Recent studies of retinal damage due to ultrashort laser pulses have shown interesting behavior. Supra-threshold hemorrhagic lesions could not previously be produced with high pulse energy, sub-100 fs pulses, leading to the speculation that nonlinear optical phenomena might mediate these effects. To determine what effect self-focusing will have on laser propagation in the eye, we include this nonlinear phenomena in a calculation of the focal plane position and spot size in the eye as a function of incident power. Light is propagated through the components of the eye using ABCD matrices. The nonlinearity is included using the values for the nonlinear refractive indices for ocular components measured in our laboratory and the diffraction term scaling transformation. We examine how nonlinear propagation changes the irradiance at the retina for nanosecond, picosecond and femtosecond laser pulses with pulse energies near the minimum visible lesion (MVL) threshold for retinal damage. We find that self-focusing can substantially decrease the spot size and increase laser irradiance at the retina. We discuss possible effects this might have on retinal damage.

Threshold measurements for Minimum Visible Lesions (MVL) at the retina are reported for femtosecond (fs) and picosecond (ps) laser pulses in Rhesus monkey eyes using visible wavelengths. The 50% probability for damage (ED₅₀) dosages are calculated for 1 hour and 24 hour post-exposures at the 95% confidence level. The ED₅₀ values are found to decrease with pulsewidth down to 600 fs. At 90 fs the ED₅₀ dosages were noted to increase slightly when compared with the 3 ps and 600 fs values. Fluorescein angiography (FA) was accomplished at both 1 hour and 24 hour post-exposure and did not demonstrate lower threshold for damage, which has been the case for MVL's created with longer pulse durations (>= nanoseconds). At the 90 fs pulse duration, MVLs were not observed below 0.1 (mu) J. At energies greater than 0.1 (mu) J, both MVL and the absence of MVL's were observed up to 1.4 (mu) J. Above 1.4 (mu) J all energies delivered showed MVL development. Out of 138 data points taken at 90 fs, 94 were between 0.1 and 14 (mu) J, and the observed lesions are distributed with approximately 50% probability throughout this energy rate.

Threshold measurements at 90 femtoseconds (fs) and 600 fs have been made for minimum visible lesions (MVLs) using Dutch Belted rabbit and Rhesus monkey eyes. Laser induced breakdown (LIB) thresholds on biological materials including vitreous, normal saline, tap water, and ultrapure water are reported along with irradiance calculations utilizing nonlinear transmission properties including self-focusing. At both pulsewidths the ED₅₀ dose required for the Rhesus monkey eye was less than half the value determined for the Dutch Belted rabbit eye, all thresholds being 1 microjoule ((mu) J) or less. Measurements on the Rhesus eye at 600 fs found the ED₅₀ dose (0.26 (mu) J) to be much lower than the ED₅₀ dose at 90 fs (0.43 (mu) J). But for these two pulsewidths, almost the same energy level was determined for the Dutch Belted rabbit eye (0.94 (mu) J vs. 1.0 (mu) J). LIB threshold measurements at 100 fs and 300 fs using a simulated eye with isolated vitreous found the ED₅₀ dosages to be 3.5 and 6.0 (mu) J respectively. We found in all cases that the ED₅₀ dosages required to produce MVLs in 24 hours for rabbit and monkey eyes were less than the ED₅₀ values measured for LIB in vitreous or saline or any other breakdown values reported. Also observed was the fact that many of the threshold lesions did not appear in the 1-hour postexposure check but clearly showed up at the 24-hour reading which provided for a much lower threshold dose after 24 hours. We discuss the energy levels and peak powers at which nonlinear effects can begin to occur.

We present our clinical evaluation of hemorrhagic and non-hemorrhagic 90 fs single pulses in rabbits and primates. The rabbit and primate eye present unique in vivo models for evaluation of retinal and choroidal laser induced hemorrhages with distinct differences in their retinal anatomy. We found two different hemorrhagic events to occur in the posterior pole with delivery of 90 fs pulses. First, in the Dutch Belted rabbit, we found large amounts of energy per pulse (from 20 to 60 times ED₅₀) were required for formation of subretinal hemorrhages. Second, in the Rhesus monkey, we found significant numbers of small intraretinal hemorrhages from relatively low energy 90 fs pulses. Both the Dutch Belted rabbit and the Rhesus monkey failed to consistently show subretinal hemorrhagic lesions form very high pulse energies. Our findings suggest more energy absorption at the level of the retinal circulation than the choroidal circulation with our pulse parameters. The effects of the laser on the retinal circulation may be due to the use of a wavelength of 580 nm. At this wavelength the oxyhemoglobin to melanin absorption ratio is nearly at its peak (approximately 0.40), perhaps allowing improved absorption in the retinal vasculature. One precaution with this finding, however, are the distinct differences between primate and non-primate ocular systems. Further studies are required to resolve the differences in damage at the level of the RPE and choroid between rabbits and primates.

The physical properties of laser-induced optical breakdown (LIB) in highly transparent, dispersive media, like that found in the eye, are of great interest to the ophthalmic community. We examined the temperature dependent characteristics of LIB thresholds in media with a temperature range of 20 degree(s)C to 80 degree(s)C using nanosecond, picosecond, and femtosecond pulses produced in the visible and near infrared spectral regions. Media used for these studies included high purity water, tap water, physiological (0.9%) saline solution, and bovine vitreous. Ten nanosecond pulses at 532 nm and 60 ps and 90 fs pulses at 580 nm were focused into a sample to produce LIB. Probit analysis was used to determine the 50% probability threshold value (ED₅₀) as the temperature of the media was varied. Additional data was obtained by keeping pulse energy constant and varying temperature. ED₅₀ values for LIB showed no consistent dependence on the temperature of the medium. The theory of the temperature dependence of LIB and the experimental observations for all pulse durations and their implications for retinal damage are discussed.

The purpose of the current study was to identify products of protein degradation and immunohistochemical changes of proteins distribution after high energy laser application. The rabbit lenses were irradiated in vivo with pulse-repetitive (F equals 50 Hz, (tau) _im equals 250 microsecond(s) , P_aver equals 10 W) 1.06 (mu) km wavelength laser radiation. Sodium dodecyl sulfate polyacrilamide electrophoresis of lens proteins following laser treatment showed decrease of 30 and 27 kDa molecular weight polypeptides in soluble fraction, loss of 70 kDa and decrease of 26 kDa molecular weight polypeptides in the insoluble fraction. New high molecular weight proteins in insoluble fraction were observed. Using the anti-MP70 monoclonal antibodies for immunofluorescence microscopy MP70 membrane junctional protein distribution after the laser cataract formation has been studied. Immunofluorescence experiments revealed an abundance of MP70 antigen in the normal lens outer cortex. No labeling after the laser impact in outer cortex and nucleus was found.

The threshold radiant exposure [H_th (J/cm²)] at the retina which produces a minimal visible lesion (MVL) has been investigated as a function of the laser pulse duration (t_p). By considering the optical absorption coefficient of the melanosomal interior, (mu) _a.melanosome, one can calculate the threshold deposited energy, Q_th equals (mu) _a.melanosomeH_th (J/cm³), for the MVL. The t_p-dependence of Q_th is adequately explained for t_p > 16 microsecond(s) by the thermal relaxation of heated melanosomes in the retinal pigmented epithelium (RPE). However, at very short pulses (< 100 ps), there is an apparent on the order of 10-fold drop in the Q_th which is possibly due to the onset of a photomechanical mechanism of damage. Thermoelastic expansion of the laser-heated melanin granules (approximately 10 nm in size) within the 1.5-micrometers melanosome is induced by laser pulses less than 50 ps in duration. This expansion occurs faster than the induced pressure can dissipate from the granules at the speed of sound. The stress relaxation time of a 10-nm melanin granule is about 7 ps. As the accumulated pressure attempts to propagate out of the granule as a pressure wave, the pressure wave suffers reflectance at the granule surface boundary due to the difference in acoustic impedances of the granule and surrounding intramelanosomal matrix. About 12% of the acoustic energy is estimated to be reflected back into the granule as a negative (tensile) pressure wave. This negative stress is hypothesized to elicit cavitation within the melanin granule. This mechanism of intragranule cavitation is a working hypothesis for the mechanism of the MVL in the sub- 50-ps regime. An experimental test of feasibility was conducted using a Q-switched laser and a liver/saline interface. A negative reflectance of about -22% was demonstrated at the liver/saline interface, indicating the ease with which negative stress can be generated at interfaces with mismatched acoustic impedances.

A time-resolved imaging technique to detect shock wave evolution during photofragmentation of hard biological tissues is presented. A theoretical model, previously developed for plasma physics, was successfully applied to fit experimental results providing useful information on the main parameters involved in the acoustic process.

Electromagnetic energy that is carried by light is converted to thermodynamic and mechanical forms of energy, i.e., heat and kinetic energy, when light interacts with tissue. The conversion efficiency from the absorbed radiative energy by an object into the kinetic energy is an important issue in the study of laser-tissue interactions, because the kinetic energy is the source of acoustic signals. Based on the first law of thermodynamics and some simplified assumptions, an expression for the conversion efficiency of optical to kinetic energy has been derived for an isolated, uniformly absorbing sphere. If there is no phase transition, the rule of thumb is that the converted kinetic energy is proportional to the square of the total absorbed radiative energy per unit time, and the square of the linear thermal expansion coefficient; and, it is inversely proportional to the product of the density, radius and the square of the specific heat of the sphere. This result will be used to optimize a design for photo-acoustic measurement of the optical absorption properties of phantoms and biological tissues in vivo.

The ablation dynamics after irradiation of an aqueous dye solution with short laser pulses (pulse duration 5 ns) were observed and compared at different wavelengths by use of time- resolved imaging and stress detection methods. As a tunable source of laser radiation an optical parametric oscillator (OPO) was used. Due to the wide tuning range of the OPO (400 nm to 2500 nm) the following two cases could be investigated: variation of the absorption coefficient by changing the wavelength, and changing the absorbing component of the liquid by changing the wavelength from the visible to the infrared while leaving the absorption coefficient constant. In the latter case similar results were obtained at both wavelengths. A variation of the absorption coefficient yielded different results at each wavelength due to the variation of the maximum temperature and thermoelastic pressure values in the target. Relaxation of the pressure at the free surface of the liquid causes a negative stress which together with the high temperature leads to the rapid growth of bubbles and to material ejection.

The optical properties represented by the absorption coefficient ((mu) _a) and reduced scattering coefficient [(mu) _s(1-g) or (mu) '_s] at (lambda) equals 355 nm of thermally altered albino rat skin were measured in vitro by two methods: (1) a time-resolved stress detection (TRSD) technique which directly measured the effective attenuation coefficient ((mu) _eff) and the absorption coefficient ((mu) _a), and (2) the well-known integrating sphere technique which measured total transmittance (T_t) nd total diffuse reflectance (R_d). The skin pieces were wrapped in water-tight packets and heated for 20 minutes in a calibrated water bath (temperature range: 20 degree(s) - 90 degree(s)C) and the same skin samples were used for both measurement methods. The experimental data were analyzed to specify the absorption and the scattering properties. The results, which were in general agreement for both methods, indicated that denaturation of the rat skin caused a decrease in scattering due to melting of the collagen fibers. The decrease began at 55 degree(s)C and plateaued at 65 degree(s) - 70 degree(s)C and was essentially unchanged at higher temperatures. Absorption was not significantly affected by denaturation except for a transient rise at 50 degree(s) - 60 degree(s)C.

Localizing optical absorption within biologic tissue is compromised by the ubiquitous scattering of light that takes place within such tissues. As an alternative to purely optical detection schemes, regional absorption of optical radiation can be detected and localized within highly scattering tissues by detecting the acoustic waves that are produced whenever differential absorption of radiation takes place within such tissues. When the source of optical radiation is delivered in pulses of <EQ 1 microsecond(s) ec duration, the acoustic waves that are produced lie in the medical ultrasonic frequency range, and can be localized using conventional ultrasonic transducers and reconstruction methodology. Localizing such acoustic waves is not adversely affected by optical scattering. This paper introduces a simplistic theory of acoustic wave production within turbid media. The relationships among the irradiating optical pulse power, regional absorption, and strength of acoustic wave production are developed. Estimates of contrast and spatial resolution are presented, assuming a conventional, focused ultrasound transducer and translational scanning are used. Initial theoretical work indicates that optical absorption can be localized with millimeter spatial resolution for 10% absorption or less in biologic tissues as thick as 6.0 cm using safe levels of optical radiation.

Recent theoretical calculations by our group (2134-14) indicate that regional optical absorption of radiation within highly scattering media, such as biologic tissue, can be localized by detecting photo-acoustic waves that are produced during regional, optical absorption. This paper reports our initial experimental verification that measurable ultrasonic waves are produced when differential optical absorption takes place within turbid media simulating biologic tissue. For these experiments, an aquarium filled with a 0.5% intralipid solution was used to simulate the scattering properties of biologic tissue. Regional, optical absorption was produced by suspending black, latex spheres (3 - 10 mm diameter) within the intralipid bath. A broadband, xenon flash lamp (1 microsecond(s) ec rise time) was used for one set of experiments and a Nd:YAG laser ((lambda) equals 1064 nm, pulse width < 10 ns) was used for another set. A variety of focused, ultrasound transducers (0.5 - 2.5 MHz) were used successfully to detect and localize photo-acoustic waves. Lateral scanning of the transducers was used to localize the position of the absorption cells with a spatial resolution approximately 1 mm.

A new technique based on time-resolved detection of laser-induced stress transients is proposed to visualize the distribution of absorbed laser fluence in turbid and layered biological tissues.

Erbium lasers can effectively cut hard biological tissues despite the limited water content of these materials. However, deposition of thermal energy into the tissue can be a concern for tissue such as teeth. It has been demonstrated in animal models that permanent damage can occur with a pulpal temperature rise of 5 degree(s)C. Therefore, it is necessary to cool such materials during the ablation process to avoid a buildup of thermal energy. an Er:YAG laser was used to ablate hard dental materials, such as dentin and enamel, in vitro. Temperature measurements were made by inserting a thermocouple probe at various locations within teeth. a fine stream of water flowing over the irradiation site was an effective means of cooling the teeth and did not limit the ablation rate significantly over the range of flow rates tested. Temperature rises near the ablation site were limited to less than 5 degree(s)C with the water spray; temperature rises of greater than 20 degree(s)C were seen with no water spray. Moderate variation in the water flow rate had a minimal effect on the temperature rise; most of the thermal energy was convected away with water flow rates as low as 5 ml/min.

A theoretical model is presented to account for the experimental observation that infrared tissue ablation is optimized by the use of wavelengths near the amide II band of proteins. The model recognizes the partitioned absorption of IR photons between protein and water due to overlapping spectral features along with the dynamics of biopolymers, the loss of mechanical integrity in proteins, and the explosive role played by the vaporization of water. The theoretical foundation for this model can be found in previous accounts of thermal confinement, multicomponent models, and selective photothermolysis.

In the regime where the specific time for propagation of stress waves is longer than the laser pulse duration, but shorter than the heat dissipation time, stress can be one of the governing mechanisms of laser-induced ablation of biological tissue. In such inertially confined regimes, knowing the mechanical properties of biological tissue an the kinetics of cracking (in hard tissue represented by bone) and cavitation (in soft tissue represented by meniscus) are important to understand the ablation process. An experimental technique has been developed to study laser-induced stress generation and mechanical properties of tissue in such regimes. This technique is based on monitoring the tissue surface after laser irradiation, using an interferometer that can measure submicron surface displacements on a nanosecond time scale. The subablation threshold laser-induced surface displacements can be related to the stress within the tissue and mechanical properties of the tissue. The surface movement of aqueous solution and meniscus tissue irradiated by 7.5-ns pulses of 355 nm light was consistent with growth and collapse of cavitation bubble. Bone movement was qualitatively consistent with theoretical predictions obtained by solving the equation of motion both analytically and numerically. In the regime where laser beam radius and optical absorption depth are comparable, it is shown that a full 3D analysis is necessary to understand the observed results.

A major consequence of injury to soft tissues is damage to the permeability barriers that protect the chemistry inside cells. This leads to swelling of cells and internal pressurization as structural elements oppose change in volume. For sufficiently large pressurization, mechanical failure of the cell structure may ensue. This failure either results in complete rupture of the cell membrane (lysis) and loss of cytosolic contents or less-catastrophic chemical/mechanical degradation of the cytoarchitecture. Further, since tissues are made-up of adhesively bonded capsules, swelling also acts to disjoin cells in tissues as membrane tensions increase under pressurization. Ultimate failure of a tissue may result from membrane lysis, disruption of intercellular bonding, or rendering of cytoskeletal structure. The course of swelling, pressurization, and rupture following injury depends on tissue `design' as well as the intrinsic strength of cell `materials.'

Picosecond grating spectroscopy is a source of tunable ultrasound in the frequency range from a few MHz to tens of GHz. These ultrasound waves can be used to investigate the mechanical properties of biological materials and tissue. The knowledge of the acoustic properties of tissue in this frequency range is important in order to understand the propagation of shock waves in tissue.

Detailed computational modeling of laser surgery requires treatment of the photoablation of human tissue by high intensity pulses of laser light and the subsequent thermomechanical response of the tissue. Three distinct physical regimes must be considered to accomplish this: (1) the immediate absorption of the laser pulse by the tissue and following tissue ablation, which is dependent upon tissue light absorption characteristics; (2) the near field thermal and mechanical response of the tissue to this laser pulse; and (3) the potential far field (and longer time) mechanical response of witness tissue. Both (2) and (3) are dependent upon accurate constitutive descriptions of the tissue. We briefly review tissue absorption and mechanical behavior, with an emphasis on dynamic loads characteristic of the photoablation process. In this paper our focus centers on the requirements of numerical modeling and the uncertainties of mechanical tissue behavior under photoablation. We also discuss potential contributions that computational simulations can make in the design of surgical protocols which utilize lasers, for example, in assessing the potential for collateral mechanical damage by laser pulses.

The macrophage scavenger receptor is a transmembrane, trimeric glycoprotein which recognizes a number of negatively charged ligands. Cross competition studies of various ligands indicate that the scavenger receptor may bear more than one type of binding site or that there may be more than one type of receptor. In this study we employed resonance energy transfer techniques to identify the location of the binding site for maleylated bovine serum albumin. Using vesicles derived from plasma membrane, we labeled the ligand with a donor probe and labeled the membrane surface with acceptor probes to determine the distance of bound ligand from the membrane surface. Measurements were taken with three different donor-acceptor pairs. Transfer measurements for ligand labeled with dansyl and HAE (hexadecanoylaminoeosin) as the acceptor yielded a distance of 47 angstrom from the surface of the plasma membrane. Similar measurements employing the same donors but using ORB (octadecylrhodamine B) as the acceptor produced a distance of 58 angstrom. Assuming that the receptor extends perpendicularly from the cell surface this distance lies within the two receptor `domains' closest to the cell surface. These domains include the spacer region, with no distinct proposed structure and a region which has sequence similarity to an alpha helical coiled coil. No transfer was observed between ligand monolabeled with fluorescein and DiI in the membrane. This suggests that the orientation of mal-BSA bound to receptor places the fluorescein probe too far from acceptor on the membrane surface to experience energy transfer.

Benzoporphyrin derivative, monoacid ring A (BPD-MA) is a second generation porphyrin photosensitizer, with a significant absorption at 692 nm. The ability of two different lasers (a high-intensity pulsed ruby laser, and a continuous wave (cw) argon-ion laser pumped dye laser) in producing photodynamic damage to human bladder carcinoma cells in vitro under similar conditions was compared. Cells incubated in 0.14 (mu) M BPD-MA for 3 hours were irradiated with 1 or 3 J/cm² with either pulsed or cw irradiation at 694 nm. Cell survival was determined using an MTT assay. With the ruby laser essentially no phototoxicity was observed at the high intensity pulsed irradiances used, whereas 38% and 6% survival rates were observed for 1 and 3 J/cm², respectively, using cw irradiation. Possible explanations for the lack of BPD-MA phototoxicity using the ruby laser are: rapid photodegradation, saturation and excitation into higher excited states of the sensitizer. No BPD-MA photodegradation was observed in 1.4 (mu) M BPD-MA in 10% fetal calf serum solutions using the ruby laser. However, an oxygen-dependent photodegradation with the formation of a chlorin-type photoproduct was observed in these solutions using cw irradiation. A simple calculation indicated that the high pulse irradiances used in this study (4.4 X 10⁷ W/cm²) were approximately 3 orders of magnitude greater than required for the onset of saturation. If higher excited states (S_n or T_n) are populated, they do not undergo any photochemistry resulting in phototoxicity or in photoproduct formation. These results show that with the low saturation threshold of BPD-MA, the choice of source and irradiance are important considerations in planning a therapeutic regime.

Intracellular modifications of sensitizers during PDT were observed with combined measurements of cw and time-gated microscopy and spectroscopy. Protoporphyrin when stimulated with 5-aminolevulinic acid (ALA) showed photobleaching after irradiation with blue light (1 - 10 J/cm²) in competition with the formation of photoproducts (i.e., photoprotoporphyrins). The anionic meso-tetra(4-sulfonatophenyl)porphyrin (TPPS₄) was incubated in cells seeded at low cell density (isolated cells; 25 cells/mm²) or high cell density (confluent growing cells; 500 cells/mm²), respectively. A similar granular fluorescence pattern, cw and time-gated fluorescence spectra could be observed before light exposure in both cases. With increasing irradiation a redistribution from the cytoplasm to the nucleus in addition with a pronounced formation of a fluorescent band around 615 nm was dependent on the growth phase of the cells and could be detected mainly for isolated cells. This species was correlated with a short fluorescence decay time and detected with an `early' time gate between 0 - 5 ns, whereas the neutral TPPS<sub>4</sub> molecule was detected within a `late' time-gate between 10 - 15 ns.

Optical spectroscopy techniques are frequently used for non-invasive detection of abnormal tissues. For these techniques it is necessary to know the tissue optical properties, such as absorption and scattering coefficients, anisotropy factor and intrinsic fluorescence yield. Using a collimated white light illumination system, polarized on-axis light detection and integrating sphere techniques, optical properties of normal and cancerous bronchial tissue were measured for the wavelength range of 400 to 700 nm. Fluorescence microscopy was used to measure the fluorescence excitation function and spectra of bronchial tissue as a function of depth into the tissue. The distribution of 442 nm He-Cd laser light inside the tissue was calculated by Monte Carlo simulation. The propagation of excited green, yellow and red fluorescence inside the bronchial tissue was simulated using the Monte Carlo model and fluorescence escape functions were calculated for various depths. By comparing the total fluorescence of normal and carcinoma tissue calculated from the Monte Carlo simulation with in vivo fluorescence measurement results, the fluorescence characteristics of normal and abnormal bronchial tissue could be explained.

Time-resolved light transport in composite tissues is simulated using the Monte Carlo technique. Snapshots of spatial distributions of physical quantities, including light absorption rate, light fluence rate, and diffuse reflectance rate, are presented. Such multiple snapshots with a given time interval can be shown sequentially to achieve an animation effect. This animated simulation is a tool that aids in the general understanding of light transport in tissues. For example, the simulation of time-resolved spatial distribution of light fluence rate inside a tissue illustrates how fast light is dispersed inside tissues. The simulation of diffuse reflectance rate as a function of time of a short-pulsed laser incident upon a piece of tissue containing a buried object shows that early reflected light does not carry imaging information of the object. The imaging quality of the object can thus be improved by rejecting the early-arriving reflected light.

The aim of this study was to calculate the light fluence for various PDT applications with a Monte Carlo method. Different applicator geometries and the related illuminations are computed in a 3D-multilayer tissue model. The applicators we calculated include various surface geometries, intensity and angular profiles as well as tissue parameter variations, and different wavelengths. The resulting fluence contours in conjunction with a certain dye concentration allow a prediction of the expected damage zone after PDT in the tumor tissue. To measure tissue parameters ex vivo we built up a spectrometer consisting of two integrating spheres. The light source we use is a cw Ti:sapphire laser tunable from about 670 nm to 760 nm without change of optics. We use a combination of direct and indirect measurements. By estimating the specular reflection and direct transmission from a tissue sample (approximately 490 micrometers ) we get the refractive index n and the extinction coefficient (mu) _(tau ). We also measure the diffuse reflection as well as the diffuse transmission with the integrating spheres. To calculate the missing parameters (mu) _a and g we use an inverse Monte Carlo simulation (MCS) with the Henyey-Greenstein phase function. Simulation of the tissue sample including the boundary and geometry effects leads to absorption coefficients that are up to a factor of 3 lower in comparison to good analytical models. The loss of diffuse light can be taken into consideration.

Decreased corneal collagen birefringence in transmission polarizing microscopy is an observable quantitative measure of degree of tissue damage. a damage assessment algorithm based on monochrome tissue images exhibiting decreased birefringence is presented, identifying image regions with designated damage values. Initially, several video frames of the microscopic tissue image are time-averaged to reduce additive noise components, and an additional multiplicative correction for optical nonuniformities is performed. Subsequently, linear scaling improves the low contrast of the birefringence image by increasing the image value set to the standard 8-bit range of integers in the interval. Finally, morphological erosion employing a 5 X 5 pixel template reduces impulsive bright tissue artifacts. Formal damage quantification consists of a 25 X 25 pixel template mean filtering of the image, followed by background subtraction and scaling. This produces the components required for the damage computation according to the volume fraction kinetic damage model. In this investigation, the corneal damage region resembles and edge. Therefore, standard edge detection algorithms applied to the eroded image are compared the damage region identified by this algorithm. This damage quantification algorithm provides significantly superior edge delineation relative to Roberts, Sobel, Frei-Chen, Laplacian of Gaussian, and Blur-Minimum and Erosion Residue morphological edge detection algorithms.

The objective of this in-vivo study was to assess the possible use of temperature sensitive liposomes in an established model such as liver as a new approach to monitor the temperature induced by a laser. Temperature sensitive liposomes (DSPC: distearoylphosphatidylcholine) loaded with carboxyfluorescein were prepared by the Bancham procedure. These liposomes (1 ml solution) were injected into adult male wistar rats. Two hours later, the liver was exposed and irradiated with a 100 W Nd:YAG laser using pulses lasting from 100 ms to 260 ms. Simultaneously, the surface temperature was recorded with a thermographic camera. The fluorescence emission was measured with a fluorescent imaging system. The results show that the dye is released in response to laser energy. The amount of the drug release increases linearly with increasing temperature in the range 45 degree(s)C - 60 degree(s)C. Moreover, the release occurs in a short period of time upon brief exposure to its phase transition temperature. The temperature range could be modified and adapted by using different liposomes formulation, for example DPPC (dipalmitoylphosphatidylcholine) for lower temperature (35 - 45 degree(s)C) or DSPE (distearoylphosphatidylethanolamine) for higher temperature (65 - 75 degree(s)C).

Residual thermal damage produced by a scanned quasi cw CO₂ laser was measured in pig skin. The effects of scan speed on thermal damage distribution for laser dwell times ranging between 1 and 150 msec were examined. Significantly larger thermal damage zones were produced along the crater wall for laser dwell times longer than 50 msec. Thermal damage along the crater base was constant independent of dwell time. The preliminary experimental results suggest that quasi cw CO₂ can consistently produce less than 200 micrometers zones of thermal damage if laser parameters are carefully chosen.

We have studied dynamic changes in optical properties of various tissues during argon and pulse Nd:YAG laser irradiation while monitoring tissue surface temperature. High power laser radiation induces reversible and/or irreversible changes in the optical behavior of the tissue. Reversible changes in diffuse reflectance and total transmittance can be as much as 15% and 20% of initial values, respectively. We are currently investigating the mechanism responsible for the observed reversible changes.

Linear birefringence (LB) is a polarization-specific property of many semi-crystalline structures in tissue. Specifically, collagen, with its triple helix conformation, exhibits LB in its native state. Rat tail tendon (RTT) was chosen for the LB experiments because it is > 90% collagen and the collagen fiber alignment is nearly parallel with the RTT length. This alignment results in RTT exhibiting uniaxial characteristics such that two properly chosen optical axes display differing refractive indices ((Delta) n equals n_slow - n_fast). RTT, which has an elliptical cross section, has its slow axis parallel to the tendon's length and a fast axes along the tendon's cross section. Native RTT has a refractive index difference of (Delta) n equals 1.5 X 10^-3. For a typical tendon thickness of 200 micrometers , the phase shift, (delta) equals n*d (d, diameter), is approximately equal to 300 nm (transmission measurement). Heating of RTT results in a repeatable loss of (delta) . If monochromatic light is used the sample's output intensity is proportional to sin²((delta) (pi) /(lambda) ) where (lambda) is the wavelength of the light. Thus, given the native phase shift, the incident light's wavelength may be chosen such that the sample's loss of LB with heating is intensity- mapped on the sample's image.

Human enamel and dentin were cut using a 2.8 micrometers erbium laser beam in conjunction with water spray. Ablation rates of the order of 0.14 mm³/s were achieved for both tissues at 4 W average power. An ablation threshold of 0.28 W was determined for dentin when using the water spray. When above threshold, the volume of tissue ablated per joule was discovered to be nearly constant, not related to the average laser power. Comparative microscopy between tissue irradiated with and without water spray demonstrated a lack of thermal effects when the water spray was utilized.

We experimentally and theoretically studied interpretation of the waveform signal which was obtained by the fiber-optic probe method during Ho:YAG laser ablation. We monitored behavior of the ablation bubble which occurs at the fiber tip during the ablation by means of developed fiber-optic probe method as well as time-resolved photography to investigate the information which involves the waveform signal. We used water and agar as model materials for different purposes. We determined that the waveform signal from the fiber-optic probe method is mainly attributed to the reflection of the boundary between the water-vapor bubble and surrounding material/tissue. We also found that the intensive shockwave which is induced may be monitored by our method.

Recent studies have established clinical application of laser ablation of cartilaginous tissue. The goal of this study was to investigate removal of cartilaginous tissue using diode laser. To enhance the interaction of laser light with tissue, improve the ablation efficiency and localize the extent of laser-induced thermal damage in surrounding tissue, we studied the use of a novel delivery system developed by MicroFab Technologies to dispense a known amount of Indocyanine Green (ICG) with a high spatial resolution to alter the optical properties of the tissue in a controlled fashion. Canine intervertebral disks were harvested and used within eight hours after collection. One hundred forty nL of ICG was topically applied to both annulus and nucleus at the desired location with the MicroJet prior to each irradiation. Fiber catheters (600 micrometers ) were used and positioned to irradiate the tissue with a 0.8 mm spot size. Laser powers of 3 - 10 W (Diomed, 810 nm) were used to irradiate the tissue with ten pulses (200 - 500 msec). Discs not stained with ICG were irradiated as control samples. Efficient tissue ablation (80 - 300 micrometers /pulse) was observed using ICG to enhance light absorption and confine thermal damage while there was no observable ablation in control studied. The extent of tissue damage observed microscopically was limited to 50 - 100 micrometers . The diode laser/Microjet combination showed promise for applications involving removal of cartilaginous tissue. This procedure can be performed using a low power compact diode laser, is efficient, and potentially more economical compared to procedures using conventional lasers.

For the XeCl-excimer (308 nm, 115 ns) laser the contribution of photo-thermal and photo- mechanical processes was studied during the penetration of aortic tissue by bare fibers in dependence of fiber diameter, exerted force, pulse repetition rate, and fluence. Though, theoretically, Monte-Carlo simulation shows that the light penetration depth is diameter dependent for fibers up to 550 micrometers , experimentally, tissue penetration was not affected when the fiber diameter increased from 300 to 950 micrometers . Also the change in optical properties of tissue due to denaturation did not affect the penetration behavior significantly. Fiber tissue penetration increased when the exerted force increased, but it started only after a series of 5 - 20 initial pulses. The penetration per pulse became only slightly larger increasing the pulse repetition rate from 2 to 60 Hz while the tissue temperature rise near the fiber was up to 60 degrees. Increasing the temperature of the surrounding tissue itself prior to laser exposure only slightly affected tissue penetration in the case of both normal and denatured tissue. Delivery of laser energy in successive pulse trains, accelerated penetration after the first train. Close-up, high speed video recording showed the presence of rapidly expanding, short-life (50 - 150 microsecond(s) ) vapor bubbles, in the first instance on top of the tissue surface and later in the tissue itself while the fiber was penetrating the tissue. From our measurements and observations it is inferred that the mechanical effect of the bubble is especially important for the penetration of the fiber into the tissue. Theory suggests that the energy is deposited in a 100 - 200 micrometers layer in front of the fiber where the temperature is instantly increased to above boiling temperature inducing a rapid expanding vapor bubble. The mechanical force of the bubble breaks down tissue structures to small pieces creating a channel for the fiber to penetrate the tissue. So the formation of water vapor seems to be the dominant mechanism for tissue ablation.

Surface epithelial damage by Ho:YAG laser and recovery were studied using histology and electron microscopy. Rabbit skin was irradiated with fluence varying from 55 J/cm² to 680 J/cm². Laser damage was determined by histological measurement of three major injury indicators: surface lesion width, depth of photocoagulation, and depth of thermal damage. When the fluence increased, the surface lesion widened and the photocoagulation zone extended deeper into the dermis. The thermally damaged zone (60 degree(s)C < T < 100 degree(s)C) remained at a relatively unchanged depth (about 1 mm) throughout our fluence range. The muscle and nerve tissues appeared to remain intact under most of our irradiance except at 500 J/cm² and greater. Thermally injured tissues began recovery within a short period and eventually returned to normal; electron microscopic findings indicated that severe swelling occurred in the individual collagen fibrils, but they were not disrupted and usually recovered to appear normal. A layer of new epithelium started growing underneath the photocoagulated zone around day 3. After 7 days, most photocoagulated tissue was partially, in some cases completely, separated from the skin by the new epithelium. The damage and recovery parameters established should aid in the clinical use of Holmium laser in treating lesions, benign or malignant, in hollow tubular organs and on surface epithelia.

This article presents a modified method of measuring the optical-transport-coefficients of intralipid: the diffuse reflectance of intralipid with added-ink R_d^ink is measured by using an integrating sphere to calculate the scattering coefficient (mu) '_s, the effective attenuation coefficient (mu) _eff is measured by scanning the surface of pure intralipid suspension with a cut-end, high NA fiber-optic tip ((phi) 600micrometers , NA equals 0.48) in order to directly derive the absorption (mu) _a of pure intralipid. In the same way, their wavelength dependencies between 0.48 - 0.85 micrometers are measured by utilizing Ar⁺, dye and Ti:Sapphire lasers. Experiments show that (mu) _s((lambda) ) varies with (lambda) according to the previously reported Mie theory, (mu) '_s((lambda) ) decreases with (lambda) while R_d^ink((lambda) ) is nearly invariant within the wavelength range; the scattering anisotropy g((lambda) ) tends to decrease linearly with (lambda) from 0.91 to 0.78; (mu) _a((lambda) ) first decreases with (lambda) till (lambda) approximately equals 0.61 micrometers and then gradually increases with (lambda) . In the R_d^ink experiments, it has been found that when the port of the integrating sphere is lifted above the liquid surface, the dependence of the measured intensity with the height H can be well-fitted into an exponential relation for H <EQ 3 cm and Lorentzian relation for H <EQ 10 cm, so R_d^ink can be accurately derived by a simple extrapolation over a few measured points to H equals 0. Monte-Carlo simulation is applied to analyze the results.

A finite-difference model provides computer simulations of laser ablation, depicting a dynamic process of surface dessication, temperature rise, carbonization, and explosive subsurface vaporization, which repeats cyclically. The model considers the role of changing tissue optical properties, thermal diffusion, surface water evaporation, water diffusion, tissue dessication, transient carbonization, subsurface explosive vaporization. The parameters of the model were adjusted to yield an ablation velocity, v_abl (mm/s), which matched a typical experimental value from the literature. Then the effect of each parameter on v_abl was examined by plotting v_abl versus variation in that one parameter while holding all other parameters constant. The major factors influencing v_abl appear to be the threshold for explosive vaporization [Q_the(J/cm³)] and the rate of carbonization expressed in terms of its optical absorption [(delta) (mu) _a.carb/(delta) t(cm^-1 s^-1)]. The ablation process is dynamic not constant, but the average ablation velocity can be adequately modeled as the simple boiling of water caused by heat deposition in a 2-5-micrometers time-averaged thickness of carbonized tissue.

Issues of coagulation control were considered by simulating a controlled surface temperature irradiation using thermal feedback to execute an appropriate temporal profile for laser power. In order to maintain a relatively `constant' temperature at the surface of the tissue, a non- uniform pulse sequence would be required. `Constant' surface temperature irradiation avoids high temperature effects, achieves relatively slow, steady progression of damage, allowing potential real-time monitoring and control of coagulation front position. Furthermore, the difference in damage depth prediction using a constant property model as compared with a temperature dependent optical property model is much less for a `constant' surface temperature irradiation than for a free running laser irradiation.

The intense interest in the investigation of erbium laser radiation in medicine is due to the fact that radiation at 3 micrometers is very strongly absorbed by water, which is present in all biological tissue. As a consequence of this high absorption the interaction of pulsed radiation is characterized by an explosive process with a low ablation threshold and a thin coagulation zone along the laser incisions. Erbium lasers, therefore, have a wide field of potential medical applications which become even more attractive with the availability of reliable delivery systems. An interesting situation arises in orthopaedics and angioplasty, where a precise cutting instrument is needed in a liquid environment. For this reason, we experimentally investigated the interaction mechanism of fiber transmitted, pulsed, free-running and Q- switched Erbium:YSGG ((lambda) equals 2.79 micrometers ) and Erbium:YAG ((lambda) equals 2.94 micrometers ) laser radiation with liquid water. The dynamics of the bubble formation and the propagation of shockwaves in water was studied and visualized by flash photography. Acoustic transients of a few hundreds of bars accompanying the ablation process were measured with a needle hydrophone. A clear correlation between the spikes of the laser pulse and those of the pressure signal was observed. Additionally, strong pressure transients were measured after the end of the laser pulse, which could be associated with the collapse of the vapor bubble and further collapses after multiple rebounds. The influence of pulse energy, fiber size and pulse duration on the formation and the amplitude of the pressure waves is demonstrated.

A cw 1.48 micrometers diode-laser microsurgical procedure is investigated allowing drilling of mouse zona pellucida without micromanipulators or handling of the egg outside the culture dish. The laser beam (60 - 70 mW at the focal point) and a coaxial red light aiming laser are directed through the objective (45 X) of an inverted microscope and focused in spots of 2 - 3 micrometers diameter. Mice zygotes are suspended in groups of 15 - 20 (Nunc culture dishes) in 1 ml culture medium. Egg zona is positioned with the microscope stage on the control spot and exposed to laser light (10 - 20 ms; 0.65 - 1.3 mJ). One laser pulse is sufficient to drill openings ranging from 5 - 7 micrometers diameter depending on laser power and exposure time. Drilled zygotes (N equals 150) develop to the blastocysts stage at a rate (70%) comparable to the control. There is no evidence of thermal damage under optical microscopic observation. In conclusion, the 1.48 micrometers laser radiation allows us to drill holes in mouse zona pellucida in a rapid, simple and non touch procedure. Its high absorption by water and non-mutagenicity makes it a useful tool for assisted fertilization procedures.

In this study the role of acoustical transients during pulsed holmium laser ablation is addressed. For this the collapse of cavitation bubbles generated by 2.12 micrometers Cr:Tm:Ho:YAG laser pulses delivered via a fiber in water is investigated. Multiple consecutive collapses of a single bubble generating acoustic transients are documented. Pulse durations are varied from 130 - 230 microsecond(s) and pulse energies from 20 - 800 mJ. Fiber diameters of 400 and 600 micrometers are used. The bubble collapse behavior is observed by time resolved fast flash photography with 1 microsecond(s) strobe lamp or 5 ns 1064 nm Nd:YAG laser illumination. A PVDF needle probe transducer is used to observe acoustic transients and measure their pressure amplitudes. Under certain conditions, at the end of the collapse phase the bubbles emit spherical acoustic transients of up to several hundred bars amplitude. After the first collapse up to two rebounds leading to further acoustic transient emissions are observed. Bubbles generated near a solid surface under water are attracted towards the surface during their development. The final phase of the collapse generating the acoustic transients takes place directly on the surface, exposing it to maximum pressure amplitudes. Our results indicate a possible mechanism of unwanted tissue damage during holmium laser application in a liquid environment as in arthroscopy or angioplasty that may set limits to the choice of laser pulse duration and energies.

Irradiation with pulsed lasers can change mechanisms and efficacy of photodynamic therapy (PDT) depending on the laser pulse parameters. Since most photosensitizers have a relatively high triplet quantum yield and triplet lifetimes of tens of microseconds, even moderate power densities below 100 kW/cm² can lead to a saturation of the singlet oxygen production, thereby reducing the PDT effect. A simple quantitative model is developed to estimate this effect. According to this, for laser pulses not longer than the triplet lifetime, the PDT efficacy depends on the product of single pulse energy, irradiation wavelength, and the extinction coefficient of the photosensitizer. Peak irradiance and pulse width have minor influence on the efficacy of pulsed irradiation, which decreases as the triplet quantum yield reaches one. The model is supported by in vitro experiments with Photosan 3 and in vivo and in vitro experiments with Photosan 3, Photofrin, aluminum sulphonated phthalocyanine (AlSPc) and benzoporphyrin derivative monoacid ring A (BPD-MA) reported in the literature.

In this work we present the experimental results of a comparative study between polarized and nonpolarized laser light on the healing behavior of lesions created by the application of liquid nitrogen over the skin of Lewis rats. The aim of our work is understanding in the interactions of laser light and biological matter. In previous work we succeeded in showing that coherent light plays an important role in wound healing but the effect of polarization was not considered. We improved our experimental set up by simply adding a polarization filter and adjusting the power and exposure time to obtain an energy density of about 1.0 Joules/cm² in order to be able to compare it with the results of our previously mentioned work. Our actual results demonstrated that polarized and nonpolarized laser light play different roles in the healing process.

The transformation of light energy into thermal energy with extremely high temperatures, the evaporation of interstitial and intracellular fluids, and the cytoplasmic proteins coagulation are the most important factors in the mechanism of high-power lasers effect on biological tissues. A set of dystrophic disorders develops in tissues as a result, up to the coagulative necrosis, which lays in the basis of the laser thermal crust at incised edges. With CO₂ laser the damage is evident from the first cell layers. Its size is in the linear correlation with exposure time. The Nd:YAG and argon lasers' light penetrates the superficial cell layers without damage practically and realizes in deeper well vascularized tissue layers, the submucous layer of the gastrointestinal hollow organs, in particular. It depends on the closeness of the irradiation spectrum of absorption of hemoglobin and result in blood coagulation in the vascular lumine with formation of the `coagulative laser thrombi.' That explains a wide use of laser irradiation in urgent endoscopy for arresting acute gastrointestinal hemorrhages. For these reasons Nd:YAG laser `contact scalpel' technique with sapphire tips is used for incisions on parenchymatous organs with simultaneous blood coagulation in vessels lumina with good hemostasis and holestasis (hepatobiliar surgery), and for pancreas and thyroid surgery, in gynecology and other surgical areas.

Low energy laser irradiation in clinical practice can be divided into two categories: irradiation of located parts of the body and laser acupuncture therapy. If the laser with fixed wavelength and proper power is input into certain particular points of the body, it may produce good systemic physiologic effects. This has been proved by many tests on animals and in clinical practice. Some clinical applications are discussed as representative of the therapy. According to the TCM theory on `Ching-lo' (channels), we used the 2 mW - 5 mW laser to treat experimentally more than 30 patients for leuckocytopenia, decreasing of platelets and a lot of inflammatory masses. The effects are dramatic. About the mechanism, we realize that first, the human body is irradiated by the laser, the photon is absorbed by cells, and the cells are polarized and activated. In the next step, the activated energy is transported along the resonance dipoles of the human body. Various physiological functions of the organism and the clinical effects are shown as the final results.

The eye is exposed daily to UVR from skylight and ground reflections when outdoors in sunlight. Additional exposure occurs daily from artificial sources such as fluorescent lamps. Some workers, notably welders, are exposed to industrial sources of UVR. The geometry of exposure critically influences the actual UVR dose to the cornea and lens. When exposed to bright light, squinting reduces UVR exposure. the optical properties of the eye and behavioral responses to bright light both contribute to limiting actual UVR exposure. The actual daily dos of UVR is considerably less than what many previous investigators have assumed. The geometrical, as well as temporal and spectral, aspects of ocular dosimetry will be reviewed in order to allow participants a better insight into the practical impact of many laboratory studies of UVR effects upon ocular tissues.

the major human health effects of solar and artificial UV light occur from the UVB and UVC wavelength ranges and involve a variety of short-term and long-term deleterious changes to the skin and eyes. the more important initial damage to cellular macromolecules involves dimerization of adjacent pyrimidines in DNA to produce cyclobutane pyrimidine dimes, (6-4) pyrimidine- pyrimidone, and (6-4) dewar photoproducts. these photoproducts can be repaired by a genetically regulated enzyme system (nucleotide excision repair) which removes oligonucleotides 29-30 nucleotides long that contain the photoproducts, and synthesizes replacement patches. At least a dozen gene products are involved in the process of recognizing photoproducts in DNA, altering local DNA helicity and cleaving the polynucleotide chain at defined positions either side of a photoproduct. Hereditary mutations in many of these genes are recognized in the human genetic disorders xeroderma pigmentosum (XP), Cockayne syndrome (CS), and trichothiodystrophy (TTD). Several of the gene products have other functions involving the regulation of gene transcription which accounts for the complex clinical presentation of repair deficient diseases that involve sensitivity of the skin and eyes to UV light, increased solar carcinogenesis (in XP), demyelination, and ganglial calcification (in CS), hair abnormalities (in TTD), and developmental and neurological abnormalities

Retrospective epidemiological studies implicate solar ultraviolet as a contributing factor in several human corneal/conjunctival disorders including spheroidal degeneration, pterygium and pinguecula. The inferior bulbar(ocular) conjunctivae of 64 human volunteers were irradiated with narrow band ultraviolet radiation biomicroscopy, differential in vivo staining, and impression cytology. The conjunctival response was symptomless and characterized by injection, chemosis, damaged epithelial cells, and the presence of inflammatory cells. The action spectrum showed a similar response to that for human corneal epithelium but with slightly lower damage thresholds (3mJcm^-2at 270 nm). No response was produced at 330 nm. Irradiance levels were the same order of magnitude as solar UVB and these results suggest the sub-clinical damage would be produced within minutes of direct exposure to sunlight. The potential for repeated conjunctival trauma supports the hypothesis that chronic exposure to enviornmental UVR contributes to degenerative changes in the cornea and conjunctiva.

A coincidence of the locations of foci of scattered light in the anterior eye with the usual locations of common sun-related eye conditions has been observed. These phenomena may explain the pathogenesis of pterygium and the initial location of certain cortical lens opacities and eyelid malignancies. Human and bovine eyes were used to demonstrate that the anterior eye acts as a side-on lens system. Light incident at the temporal limbus can be concentrated at the nasal limbus or beyond or at the nasal crystalline lens equator. The main pathways of light are transcameral and this is demonstrated by the use of baffles. Although this phenomenon is obvious with visible light, focusing of light at 308nm can be demonstrated. Computer-assisted optical ray tracing in a standard human anterior segment model showed that the peak intensity at the distal limbus is approximately twenty times that of the incident light intensity. The degree of limbal focusing is determined by corneal shape and anterior chamber depth. Such light focusing may be particularly injurious to corneal and lenticular epithelial stem cells. These observations provide circumstantial evidence that peripheral refraction phenomena are involved in the pathogenesis of the anterior ophthalmohelioses. Adequate lateral protection of the eye from increasing ultraviolet insolation may be prudent.

Light incident at the temporal limbus of the peripheral anterior eye is focused onto the nasal limbus, the usual site of pterygium formation. Parameters which may contribute to observed individual variations in the degree of limbal light focusing were assessed. Computer assisted ray tracing techniques were applied to a human anterior segment model. We varied the angle of incident light ((Theta) , 5 to 18 degree(s) posterior to coronal plane), corneal radius of curvature (r_(omicron ), 7.2 to 8.4 mm), and shape factor (p, 0.50 to 1.0) and calculated the effect in distal limbal intensity. The clinical observation of individual variations in the degree of limbal light focusing may be due to differences in corneal topography. Further study is required to determine whether individuals with corneas capable of developing intense limbal foci may be predisposed to developing pterygium.

Both solar and laser sources may induce punctate foveal retinal damage. Unprotected viewing of the sun or bright blue sky represent potential solar radiation causes of photic maculopathy that may induce punctate foveal damage. Laser induced macular retinal damage is another more recent kind of photic maculopathy. Most documented cases of laser photic maculopathy have involved acute laser exposure generally from Q-switched visible or nonvisible near IR laser systems. In our comparison of these types of photic maculopathies, we have employed conventional as well as spectral and confocal scanning laser ophthalomoscopy to evaluate the depth of the photic maculopathy. Functionally, we have observed a tritan color vision loss present in nearly all photic maculopathies.

The measurements of ozone content, evaluation of UV radiation and their links with skin cancer in Hungary have been studied for the last three decades. The total ozone content of an air column above Hungary has been measured by the Hungarian Meteorological Service since 1969 using Dobson-spectrophotometer. The measurements of UV-B radiation started in 1993 by three Robertson-Berger equipments and LI-1800 spectroradiometer. It was found a decreasing trend of ozone content 1.7% per 10 years. Since 1991/92 winter the ozone conditions of the stratosphere have been perturbed. Such low ozone values that have been observed in two winters successively never occurred. Deficits in monthly averages: 1991 Dec: -6%, 1992 Jan; -17%, Feb; -9%, Dec; - 10%, 1993 Jan; -16%, Feb; -17%. Statistical analysis of the patient material of the Eastern region of Hungary, characterized by a rather high intensity of sunlight and UV rays, has shown a significant increase in light induced skin disorders in recent decades. Ninety-six photoallergic and phototoxic cases followed up in 1966 rose to 336 (1977) and 788 (1993) whereas the numbers of patients with basal cell carcinoma and malignant melanoma increased two- and fivefold, respectively, from 1966 to 1993. A UV personal dosimeter has been developed to measure exposure of the skin to UV-B radiation. These SUNTEST UV-sensitive strips for general public are produced by FORTE Photochemical Company.

The effect of the UV-A and blue light on the accumulation of lipid peroxidation products and activities of succinate dehydrogenase and superoxide dismutase in the retina was examined in eye cup model of dark and light adapted frogs R. temporaria. Retinas were exposed to UV-A radiation (8 mW/cm²) and blue light (10 to 150 mW/cm²) for periods from 5 min to 1 hr. We have measured TBA-active products both in the retina homogenates and in the reaction media. Enzyme activities was measured in the retina homogenates only. The measurements revealed a significant increase in the endogenous and exogenous forms of lipid peroxidation products in the retina of dark adapted frog (1.6+/- 0.4; 1.4+/- 0.3 nmole TBA-active products per mg protein, respectively) compared to light adapted (0.85+/- 0.16; 0.32+/- 0.06 nmole TBA-active products per mg protein, respectively). In the same conditions succinate dehydrogenase activity was decline more than 50% but superoxide dismutase activity didn't decrease. Disorganized inner and outer segments were observed after 40 min exposures. No light microscopic changes were detected after 5 min exposures. Light damage was significantly higher in the retina of dark adapted frog. The results indicate that the retina from eye cup of dark adapted frog is more susceptible to UV-A and blue light damages.

Human exposure to solar UVR can be assessed by using multi-site passive dosimeters such as the polycarbonate CR-39. The variation in dosimeter response (absorbance) for ten sets of ten simultaneously exposed, then processed, badges was less than 6%. Possible sources of this variation include inaccuracies inherent in the dosimeter badge fabrication and calibration, and variation in experimental conditions during badge exposure and processing. Inherent inaccuracies may be minimized through use of homogeneous material, suitable backing substrate and by developing fabrication and cleaning techniques for the badge. Calibration of dosimeters may require use of both solar and lamp sources, with errors caused by seasonal changes in spectral content and proportion of direct to diffuse light. Regular spectroradiometric calibration of dosimeters is necessary to reduce errors of up to 50% which are introduced by seasonal effects. Experimental conditions during exposure depend on the activity of the wearer on the site of badge attachment and on its attitude to direct sunlight. Etchant concentration increased approximately 1% for each 100 badges processed. Other etching parameters such as etch time and temperature were varied +/- 10% from the standard values, and produced changes of 36% and 77% respectively.

Current safety limits for cataract development after acute exposure to ultraviolet radiation (UVR) are based on experiments analyzing experimental data with a quantal, effect-no effect, dose-response model. The present study showed that intensity of forward light scattering is better described with a continuous dose-response model. It was found that 3, 30 and 300 kJ/m²UVR_300nm induces increased light scattering within 6 h. For all three doses the intensity of forward light scattering was constant after 6 h. The intensity of forward light scattering was proportional to the log dose of UVR_300nm. There was a slight increase of the intensity of forward light scattering on the contralateral side in animals that received 300 kJ/m². Altogether 72 Sprague-Dawley male rats were included. Half of the rats were exposed in vivo on one side to UVR_300nm. The other half was kept as a control group, receiving the same treatment as exposed rats but without delivery of UVR_300nm to the eye. Subgroups of the rats received either of the three doses. Rats were sacrificed at varying intervals after the exposure. The lenses were extracted and the forward light scattering was estimated. It is concluded that intensity of forward light scattering in the lens after exposure to UVR_300nm should be described with a continuous dose-reponse model.

This paper reports preliminary results of using Polysulphone to study scattered solar UV radiation underneath a shade cloth. Passive dosimeters, (Polysulphone) instead of a single UV meter were used to measure UVR-exposure to a selected target area on a minikin. Results show that the UV-dosimeters can be used to investigate the efficacy of shade structures without alteration of the field of solar radiation. The UV-transmittance of the shade cloth was measured to be 0.14. The ratio of the shaded dose to the unshaded dose at ten selected sites of the minikin was found to vary from 0.16 to 0.86 for the shade structure in the present experiments. A dosimetric model was proposed to estimate the effective dose to the facial area based on the measurement in five zones of the face. The result yields an 'average' ratio of the shaded dose to the unshaded dose of 0.31 as compared with the transmittance 0.14. They correspond to the protective factor of the shade structure by more than 100%. The possibility of including the effect of scattered radiation in the index for classification of UV-protective devices will be discussed.

When considering the degree of protection from erythema, afforded to humans by clothing materials, due to exposure to solar UV, the UV transmittance of the radiation over the spectral region 290 nm to 330 nm is considered. This can be expressed as the ratio of transmitted effective irradiance to the incident effective irradiance. We can define an effective UV blocking factor as one which is a function of the inverse of the transmittance and termed the `Ultraviolet Protection Factor' (UPF). In practical terms, the UPF factor will be determined from transmittance measurements of the materials. This paper reports the importance of a number of physical parameters eg. physical geometry factors such as material-to-detector distance, which need to be addressed in order to ensure that the assessment of solar UV transmittance through clothing materials provides a physically realistic determination, which translates consistently to an appropriate and technically correct UPF factor. In addition, a determination of the direct and indirect UV irradiance and transmittance components is presented.

Solar UV irradiance is measured in Westerland, Germany (54.9 degree(s) N, 8.3 degree(s) E) in the immediate vicinity of the North Sea shoreline. Measurements have been done since July 1993, focussing on the biologically effective UV radiation and the human body geometry. A grid double monochromator radiometer (DM 150, Bentham Instruments Comp., Reading, England) is used to measure the spectral resolution of 1 nm. Weighting the spectral irradiance by the action spectrum for the erythema is more appropriate for determining the biological effectiveness than simply dividing the UV radiation into the UV-A and UV-B wavebands. The erythemal irradiance shows a close relation to the sun angle during the course of a day. The exposure times, calculated from the irradiance and the minimal erythemal doses, suggest that people might underestimate the risk of getting sunburnt before noon. Diffuse radiation scattered from the sky contribute about 70% of the erythemal irradiance at a 45 degree(s) sun angle. A receiver oriented directly to the sun, i.e. 45 degree(s) inclined, receives an additional 30% of the erythemal irradiance measured by a horizontally adjusted cosine response sensor. The relative irradiance of curved surfaces like the skin is determined by UV- B-sensitive paper placed around a cylinder. This device detected UV radiation reflected by the sea, which hardly is measured by horizontally adjusted receivers.

An in vitro model of the well-known reaction of previtamin D photosynthesis in presence of UVB (280 to 315 nm) irradiation is proposed for the measuring of solar (and artificial) UVB radiation. The detailed study of the wavelength effect on the reaction kinetics using laser irradiation, as well as computer simulations, confirms the potential of the photoreaction as spectrally selective monitor of solar UVB. A method of express spectral analysis of the photoisomer mixture has been developed to promote realization of the proposal.

Recent developments in military systems aimed at protecting sensors and human eyes from battlefield laser threats can be applied to more traditional ultraviolet laser hazards. The technique involves utilizing a reflective optical system containing a sacrificial component that can act quickly enough to defeat ultra-short pulse length lasers. However, below a certain damage threshold the system level transmission can be as high as 90%. Laboratory safety equipment can be one of the beneficiaries of this technology since traditional filter based equipment can significantly reduce the visible spectrum. In addition, since this technology relies on energy rather than wavelength for attenuation, a single piece of safety equipment can be used with either frequency agile lasers or entirely different laser systems. The factor that makes this approach financially and technically feasible is the self-aligning reflective optical system technology employing single point diamond turning fabrication methods.

A method has been developed for determination of the biologically effective UV dose based on T7 phage as biosensor. In field experiments clockwork driven telescope has been used for determining doses from direct and global (direct plus diffuse) solar radiation. On fine summer days at mid-latitude this arrangement allowed the following comparisons: measured doses from direct and global radiation obtained at the same time and measuring site reflecting the biological importance of diffuse radiation; direct and global radiation obtained at the same time and measuring site reflecting the biological importance of diffuse radiation; direct and global doses obtained at the same time on different measuring sites (downtown, suburb, outside the town) reflecting the differences caused by air quality; direct and global doses obtained on the same measuring place, in summertime of two different years reflecting the importance of the long-term measurements for estimating the biological risk caused by increased UV-B radiation; measured data and model calculations.

The 193 nm excimer laser delivered through special tips into biological liquid environments was applied to two different fields of microsurgery and two mechanism of tissue ablation were found to be operative. In vitreoretinal surgical applications, where the tip exit diameter was about 250 micrometers , the effective cutting regime of retina and vitreoretinal membranes occurred at energy fluences of about 250 - 350 mJ/cm²/pulse with a corresponding cutting depth of 50 - 150 micrometers /pulse. Gas bubbles, formed at the tip exit when it touched the tissue during irradiation, seem to be the driving force underlying the cutting process. This enabled us to achieve a much deeper cut in tissue than a micron-sized laser penetration depth. The system was applied to bovine and rabbit retina and rabbit vitreoretinal membranes and it was found that such tissue removal is fast enough for real vitreoretinal applications and the cut depth control is still good enough for this microsurgery. In the application of this system to drilling of 4 - 8 micrometers diameter holes in the zona pellucida of oocytes the optimal energy fluence is about 40 mJ/cm²/pulse with an ablation depth of about 2 micrometers /pulse. In this case no bubbles are formed and the process seems to be a non-explosive photodissociation of the tissue with subsequent slow dissolution of the products. This mechanism, in contrast to the vitreoretinal tissue removal, was found to be very selective to the type of material being ablated. This process was studied on a model of 20% gelatin gel, which is very close to the ablation properties of the zona pellucida.

`Optical aging' of the lens of the eye results from the cumulative photochemical effects of ambient light exposures and may be exacerbated by any number of disease processes and exogenous agents including acute or chronic exposure to above- ambient levels of ultraviolet and/or blue light. This `optical aging' of the lens is manifested by increased scattering of visible light, increased absorption of short-visible wavelengths, and increased fluorescence emitted at short- to mid-visible wavelengths when irradiated with UV or blue light. With age and with or without exacerbating factors, the initially clear lens takes on an increasingly yellowish and ultimately brunescent coloration associated with cortical cataract. We conducted in vivo measurements of the lens fluorescence induced by UV and blue wavelengths. The fluorescence intensity was quantitated as a function of intensity of exciting light and excitation wavelength. It was shown that other `safe' blue laser exposures induced enough of a fluorescent veiling glare to imply interference with visual function. The visual deficit was objectively demonstrated by monitoring visual evoked potential amplitudes while subjects were irradiated with blue laser light. A related study demonstrated the utility of a prototype optical biopsy instrument as a diagnostic tool for assessing the optical properties of the lens. Optical signatures of individual lenses were characterized by compiling the backscatter and fluorescence spectra elicited by each of several exciting wavelengths. By examining the optical signatures of a population of approximately 100 human lenses, several metrics were chosen for gauging the optical quality of a given lens relative to the norm for the subject's chronological age. These metrics may serve to identify cases of accelerated `optical aging' and provide early evidence of cataract or other disease processes.

Research is being performed at several locations in consideration of learning the value of the front surface spallation process for tissue ablation. The experimental results are illustrating complicated features associated with the microscopic behavior of materials during the spallation process. This paper summarizes the current understanding of the spallation process in various materials and presents an interpretation of recent laser-tissue interaction experiments.

Temperature measurements of tissue during laser irradiation are typically made by thermocouples or thermal cameras. However, thermocouples are invasive and can affect the accuracy of measurements, whereas thermal cameras are constrained to surface measurements. Thus, there exits a need for an accurate, non-invasive temperature measurement technique within a tissue sample. We have used an interferometric technique to generate fringes from which temperature information is extracted.

The morphometrical analysis of the effect of a pulsed CO₂ laser on in vitro fresh rabbit vessel tissue was performed. The laser energy was delivered through a silver-halide fiber and the real time temperature was monitored via a second silver-halide fiber positioned on the external side of the irradiated tissue sample. In addition, a mathematical model was identified and applied on the analysis of the samples to quantify the internal temperature distribution. The model takes into account the dimension (coagulation, vacuolization) and the speed of the receding boundary between the ablated and normal tissue in a pulsed beam mode. Superficial hystological lesions were observed with ranges of energies of 20 msec/pulse, 1 Hz, 2 Hz, at 100 mJ, corresponding to a measured maximal external temperature range between 50 degree(s) and 60 degree(s)C. The used mathematical model has shown good agreement with these experimentally collected temperature measurements. Higher repetition rates for both 33 and 100 mJ/p were found to produce crater formation, in all the samples. The correspondent measured external temperatures were between 55 degree(s) and 95 degree(s)C and the calculated internal temperature of the injured layers were 142 - 306 degree(s)C, corresponding to the carbonization zones and depending on the type of tissue. The morphometrical analysis have shown: the CO₂ laser effect on the tissue is dependent on the angle of irradiation, the stereo metrical configuration and the water content of the irradiated tissue. A threshold value for injury generation is proposed.

It is widely agreed that a portion of the earth's protective stratospheric ozone layer is being depleted. The major effect of this ozone loss will be an increase in the amount of ultraviolet radiation (UV reaching the biosphere. This increase will be completely contained within the UVB (290nm - 320nm). It is imperative that assessments be made of the effects of this additional UVB on living organisms. This requires a detailed knowledge of the UVB photobiology of these life forms. One analytical technique to aid in the approximations is the construction of UV action spectra for such important biological end-points as human skin cancer, cataracts, immune suppression; plant photosynthesis and crop yields; and aquatic organism responses to UVB, especially the phytoplankton. Combining these action spectra with the known solar spectrum (and estimates for various ozone depletion scenarios) can give rise to a series of effectiveness spectra for these parameters. This manuscript gives a first approximation, rough estimate, for the effectiveness spectra for some of these bioresponses, and a series of crude temporary values for how a 10% ozone loss would affect the above end-points. These are not intended to masquerade as final answers, but rather, to serve as beginning attempts for a process which should be continually refined. It is hoped that these estimates will be of some limited use to agencies, such as government and industry, that have to plan now for changes in human activities that might alter future atmospheric chemistry in a beneficial manner.

This paper describes an analytical model for the heating of cellular material due to absorption of laser energy by individual melanin granules. Since melanin is the primary absorber of visible and near-IR light in the skin and in the retina, bulk heating of tissue might be determined by superposition of individual granule effects. Granules are modeled as absorbing spheres surrounded by an infinite medium of water. Model computations are quick and accurate. For short pulse exposures, the model predicts granular temperatures that far exceed the boiling point of water, which indicates that damage mechanisms may not be purely thermal. The goal is to include this model inside a larger one which predicts retinal injury by lasers, from ultrashort pulses to continuous wave.

We have established a neural network to quickly deduce optical properties of tissue slabs from the diffuse reflectance distribution. Diffusion theory based on multiple image sources mirrored about the two extrapolated boundaries is used to prepare the training and testing sets for the neural network. The neural network is trained using backpropagation with the conjugate gradient method. Once the neural network is trained, it is able to deduce optical properties of tissues within on the order of a millisecond. The range of the tissue optical properties that is covered by our neural network is 0.01 - 2 cm^-1 for absorption coefficient, 5 - 25 cm^-1 for reduced scattering coefficient, and 0.001 - 1 cm for tissue thickness. A separate network is also trained for thick tissue slabs. A simple experimental setup applying the trained neural network is designed to measure tissue optical properties quickly.