the ROC curve analysis was done to measure the separability of the sample set with those features. Another approach was to analyze the shape of the entire 2 dimensional thickness map through a 2D Fourier Transform. A circular ring band (10 pixel wide) data at a radius of 20 pixels was analyzed for this 2D FT. Principal Component Analysis was performed on this data for dimension reduction of feature space. Finally Fisher's linear discriminant function (LDF) was used as a classifier. The evaluation of different parameters obtained through the Fourier analysis of the thickness map image of RNFL was found to be a useful tool as an analysis strategy for glaucoma detection.

We report on the development of a new polarization sensitive OCT (PS-OCT) system and its application to measure and image the polarizing properties of the human retina in vivo. Contrary to conventional OCT, the system is not based on A-scans but on transverse scanning of the measurement beam across the retina. A highly precise carrier frequency is generated by acousto-optic modulators. A two-channel polarization sensitive detection unit is used to obtain amplitude and phase of the interference signals in two orthogonal channels. This allows to measure and image three parameters simultaneously: reflectivity, retardation, and birefringent axis orientation. The instrument can be operated in different ways: 2D imaging along x-z or y-z planes (B-scans), along the x-y plane (C-scan), and 3D imaging are possible. In vivo PS-OCT images were recorded in the fovea and nerve head region of healthy volunteers. In the region of the fovea, the birefringence of Henle's fiber layer could be measured; furthermore, a depolarizing layer at the RPE-choriocapillaris complex was discovered. In the region of the nerve head, birefringence and orientation of the fibers of the RNFL could be imaged.

Adaptive optics (AO) is becoming increasingly important in improving system resolution in flood illuminated fundus cameras, confocal laser scanning ophthalmoscopes (cSLO) and optical coherence tomography (OCT). For the latter two cases, AO also provides an increase in the throughput light levels. The flood and cSLO modalities have allowed for the routine, in-vivo visualization of individual cone photoreceptor cells and real time blood flow measurements of single leukocyte cells. Most recently, evidence of the rod mosaic has also been observed. A key component in all of these systems is the deformable mirror (DM) that provides the correction of the high order aberrations. The majority of these systems to-date have utilized large, expensive DMs originally designed for astronomy. This paper details ongoing work at Iris AO, Inc in which advanced fabrication techniques based on microelectromechanical systems (MEMS) are being leveraged. This approach yields extremely compact DMs that offer higher performance and lower cost, coupled with the ability for batch fabrication. The Iris AO design uses an array of individually addressable hexagonal segments than can each be moved in three orthogonal directions. Such a design allows for superior ocular wavefront fitting performance and very high stroke (>10 microns). Additionally, our DMs can be fabricated with diameters that are an order of magnitude smaller than conventional non-MEMS techniques.

The wave front corrector is one of the three key elements in adaptive optics, along with the wave front sensor and the control computer. Low cost, compact deformable mirrors are increasingly available. We have tested the AOptix bimorph deformable mirror, originally developed for ultra-high bandwidth laser communication systems, to determine its suitability for vision science applications, where cornea and lens introduce optical aberrations. Measurements of the dynamic response of the mirror to a step input were obtained using a commercial Laser Doppler Vibrometer (LDV). A computer-controlled Twyman-Green interferometer was constructed to allow the surface height of the deformable mirror to be measured using Phase-Shifting Interferometry as a function of various control voltages. A simple open-loop control method was used to compute the control voltages required to generate aberration mode shapes described by the Zernike polynomials. Using this method, the ability of the deformable mirror to generate each mode shape was characterized by measuring the maximum amplitude and RMS error of each Zernike mode shape up to the fifth radial order. The maximum deformation amplitude was found to diminish with the square of the radial order of the Zernike mode, with a measured deformation of 8 microns and 1.5 microns achieved at the second-order and fifth-order Zernike modes, respectively. This deformation amplitude appears to be sufficient to allow the mirror to correct for aberrations up to the fifth order in the human eye.

Aim: The objective of this project was to evaluate high resolution images from an adaptive optics retinal imager through comparisons with standard film-based and standard digital fundus imagers. Methods: A clinical prototype adaptive optics fundus imager (AOFI) was used to collect retinal images from subjects with various forms of retinopathy to determine whether improved visibility into the disease could be provided to the clinician. The AOFI achieves low-order correction of aberrations through a closed-loop wavefront sensor and an adaptive optics system. The remaining high-order aberrations are removed by direct deconvolution using the point spread function (PSF) or by blind deconvolution when the PSF is not available. An ophthalmologist compared the AOFI images with standard fundus images and provided a clinical evaluation of all the modalities and processing techniques. All images were also analyzed using a quantitative image quality index. Results: This system has been tested on three human subjects (one normal and two with retinopathy). In the diabetic patient vascular abnormalities were detected with the AOFI that cannot be resolved with the standard fundus camera. Very small features, such as the fine vascular structures on the optic disc and the individual nerve fiber bundles are easily resolved by the AOFI. Conclusion: This project demonstrated that adaptive optic images have great potential in providing clinically significant detail of anatomical and pathological structures to the ophthalmologist.

We have developed a simulator for virtual phacoemulsification surgery. In the current study, the performance of one experienced cataract surgeon was compared to the performance of four subjects naive to cataract surgery. They all operated on the same virtual patient and a number of different response variables were measured. It was found that the experienced subject performed better than the naive subjects on almost all response variables. This indicates that the simulator developed by us is authentic for phaco emulsification surgery. The lack of negative effects in case of complications during virtual phacoemulsification surgery makes the phaco simulator that we developed a very attractive tool for learning phacoemulsification surgery.

Purpose: To determine the attenuation of free electron laser (FEL) energy at several wavelengths through microscope objective and eyeglass lenses. Materials and Methods: The FEL at wavelengths of 2.3 um, 2.5 um, 3.0 um, 3.5 um, 4.0 um, 4.5 um, 5.0 um, 6.45 um, 7.0 um, 7.5 um, and 8.0 um was telescoped using a 500 mm nominal focal length lens and a 200 mm focal length lens. The beam had a final spot of about 3 mm and was passed through a 3 mm aperture and onto the 8 mm active area of a J9LP Molectron detector. The eyeglass sample was placed 3 cm in front of the detector. Energy readings were averaged over multiple pulses. Results: Attenuation varied greatly with wavelength and sample from a low attenuation of 0.46 dB, 90% transmission, for short wavelengths through common glass to greater than 60 dB attenuation (transmission at the detector noise level) for IR safe glass by Aura, Inc. Conclusion: Only the designated laser safety goggles effectively attenuate free electron laser energy at 2.3 um and 2.5 um. A microscope objective lens, polycarbonate, and silica glass eyewear is capable of effectively attenuating FEL energy at wavelengths greater than 4.5 um, but the polycarbonate lenses demonstrated material damage.

The Mark-III Free Electron Laser (FEL), tuned to λ=6.45 μm has been demonstrated to provide for efficient ablation in ocular and neural tissues with minimal collateral damage. To date, the role of the FEL pulse structure on the mechanism of ablation has not been determined. In an effort to study the role of the FEL micropulse on the ablation of corneal tissue, the native pulse structure of the FEL, a 2.85 gigahertz repetition of picosecond pulses within a five microsecond macropulse envelope, was changed using a a pulse stretcher. This device changes the duration of the micropulse from 1 picosecond to 30-200 picoseconds in length, thus reducing the peak intensity of the micropulse by as much as 200x the original intensity, while the macropulse energy remains unchanged. Two basic metrics were studied: the ablation threshold on water and the ablation crater depth on gelatin. These metrics were employed at λ=6.45 and 6.1 μm for 1, 100, and 200 picoseconds in micropulse duration. The results showed a very slight difference between the 1, 100, and 200 picosecond micropulse duration, given a 200 fold decrease in peak energy for both the threshold and crater depth measurements. Brightfield imaging was also performed to probe the ablation dynamics and showed no difference between the 1 and 200 ps micropulses. The effect of changing the micropulse duration was studied on the ablation of canine cornea. Craters (500 micron diameter) were created with 25 pulses at three times the ablation threshold as determined for water on freshly enucleated corneas within 12 hours of removal. Three rows of seven craters were created on the center of each cornea. The native one picosecond micropulse and 200 picosecond stretched micropulse were compared at λ=6.1 and 6.45 μm. Histological data shows that less thermal damage is present at 6.1 μm compared with 6.45 μm; however, there is no significant difference between the native and stretched pulses with respect to thermal damage.

Fast and non-invasive detection of cellular stress is useful for fundamental research and practical applications in medicine and biology. Using Light Scattering Spectroscopy we extract information about changes in refractive index and size of the cellular organelles. Particle sizes down to 50nm in diameter can be detected using light within the spectral range of 450-850 nm. We monitor the heat-induced sub-cellular structural changes in human RPE cells and, for comparison, in transfected NIH-3T3 cells which express luciferase linked to the heat shock protein (HSP). Using inverse light scattering fitting algorithm, we reconstruct the size distribution of the sub-micron organelles from the light scattering spectrum. The most significant (up to 70%) and rapid (20sec) temperature-related changes can be linked to an increase of refractive index of the 160nm sized mitochondria. The start of this effect coincides with the onset of HSP expression. This technique provides an insight into metabolic processes within organelles larger than 50nm without exogenous staining and opens doors for non-invasive real-time assessment of cellular stress, which can be used for monitoring of retinal laser treatments like transpupillary thermo therapy or PDT.

The aim of this study is to explore the possibility of correlating the temporal fluctuations of scattered light intensity from the chorioretinal tissue during Transpupillary Thermotherapy and the temperature of the irradiated tissue. The chorioretinal tissue is a mixture of macromolecules that either are rigidly fixed into a structural matrix or can move. The possible motions are induced by the blood flow and by the temperature. Therefore, by analyzing the scattered intensity fluctuations induced by the molecules motion, the retinal tissue temperature can be recovered. In this paper, we present the theory supporting this idea and the results of a preliminary experimental activity performed on enucleated bovine eyes.

It has been already demonstrated that electrical stimulation of retina can produce visual percepts in blind patients suffering from macular degeneration and retinitis pigmentosa. Current retinal implants provide very low resolution (just a few electrodes), while several thousand pixels are required for functional restoration of sight. We present a design of the optoelectronic retinal prosthetic system that can activate a retinal stimulating array with pixel density up to 2,500 pix/mm² (geometrically corresponding to a visual acuity of 20/80), and allows for natural eye scanning rather than scanning with a head-mounted camera. The system operates similarly to "virtual reality" imaging devices used in military and medical applications. An image from a video camera is projected by a goggle-mounted infrared LED-LCD display onto the retina, activating an array of powered photodiodes in the retinal implant. Such a system provides a broad field of vision by allowing for natural eye scanning. The goggles are transparent to visible light, thus allowing for simultaneous utilization of remaining natural vision along with prosthetic stimulation. Optical control of the implant allows for simple adjustment of image processing algorithms and for learning. A major prerequisite for high resolution stimulation is the proximity of neural cells to the stimulation sites. This can be achieved with sub-retinal implants constructed in a manner that directs migration of retinal cells to target areas. Two basic implant geometries are described: perforated membranes and protruding electrode arrays. Possibility of the tactile neural stimulation is also examined.

Iontophoresis (IONT) is a non-invasive technique in which a low electric current is used to enhance the penetration of charged molecules into tissue. This technique has been used in various fields of medicine, mostly in transdermal drug delivery. This study was aimed to evaluate the efficacy and the distribution profile of gentamicin using corneal IONT on infected and healthy rabbit eyes. Corneal iontophoresis of gentamicin sulfate was studied using drug-loaded disposable hydrogel probes mounted on a portable iontophoretic device, applying a low current for 60 seconds. This study confirmed that a triple iontophoretic treatment of gentamicin for only 60 seconds (0.5mA) significantly reduces the count of pseudomonas in the infected cornea to a non-infectious level. Peak gentamicin concentrations at the healthy corneas (363.1 ± 127.3 μg/g) and at the aqueous humor (29.4 ± 17.4 μg/ml) were reached immediately and two hours after a single iontophoretic treatment, respectively. The concentration versus time profile of gentamicin following iontophoresis revealed a gentamicin half life of 2.07 h in the anterior chamber, and a clearance of 1.73 μl/min from the anterior chamber to the posterior segments of the eye. This study indicates that a short iontophoretic treatment using gentamicin-loaded hydrogels has a potential clinical value in treating corneal infections, by increasing drug penetration to the eye and maintaining therapeutic levels for more than eight hours.

The ex vivo accommodation simulator stretches crystalline lenses radially under controlled conditions, while monitoring the changes in zonular tension and lens diameter. A dual coaxial laser beam system was added for measuring changes in optical power as the lens is stretched. The EVAS instrument was fully characterized and calibrated. The results from 3 porcine eyes will be presented. Several crystalline lenses, similar in shape and size to porcine lenses, were cast molded in silicone gels of different stiffness. These lenses were evaluated using the EVAS instrument and custom made lens holding fixtures. With their well defined shape and material properties, results from these measurements will be useful for cross-validation of finite element models.

Purpose: To evaluate the feasibility to induce lens epithelial cell death with intraoperative hyperthermia for prevention of secondary cataract. Methods: A prototype miniature resistive hyperthermia probe was designed. The probe contained a thermocouple for temperature feed-back. A timer allowed monitoring of the electrical driving of the hyperthermia probe and the temperature induced as a function of time. To model the heating response, a simple model of the lens capsule was constructed using a thin acrylic plastic shell embedded in a sponge immersed in a water bath at 37°C. The shell was filled with sodium hyaluronate. The probe was positioned at the center of the shell with the thermocouple next to the wall. An experimental protocol was developed to assess the feasibility of increasing the temperature of the human lens to hyperthermia levels in fresh cadaver eyes: An annular metal ring was bonded just below the limbus, the cornea and iris were sectioned, the lens material was removed through a central 5mm diameter capsulorhexis, the capsule was filled with SHA and the globe was set on a temperature-controlled cylindrical vial. Preliminary Results: At 3.3W (2.2V, 1.5A) the shell's content increases from 37°C to 51°C in 30s. At that temperature, LEC death is expected to occur within 1sec. Conclusion: This preliminary study demonstrates the feasibility of increasing the temperature of the capsular bag to kill LECs by hyperthermia.

The dot patterned hydrophilic and hydrophobic groups were photo-chemically substituted in minute pattern on the polymethylmethacrylate [PMMA] intraocular lens [IOL] by the Xe₂ excimer lamp and the ArF excimer laser; consequently, the IOL that is free from fibrin has been developed. PMMA has been used as an intraocular lens IOL because of its high transmittance in the visible region and superb mechanical modifiability. However, protein and fat are stuck onto the lens surface after a long-term insertion, where cells proliferate; which causes the surface to get opaque, namely after-cataract. Firstly, the IOL was irradiated with Xe₂ excimer lamp in the presence of perfluoropolyether [PFPE] to be hydrophobic. By the photochemical reaction, the CF₃ functional groups were substituted on the IOL surface. In order to substitute hydrophilic groups in matrix-form on the surface, the ArF laser light was then irradiated on the hydrophobic surface in the presence of water through the 50mm f dot-patterned negative mask and the lens to project the reduced pattern. With this selective photochemical surface modification, the hydrophilic and hydrophobic groups were arrayed alternately on the sample surface. The modified IOL was soaked in fibrin [FIB] water solution, and the fibrin-sticking rate was measured by infrared spectroscopy [FT-IR]. The lower fibrin-sticking rate of the IOL surface was achieved by the hydrophobic and hydrophilic micro domain structures. Furthermore, it was confirmed that the fibrin-sticking rate decreased as the OH group interval was narrowed. The modified surface with the 20 mm f domains with hydrophilic and hydrophobic was lowest in fibrin sticking.

Ultrashort laser pulses are increasingly used in refractive eye surgery to cut inside transparent corneal tissue. This is exploited by the fs-LASIK procedure which affords the opportunity to correct ametropia without any mechanical effects. The cutting process is caused by the optical breakdown occurring in the laser focus. During this process only a certain amount of the pulse energy is deposited into the tissue. The remaining pulse energy propagates further through the eye and interacts with the retina and the strong absorbing tissue layers behind. Therefore this investigation shall clarify if the intensity of the remaining laser pulse and the resulting temperature field can damage the retina and the surrounding tissue. Threshold values of the retinal tissue and theoretical calculations of the temperature field will be presented.

According to Helmholtz' theory of accommodation one of the mayor reasons for the development of presbyopia is the increasing sclerosis of the lens. One concept to delay the process of sclerosis or even regain the deformation ability of the lens might be the treatment of the lens by femtosecond laser pulses. Our aim was to evaluate appropriate laser parameters for this possible treatment and to analyse potential changes in deformation ability of the treated lenses. We performed different cutting patterns in enucleated pig lenses (ex vivo) using the disruptive effect of an ultrafast near-infrared laser induced optical breakdown. Pulse energies and spot separation of the laser pulses were varied to investigate the effect on the generated cut. For an evaluation of the gain in deformation ability the lenses were rotated before and after treatment and the changes in lens thickness due to centrifugal forces were measured. In result, a smooth cutting was possible with appropriate parameters. The experiments showed an increase of elasticity in 70% of the eyes. When the lenses were treated more statistically, an average deformation ability increase of nearly 20%, determined by the change of thickness between untreated and treated lens, was measured.

We report on a novel optical method for (i) flap-generation in LASIK procedures as well as (ii) for flap-free intrastromal refractive surgery based on nanojoule femtosecond laser pulses. The near infrared 200 fs pulses for multiphoton ablation have been provided by ultracompact turn-key MHz laser resonators. LASIK flaps and intracorneal cavities have been realized with high precision within living New Zealand rabbits using the system FemtoCutO (JenLab GmbH, Jena, Germany) at 800 nm laser wavelength. Using low-energy sub-2 nJ laser pulses, collateral damage due to photodisruptive and self-focusing effects was avoided. The laser ablation system consists of fast galvoscanners, focusing optics of high numerical aperture as well as a sensitive imaging system and provides also the possibility of 3D multiphoton imaging of fluorescent cellular organelles and SHG signals from collagen. Multiphoton tomography of the cornea was used to determine the exact intratissue beam position and to visualize intraocular post-laser effects. The wound healing process has been investigated up to 90 days after instrastromal laser ablation by histological analysis. Regeneration of damaged collagen structures and the migration of inflammation cells have been detected.

Ortho-K was indicated for sixty eyes of thirty aviators, twenty-one pilots and nine flight attendants, with age of 34.5 on the average. Uncorrected visual acuity (UCVA) was originally 20/30 or worse in all cases. The mean spherical equivalent (SE) was -3.69 Diopters (D). The same ophthalmologist designed full costumed reverse geometry Advanced Orthokeratology lenses for each patient. All the patients were followed at least two years wearing of Advanced Ortho-K lenses. The follow up examinations on auto-refraction, auto-keratometry, uncorrected and corrected visual acuity, intra-ocular pressure, corneal endothelial cells, corneal thickness and curve, and corneal shape were performed in the morning, 10am to 12am. 94% of the patients improved in UCVA up to 20/20 or better, 87% of them improved up to 20/15 or better, and 67% of them improved up to 20/10. The mean SEs improved to -1.90±1.00D during six months, -1.49±1.03D during one year, and -0.73±0.94D during two years. Astigmatism slightly increased by 0.38D on the average, however, it did not cause any serious problems for aviation tasks even during night. Intraocular pressure did not increase and corneal endothelial cells did not decrease. Other ophthalmologic examinations showed normal conditions and any complications were not observed throughout the period. Advanced Ortho-K was evaluated to be safe and effective enough for also aviators with myopia. It can be recommended one of the options of reduction of myopia for aviators. Evaluations on night vision and night glare are planned for further studies.

Ortho-K was indicated for twenty-three eyes of thirteen patients after refractive surgeries such as RK(1) ,PRK(2), and LASIK(3). The average of their Uncorrective Visual Acuity (UCVA) after surgeries was 20/30 or worse, and mean spherical equivalent (SE) was -2.42D. They were followed at least two years wearing of Advanced Ortho-K lenses during night. The following studies were examined on their auto-refraction, auto-keratometry, uncorrected and corrected visual acuity, intra-ocular pressure, corneal endothelium, corneal thickness, corneal curvature, and corneal shape for more than two years. 95% of the patients improved in UCVA up to 20/20 or better, 86% of them improved up to 20/15 or better, and 76% of them improved up to 20/10. The mean SEs improved to -1.20±1.02D during six months, - 1.03±0.83D during one year, and -0.73±0.64D during two years. Astigmatism also slightly decreased. Ophthalmologic examinations showed no abnormalities including flap formation, intra-ocular pressure, and endothelium. Among the refractive surgeries as well as RK and PRK, LASIK has been most popularly spread all over the world. However, patient's quality of vision is not always satisfied during and/or after refractive surgeries, because of several complications such as instability of flap formation, unexpected keratoectasia, diffuse lamellar keratitis, epithelial ingrowth, irregularity of corneal surface which caused myopia regression. In such cases, additional surgical procedures should not be indicated easily. However, Ortho-K is safe and effective enough to correct refractive errors still remained or re-appeared after refractive surgeries. It enables to restore the corneal irregularity to the ideal shape.

Based on experimental data, obtained in vitro from reflectance measurements and in vivo from digital analysis of color images of human irises, melanin content in human and bovine eye irises has been estimated. Reflectance measurements have been performed using commercially available optical multichannel spectrometer LESA-5 (BioSpec, Russia). For registration of color images digital camera Olympus C-5060 has been used. Analysis of the reflectance spectra has been performed by the method used for determination of melanin content in skin. For digital analysis of iris color images, decomposition of the images in RGB-color-coordinate system has been performed. The images have been obtained both from irises of health volunteers as from irises of patients with glaucoma. Original computer program based on Mathcad software has been developed for the analysis. The results obtained from spectral and color measurements have a good agreement each to other. In eye irises of patients with glaucoma, smaller melanin content has been obtained, and the result has been useful for development of novel and optimization of already existing methods of glaucoma diagnostics.

Retinal photocoagulation lesions undergo primary and secondary degeneration followed by partial healing. This study follows the sequential changes in laser-induced retinal lesion over a time span of 60 days. Argon laser lesions were created in 36 pigmented rats. Sections of the retinal lesions were evaluated by light microscopy 1, 24, 48, 72 hours, and 20, and 60 days after the injury (six animals at each time point). The diameter of the lesion was equal to that of the laser spot 1h after irradiation and increased by 24h. It decreased later, slightly during the following 48h and significantly by 20 days. The destruction of photoreceptors was most severe after 24-48h. The nuclei in the outer-nuclear layer were pyknotic at the lesion site at 1h and disappeared later. Healing processes began 72h after the irradiation and was completed by 60 days. Filling-in by sliding of near nuclei was observed by the 60th day. Reversible changes were seen also in the retinal pigment epithelium (with formation of a plaque at 72h and its degradation later on) and in the choroid (disorganization of capillaries by 48h with later reorganization). Conclusions: The development of a laser-induced injury is gradual. The photoreceptors are damaged first and than the damage spreads to other layers of retina and to areas adjacent the primary injury site. The extension of the damage is later stopped and the adjacent tissues tend to fill the lesion and remodel the retina.

The small eye model of the snake permits the imaging of the photoreceptor layer as well as the retinal vasculature and individual blood cells when imaged with a confocal scanning laser ophthalmoscope (CSLO). Snake photoreceptors can be imaged down to their internal mode structure, providing comparison between normal and laser damaged photoreceptor internal mode structure. Moving the CSLO into anterior retina provides imaging of the retinal vasculature and individual blood cell response to acute laser photoreceptor injury. Alteration in individual blood cell activity is readily apparent within seconds post laser exposure, as blood cells cumulate and show charactistic "sticky cell" leukocyte behavior. At energy levels near thermal threshold damage levels, damage down to a single photoreceptor is detectable within 24 hours post exposure with near IR laser imaging sources (780 nm), and visualization of internal mode structure disruption mediated at the outer segment of the photoreceptor. Utilization of in vivo biochemical tags for oxidative stress demonstrates that thermal/mechanical and non-thermal mechanisms of photoreceptor damage can reside in adjacent photoceptors. Preliminary studies with actin based biochemical markers indicate the presence of actin in both the photoreceptor and retinal nerve fiber layer, suggesting the possibility of both active recovery and support processes.

The neuroprotective effect of immunization by glatiramer acetate (Copolymer-1, Cop-1, Copaxone) in adjuvant against laser-induced retinal damage was previously reported. The present study quantitatively compares various regimens of this vaccination for reducing the spread of laser-induced retinal damage and investigates the cellular mechanism of Cop-1 activity. Standard argon laser lesions were created in 78 DA pigmented rats divided into five groups: three Cop-1 single treatment groups (treated 7 days before, immediately after, or 24 hours after the injury), one group treated twice (7 days before and 20 days after injury), and a control group treated with adjuvant 7 days before the injury. The retinal lesions were evaluated 3, 20, and 60 days after the injury. Immunostaining of the retinas of the pretreated and control group animals 3 days after the laser injury was performed for T-cell detection. Cop-1 pre-immunization reduced photoreceptor loss at all time points as measured over the central zone of the lesion and 3 and 20 days after lasing as measured over the whole damaged area. Lesion diameter was reduced only 60 days after laser injury in pre-treated animals. Cop-1 given immediately after injury reduced cell loss as measured 20 and 60 days later in the whole lesion and 20 days after the laser irradiation, when measured in the center of lesion. It had no effect on lesion diameter. Late treatment reduced only the lesion diameter at all time points. Repeated treatment enhanced the neuroprotective effect, decreasing the cell loss in the center of lesion and reducing the diameter of lesion. T-cells were detected in the retinal lesions of pre-immunized animals and not in non-treated group, demonstrating the cellular immune mechanism of Cop-1. Immunization with Cop-1 is neuroprotective against laser-induced retinal injuries, and repeating the treatment enhances this effect. Cellular immune action of Cop-1 of was detected.

Due to the increasing number of optic systems that military personnel are exposed, the development of countermeasures for laser eye injury is of significant concern. Recent reports in the literature suggest some benefit form the use of Light Emitting Diode (LED) therapy on the retina that received a toxic insult. The purpose of this study was to compare retinal cell survival and multifocal electroretinography (mfERG) in a laser retinal injury model following treatment with LED photoillumination. Control and LED array (670 nm) illuminated cynomolgus monkeys received macular Argon laser lesions (514 nm, 130 mW, 100 ms). LED array exposure was accomplished for 4 days for a total dose of 4 J/cm² per day. Baseline and post-laser exposure mfERGs were performed on most of the subjects. Ocular tissues were collected from four animals at Day 4 poast laser exposure and from two animals at 4 months post laser exposure. The tissues were processed for plastic embedding. Retinal cell counts were performed on the lesion sections. Analysis of Variance (ANOVA) results yielded no significant difference in the sparing of photoreceptors, inner nuclear and ganglion cells between the control and LED illuminated subjects. Although pathology showed no significant support for diode therapy, our early mfERG observations previously reported suggested a more rapid functional recovery. Since there is still no uniform therapy for laser retinal injury, research is continuing to determine novel therapies that may provide retinal cell sparing and functional retinal return.

The diagnosis of a laser-induced eye injury occurring in occupational or military environments is often complicated by confounding symptoms, the possibility of pre-existing pathology, and/or a lack of visual deficits that can be clearly associated with a specific incident. Two recent cases are described that illustrate the importance of a thorough differential diagnosis when coexisting retinal pathologies are present with potentially different (e.g. laser or disease) etiologies. Indocyanine green angiography (ICG) and ocular coherence tomography (OCT) used in combination with standard ophthalmic imaging can provide helpful insights as to the etiology of these lesions. Vascular choroidal abnormalities such as hemangiomas or occult histoplasmosis infection can produce findings that can mimic the leakage that may be evident from neovascular membranes associated with laser injury. Further evaluation with OCT and conventional fluorescein angiography (FA) is helpful to look for the classic signature of retinal disruption and retinal pigment layer changes that are often present in association with laser injury. Furthermore, a careful situational assessment of a potential laser exposure is important to confirm the diagnosis of laser-induced eye injury.

Retinal damage induced by mechanical trauma, ischemia or laser photocoagulation increases considerably by secondary degeneration processes. The spread of damage may be ameliorated by neuroprotection that is aimed at reducing the extent of the secondary degeneration and promote healing processes. Hyperbaric oxygen (HBO) treatment consists of inspiration of oxygen at higher than one absolute atmospheric pressure. Improved neural function was observed in patients with acute brain trauma or ischemia treated with HBO. This study was designed to evaluate the neuroprotective effect of hyperbaric oxygen (HBO) on laser induced retinal damage in a rat model. Standard argon laser lesions were created in 25 pigmented rats divided into three groups: Ten rats were treated immediately after the irradiation with HBO three times during the first 24 hr followed by 12 consecutive daily treatments. Five rats received a shorter treatment regimen of 10 consecutive HBO treatments. The control group (10 rats) underwent the laser damage with no additional treatment. The retinal lesions were evaluated 20 days after the injury. All outcome measures were improved by the longer HBO treatment (P<0.01). The shorter HBO treatment was less effective, showing an increase only in nuclei density at the central area of lesion (P< 0.01). Hyperbaric oxygen seems to exert a neuroprotective effect on laser-induced retinal damage in a rat model. In the range of HBO exposures studied, longer exposure provides more neuroprotection. These results encourage further evaluation of the potential therapeutic use of hyperbaric oxygen in diseases and injuries of the retina.

Laser induced retinal damage may involve primary injury to the central retina and secondary damage, including intraretinal scar formation (IRSF) retinal traction (RT) and retinal nerve fiber layer injury (RNFL). We have evaluated these laser induced retinal pathologies with MFERG in non-human primates (NHPs) with a Veris (4.9) MFERG system 103 Hexagons, centered on the macula with non-scaled arrays and in one NHP with a 2-frame/M-step sequence to assess long term exposure effects within the RNFL. Chemical restraint was achieved using Ketamine stability HCL (10 mg/kg IM) and Propofol (0.5 mg-1.2/Kg/min via syringe pump). Peribulbar eye blocks were performed using 2% lidocain or a mixture of 2% Lidocain/Marcain (monitored ocular motility was less than 40 microns in retinal space). Primary and secondary damage effects were induced with either q-switched single pulse Neodymium (1064 nm, 1.0 mJ) or Argon CW (10 to 1000 msec, 10-150 mW). MFERG demonstrated capability to detect primary and secondary induced retinal damage in both 1st and 2nd order kernels. Primary and secondary damage in the central retina was often suppressed in amplitude and with longer latencies relative to the MFERG norm. Preliminary investigations in one NHP with Primary and secondary RNFL damage at 9 to 14 months showed recovery with non-scaled array one frame / M-step sequence but demonstrated significant abnormalities for a two frame/ M-step sequence. Utilization of advanced Veris recording parameters involving spatial and temporal manipulation of the stimulus parameters can improve detection of functional deficits induced by focal laser retinal injury.

The aim of the present study was to characterize permissible exposure limits (MPE) for safety analysis, with an emphasis on the immediate retinal damage, following Nd:YAG Q-switched laser radiation, and to test its correlation to physical parameters. Pigmented rabbits were exposed to Nd:YAG laser radiation (532nm, pulse duration: 20ns) in various energies. Exposures were conducted in retina tissue, very close to the optic nerve, with a total of 20 exposures per retina. Retinas were viewed during the first 10 min following exposure, using an on-line digital video camera. Thereafter, animals were sacrificed for histological evaluation. A part of the retinas were evaluated 24 hours post exposure. A quantitative analysis of the clinical findings, based on a severity score scale and a morphometric analysis of the extent of the lesions, was used to test the statistical relationship with the laser energy and number of pulses. In addition, hemorrhage threshold values were computed using Probit Analysis. Retinal damage, at various levels of severity, was observed immediately after exposure to energies above 10μJ, characterized by edema and subretinal hemorrhages. The appearance and severity of the lesions varied among animals, between fellow eyes and even within the same retina. The relationship between severity and extent of lesions, and energy levels and number of pulses was evaluated. The ED50 for various, immediate types of hemorrhage was determined, and correlated to physical parameters. Histological observations strengthened the clinical findings. The results were discussed in accordance with photomechanical and thermal theories of laser-tissue interactions.

The threshold for laser-induced retinal damage is dependent primarily upon the laser wavelength and the exposure duration. The study of the wavelength dependence of the retinal damage threshold has been greatly enhanced by the availability of tunable lasers. The Optical Parametric Oscillator (OPO), capable of providing useful pulse energy throughout a tuning range from 400 nm to 2200 nm, made it possible to determine the wavelength dependence of laser-induced retinal damage thresholds for q-switched pulses throughout the visible and NIR spectrum. Studies using the a tunable TI:Saph laser and several fixed-wavelength lasers yielded threshold values for 0.1 s exposures from 440 nm to 1060 nm. Laser-induced retinal damage for these exposure durations results from thermal conversion of the incident laser irradiation and an action spectrum for thermal retinal damage was developed based on the wavelength dependent transmission and absorption of ocular tissue and chromatic aberration of the eye optics. Long (1-1000s) duration exposures to visible laser demonstrated the existence of non-thermal laser-induced retinal damage mechanisms having a different action spectrum. This paper will present the available data for the wavelength dependence of laser-induced thermal retinal damage and compare this data to the maximum permissible exposure levels (MPEs) provided by the current guidelines for the safe use of lasers.

In an awake and alert individual, intrinsic eye movements will cause a laser beam spot to move about an extended area of the retina during a long-duration exposure. A single point on the retina will be heated when directly exposed to the laser beam, but will cool when the beam spot is moved to another location. The thermal damage threshold is therefore expected to be larger than the value estimated in standard damage models, in which the eye is treated as a stationary receiver. Experimentally measured eye movement data, recorded during deliberate fixation, were input into a computer program to calculate the increase in temperature occurring in the retina during a long-duration exposure to a continuous wave laser. A simple Arrhenius damage integral model was used to estimate the thermal damage thresholds, which were then compared to the threshold estimated for a stationary eye. The eye movements are found to increase the damage threshold by 18% for 2 second exposures, and 38% for 50 second exposures.

The evaluation of the safety of high-power light sources requires a broad understanding of both thermal and photochemical damage mechanisms in retinal tissue. A comprehensive model which can support complex spectral, temporal and spatial dependency of these effects is essential to evaluation of existing safe exposure limits across a broad parameter space. We present an initial implementation of a thermal damage model along with validating experiments. The model is capable of examining a wide parameter space and is highly extensible to the examination of a variety of damage mechanisms. Also presented is a recent study which examines the effects of a filtered Xenon arc lamp for an exposure duration of ten seconds. This data is examined in relation to the model and a number of historical data points. We also examine exposure limits from the American Council of Government Industrial Hygienists as they apply to these sources.

Corneal epithelial damage thresholds for exposures to sequences of pulses of 1.54 μm infrared radiation produced by an Er fiber laser were investigated. Thresholds were determined for sequences of 8 to 128 pulses at a repetition frequency of 10 Hz and 8 to 256 pulses at 20 Hz. The duration of the individual pulses was 0.025 sec and the 1/e diameter of the laser beam was 0.1 cm. The results show that threshold damage is correlated by an empirical power law of the form H_th = CN^-β, where H_th is the threshold radiant exposure per pulse, and N is the number of pulses. The constant C is different for the 10 Hz and 20 Hz exposures and, for both cases, is greater than the estimated threshold for a single 0.025 sec pulse. Thus the empirical power law breaks down for small numbers of pulses (viz., N< 8), where it overestimates the damage thresholds. Temperature calculations for the threshold exposure conditions show that a critical temperature model also correlates the multiple-pulse injury thresholds.

In order to examine the safety philosophy for laser classes 2 and 2M according to the international laser standard IEC 60825-1, which is based on the existence of aversion responses including the blink reflex, two research projects have been funded by the Federal Institute of Occupational Safety and Health (FIOSH) in Germany. In total, 2,250 volunteers have been investigated in the blink-reflex study in various test situations, where a collimated beam, a divergent beam, a scanned laser line or LED irradiation have been used as a bright optical stimulus. The various test situations included, for example, a free laser beam (like that used in the case of laser adjustment), an eye-tracking system, in which visual tasks have been performed, or LEDs used as single elements or in a cluster. 796 volunteers took part in the aversion response study. Concerning the blink reflex, the mean value of the frequency has been estimated to be 18.36 % within a range extending from 13.8 % up to 36.1 % depending on various parameters and applied optical sources. Their respective influences will be explained. Aversion responses, like head and eye movements, have been found to be relatively seldom events, since only 4.65 % of volunteers showed a reaction which belonged to this category of inherent, physiological, protection reactions. The different parameters which are mainly responsible for the respective results concerning the blink reflex and aversion responses will be dealt with and explained, as they have been experimentally achieved up to now.

Irradiation of the ocular lens of numerous species by near-UV or short-visible wavelengths induces a blue-green fluorescence, which can be a source of intraocular veiling glare. Wavelengths longer than the ~365-nm lens absorption peak induce progressively weaker but also progressively more red-shifted fluorescence emission. The more red-shifted emission has a higher luminous efficiency and, in fact, earlier studies in this laboratory have demonstrated that the lens fluorescence in the non-human primate yields an approximately constant luminous efficiency when excited by equal radiant exposures over the wavelength range from 350 to 430 nm. Now, with the recent development and projected widespread use of "blue" and near-UV diode lasers, a further study extending the measurements of the induced fluorescence efficiency and of the consequent veiling glare to the human lens seemed timely. The current study quantifies the fluorescence intensity induced in the human lens, both in terms of radiance and luminance, as a function of exciting light intensity, excitation wavelength and subject age. The spatial distribution of the emitted fluorescence is also examined. These data are shown to imply that exposure to near-UV/blue wavelength sources at "safe" exposure levels (reference existing laser safety standards) can induce a veiling glare intense enough to degrade visual performance, and that the fluorescence intensity and consequent glare disruption show little dependence on subject age.

In investigations of the eye blink reflex it was found that there exists a dependence on the wavelength of the applied laser device considering the frequency of this physiological reaction. The experimentally acquired correlation shows a much weaker association with the V(λ)-curve than it is normally valid for photobic vision. The experimentally obtained results might be explained by the well-known fundamental WEBER-FECHNER-law of psychophysics and will be given as a blink reflex function in accordance with the STEVENS power law. The results of 788 measurements at 670 nm, 635 nm and 532 nm in lab and field trials in which the head of the tested volunteers was fixed on a chin rest were confirmed in two additionally performed studies with 516 volunteers with an unrestrained head in which either a direct intrabeam viewing or an eye-tracking method was applied in order to simulate typical irradiation situations.

For a given power entering the eye, the level of retinal thermal hazard depends on the retinal image size over which that power is distributed. Maximum permissible exposure limits are given in terms of the angular subtense of the apparent source, which describes the diameter of the retinal image. Based on a simple beam propagation model for a laser beam being transformed by the eye, it will be discussed that both the location as well as the angular subtense of the apparent source depend on the exposure position of the eye in the beam. For a given position, it is important to consider different accommodation conditions of the eye to determine the location and angular subtense of the apparent source. Only when the eye is fixed in the relaxed condition is the angular subtense of the apparent source equivalent with the far field divergence for any exposure position. For a Gaussian beam, when the eye is located in the far field, the beam waist can be considered as the apparent source, while when the eye is located at or close to the beam waist, the apparent source is located in infinity and the angular subtense of the apparent source becomes equivalent with the far field beam divergence.

For a given power entering the eye, the level of retinal thermal hazard depends on the retinal image size over which that power is distributed. Maximum permissible exposure limits are given in terms of the angular subtense of the apparent source α, which describes the diameter of the retinal image. Since this parameter scales the retinal thermal exposure limits (MPE), it is a direct measure of the relative thermal hazard of different retinal images, and thus should be seen as 'thermally effective' rather than 'optical' diameter of the retinal image. From the method given in IEC 60825-1 for the analysis of non-uniform sources, a general method for the analysis of non-top hat profiles was derived and is suggested as general analysis method for the angular subtense of the apparent source for a given image. This and other criteria are compared with the results of thermal models.

The retinal injury threshold for exposure to a laser source varies as a function of the irradiated area on the retina. Currently accepted guidelines for the safe use of lasers provide that the MPE will increase as the diameter of the irradiated area for retinal diameters between 25 mm and 1700 mm, based on the ED50 data available in the late 1970s. Recent studies by Zuclich and Lund produced data showing that the ED50 for ns-duration exposures at 532 nm and ms duration exposures at 590 nm varied as the square of the diameter of the irradiated area on the retina. This paper will discuss efforts to resolve the disagreement between the new data and the earlier data though an analysis of all accessible data relating the retinal injury threshold to the diameter of the incident beam on the retina and through simulations using computer models of laser-induced injury. The results show that the retinal radiant exposure required to produce retinal injury is a function of both exposure duration and retinal irradiance diameter and that the current guidelines for irradiance diameter dependence do not accurately reflect the variation of the threshold data.

The conventional retinal photocoagulation uses continuous wave (CW) lasers which results in pathophysiologic thermal environment to surrounding normal tissues such as neural retina, choroid, and photoreceptors. Selective photodamage of retinal pigment epithelium (RPE), thus sparing photoreceptors can be achieved by using short pulsed lasers. The problem associated with the usage of short pulsed laser is that it is difficult to determine correct dosimetry parameters. The aim of this study is to quantify the influence of different laser parameters over the therapeutic range and to find their optimum values in order to achieve the selective retinal treatment. The present study investigates the laser-tissue interaction by analyzing the transient temperature rise in ocular tissues during repetitive laser photocoagulation. The absorption coefficients based on combined scattering and absorption characteristics for ocular tissues such as vitreous humour, neural retina, RPE, choroid, and sclera are accounted in order to get accurate temperature rise. The laser parameters: wavelength, pulse width, and the laser profile are critical in determining the selective damage. The temperature rise in the neural retina and RPE are quantified by varying the laser parameters. Results reveal that microsecond (μs) pulsed lasers with green wavelength and Gaussian heat source profile is the most effective in selective treatment.

Transpupillary Thermotherapy (TTT) is a retinal laser treatment targeting on occult neovascular membranes. However, the induced temperature increase during irradiation is not exactly known. Model calculations show that differences in pigmentation and vascular perfusion should lead to a different temperature rise under same treatment parameters. In order to evaluate the temperature profiles during TTT, we developed a non-invasive optoacoustic method. The experiments were carried out on enucleated porcine eyes (ex-vivo) and rabbits (in-vivo). Simultaneously to the irradiation with a TTT-laser (λ=810nm, P≤3W) through a slit lamp, pulses from a pulsed dye laser (λ=500nm, τ=3ns, E=5μJ) were applied onto the irradiated area. This probe irradiation induces an ultrasonic pressure wave, its amplitude depends on the temperature of the absorbing media. We measured this pressure wave by an ultrasonic transducer integrated into a contact lens. The induced pressure maximum for porcine RPE samples was found to raise by 14.6% between 37°C and 50°C. Using this relation we determined optoacoustically the temperature increase during TTT. A comparison of the acoustic data with simultaneous temperature measurements by a thermo couple positioned in the choroid showed accordance within ±1.2°C. Differences in pigmentation led to a 1.8 fold induced temperature increase between weak and heavy pigmented eyes. First results in the in-vivo animal study showed an average temperature increase of (2.45 ±0.16)°C for an irradiation of 1W/cm². In conclusion the developed optoacoustic method seems adequate for real-time temperature determination during retinal laser treatments and might serve as a dosimetry control for TTT.

We present the results of a model describing the temperature rise in the cornea during low power diode laser welding of the stroma to induce the repair of corneal wounds. A bi-dimensional model of the anterior segment of the porcine eye was developed. A full thickness corneal cut was considered to be filled by a solution of Indocyanine Green (ICG) in distilled water, which is used to topically enhance the optical absorption of the corneal stroma at the diode laser emission wavelength (810 nm). The typical irradiation conditions used for laser-induced suturing in the transplant of the cornea were considered. The Finite Element Method was used to solve the bio-heat equation inside the cornea wound by using the proper thermal parameters of porcine ocular tissues, providing the thermal response during and shortly after laser treatment. Results indicated a relatively modest temperature increase (of about 20°C), that was spatially confined within the region stained by the chromophore. Calculation of the Arrhenius integral showed no significant thermal damage in the region of the laser-treated wound, thus supporting our previous experimental observations and histological examinations performed on animal models.