Radiant Exposure Levels Research Articles

Possibilities of Increasing the Role of Railways in the Public Transport System of the Urban Functional Area of Olsztyn

The article presents the results of ageing tests with the use of laboratory light radiation tested according to the EN ISO 16474-2 standard for painting systems used in rolling stock. The influence of aging on such properties as gloss, colour and hardness, was determined using two different irradiance settings of the order of 60 W/m2 and 120 W/m2 for the wavelength 300÷400 nm and the same levels of radiant exposure. In addition, this study describes the most important information about laboratory aging tests with simulation of sunlight, temperature, moisture including rain, which are included in ISO standardised test methods. The influence of weather parameters has been described, in particular the influence of an increased dose of irradiance on the degradation of selected physicochemical properties of coatings and the possibility of the predicted ageing progress (changes in selected properties). The obtained results of laboratory tests allow to make certain assumptions regarding the increase of the dose of irradiance and thus the shortening of the laboratory testing time in the context of the assessment of the most desirable properties of the coating for a given application with the use of laboratory ageing tests.

Improvement on properties of experimental resin cements containing an iodonium salt cured under challenging polymerization conditions

ObjectiveThe use of resin cements in clinical practice entails photopolymerization through prosthetic devices, which precludes light penetration. The objective of this study was to modify experimental resin cements (ERCs) with diphenyliodonium hexafluorophosphate (DPI) in an attempt to improve chemical and mechanical properties of materials cured with reduced irradiance and final radiant exposure. MethodsA co-monomer base containing a 1:1 mass ratio of 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was prepared, with 1mol% of camphorquinone and 2mol% of ethyl 4-(dimethylamino)benzoate as initiator system. The resin was divided into 4 fractions according to the DPI concentrations (0, 0.5, 1 and 2mol%). The challenging polymerization condition was simulated performing the light activation (12, 23 and 46s) through a ceramic block (3mm thick). The irradiance was assessed with a calibrated spectrometer (1320mW/cm2), resulting in three levels of radiant exposure (0.58, 1.1 and 2.2J/cm2). The polymerization kinetics was evaluated in real-time using a spectrometer (Near-IR). Water sorption and solubility was analyzed and the cohesive strength of resins obtained through the microtensile test. Polymerization stress was assessed by Bioman method. ResultsResins containing DPI had higher degree of conversion and rate of polymerization than the control (without DPI). The use of DPI reduced water sorption and solubility, and led to higher cohesive strength compared to resins without the iodonium salt. However, the stress of polymerization was higher for experimental resins with DPI. SignificanceEven under remarkably reduced irradiance, cements containing a ternary initiating system with an iodonium salt can present an optimal degree of conversion and chemical/mechanical properties.

Improved Ultraviolet Radiation Film Dosimetry Using OrthoChromic OC-1 Film†.

There is growing interest in far-UVC lighting, defined as wavelengths from 200 to 230 nm, because research has demonstrated these wavelengths to be an effective antimicrobial technology while posing a minimal hazard to human health. Far-UVC lighting is now being installed to directly irradiate spaces where humans are present, and it will be important to perform measurements to verify far-UVC lighting installations are operating within widely accepted exposure guidelines. In this work, we explore the use of a commercially available film, known as OrthoChromic OC-1, to measure ultraviolet radiation exposure. The film was tested with a variety of ultraviolet wavelengths and irradiance conditions, and the color change of the film was analyzed for increasing levels of radiant exposure. The film response extended over a dynamic range that was greater than the recommended exposure limits for far-UVC radiation so it can potentially be useful for health hazard monitoring. The spectrum of the incident ultraviolet radiation strongly affected the response of the film; therefore, for accurate measurements we recommend the measured spectrum match the spectrum used for calibration. Overall, dosimetry with this film provides a simple, accurate, and inexpensive method of quantifying ultraviolet radiation exposure that is suitable for far-UVC measurements.

Ignition of Welding Arc and UV Actinic Hazard Evaluation

Welding arcs emit strong ultraviolet (UV) radiation, which could pose serious health risks for skin and eyes. According to Directive 2006/25/EC, UV hazard evaluation has to be performed in the working environment. The measurement of welding arc ignition radiation is a difficult task. This article describes the effort made to determine actinic radiant exposure levels during welding arc ignition in the controlled environment of a welding laboratory. A new method of UV actinic hazard evaluation from welding arc ignition radiation using a CCD spectroradiometer combined with a photometer is presented. The hazard of UV emitted in pulsed metal active gas welding (MAG-P) of construction steel is described. The duration of ignition peak in the study was in the range of 9–15 ms. The actinic radiant exposure during arc ignition over aversion response time was in the range of 0.26–1.12 J/m2. The daily exposure time can easily exceed the permissible exposure time obtained in our study, i.e., 13–34 s, which means that UV radiation form MAG-P arc welding is hazardous for workers in the vicinity of the welding arc. The measurement method presented in the article enables determination of radiant exposure of arc ignition radiation.

Gold nanorod-assisted near-infrared stimulation of bullfrog sciatic nerve.

Infrared neural stimulation (INS) is a new and developing approach for neural repair, with the advantages of being non-contact, spatially precise, and artifact-free. However, the disadvantage of infrared light is that it is difficult to stimulate deep tissue because of its weak penetrating power. Therefore, this paper introduces an improved method using near-infrared laser to stimulate bullfrog sciatic nerves because of its strong penetrating power. Meanwhile, gold nanorods (Au NRs) are injected into the nerve to increase the absorption of light. The mechanism is the instantaneous temperature rise caused by the absorption of infrared light by Au NRs. The compound muscle action potential (CMAP) associated with the irradiated sciatic nerve is recorded by a multi-channel physiological signal instrument. The peak to peak amplitude (Vpp) of CMAP for sciatic nerves injected with Au NRs increases significantly compared to the CMAP for control nerves without Au NRs. These results demonstrate INS by labeling nerves with nanoparticle exhibiting latent capacity to increase the efficiency, spatial resolution, and the neural responsivity, and especially, can increase the penetration depth and reduce the requisite radiant exposure level.

Infrared Laser Light Elicits Cardiorespiratory Responses when Applied to the Nucleus Tractus Solitarius in the In Situ Rat Brainstem Preparation

The application of infrared laser (IR) light has been shown to alter central and peripheral neural activity. We hypothesized that cardiorespiratory activity would be an ideal system to test the effects of IR on spontaneous activity that is generated by a complex neural circuit. In the present study, we examined the responses elicited by IR stimuli delivered unilaterally to the intermediate subnucleus of the nucleus of the solitary tract (NTSINT) in the in situ brainstem preparation. The data show that IR light evoked changes in cardiorespiratory motor activity in a stimulus intensity‐dependent manner.These studies used the in situ arterially perfused brainstem preparation of male Sprague‐Dawley rat pups (P15–P25). We recorded outputs from the phrenic nerve, the cervical vagus nerve, and thoracic sympathetic nerve and monitored heart rate and perfusion pressure. A 200 mm optic fiber was positioned on the dorsal surface of the brainstem above the NTSINT. The IR light (1450nm) stimulus was 200 Hz pulse frequency, 200 ms pulses duration for 30 s. In order to gain an insight into the potential neurochemistry associated with the IR light‐induced responses, we also examined the effects elicited by the microinjection of the excitatory neurotransmitter, glutamate (20 to 30 nL of a 10 mM solution) into the NTSINT.Low radiant exposure levels of IR light stimuli (4.78 J/cm2 per pulse) decreased phrenic nerve activity (consistent with a decrease in breathing frequency), decreased bursting of vagal activity, inhibition of thoracic sympathetic nerve, a decrease in heart rate and a decrease in perfusion pressure. Upon cessation of IR light application was often followed by a post‐stimulus response. This delayed effect consisted of a further decrease in breathing rate, thoracic sympathetic bursting and perfusion pressure. Increasing the radiant exposure to 5.57 J/cm2 per pulse evoked a strong baroreflex‐like response but only during IR light stimulation. Further, increases in radiant exposure levels evoked the immediate effect, other behaviors like swallowing; and a post‐stimulus response (10 to 30 seconds) such increases in breathing frequency. However, the cardiorespiratory patterning had changed and returning to a 4.78 J/cm2 per pulse IR light stimulus did not evoked comparable response in cardiorespiratory patterning as before. The microinjections of glutamate into the NTSINT elicited cardiorespiratory responses that were similar to those elicited by the lower intensity IR light stimuli.These data indicate that the even though IR light stimuli are focally applied they are strong enough to elicit network effects on respiratory and sympathetic activities. The mechanisms by which IR light elicits these profound changes in cardiorespiratory circuit function remain to be elucidated.Support or Funding InformationGlaxoSmithKline (GSK) FundingCWRU Internal Number: RES510692

Violet 405-nm light: a novel therapeutic agent against common pathogenic bacteria

BackgroundThe increasing incidence of healthcare-associated infections (HAIs) and multidrug-resistant organisms demonstrate the need for innovative technological solutions. Staphylococcus aureus, Streptococcus pneumonia, Escherichia coli, and Pseudomonas aeruginosa in particular are common pathogens responsible for a large percentage of indwelling medical device-associated clinical infections. The bactericidal effects of visible light sterilization (VLS) using 405-nm is one potential therapeutic under investigation. Materials and methodsLight-emitting diodes of 405-nm were used to treat varying concentrations of S aureus, S pneumonia, E coli, and P aeruginosa. Irradiance levels between 2.71 ± 0.20 to 9.27 ± 0.36 mW/cm2 and radiant exposure levels up to 132.98 ± 6.68 J/cm2 were assessed. ResultsDose-dependent effects were observed in all species. Statistically significant reductions were seen in both Gram-positive and Gram-negative bacteria. At the highest radiant exposure levels, bacterial log10 reductions were E coli—6.27 ± 0.54, S aureus—6.10 ± 0.60, P aeruginosa—5.20 ± 0.84, and S pneumoniae—6.01 ± 0.59. Statistically significant results (<0.001*) were found at each time point. ConclusionsWe have successfully demonstrated high-efficacy bacterial reduction using 405-nm light sterilization. The VLS showed statistical significance against both Gram-positive and Gram-negative species with the given treatment times. The β-lactam antibiotic-resistant E coli was the most sensitive to VLS, suggesting light therapy could a suitable option for sterilization in drug-resistant bacterial species. This research illustrates the potential of using VLS in treating clinically relevant bacterial infections.

Synergistic combination of near-infrared irradiation and targeted gold nanoheaters for enhanced photothermal neural stimulation

Despite a potential of infrared neural stimulation (INS) for modulating neural activities, INS suffers from limited light confinement and bulk tissue heating. Here, a novel methodology for an advanced optical stimulation is proposed by combining near-infrared (NIR) stimulation with gold nanorods (GNRs) targeted to neuronal cell membrane. We confirmed experimentally that in vitro and in vivo neural activation is associated with a local heat generation based on NIR stimulation and GNRs. Compared with the case of NIR stimulation without an aid of GNRs, combination with cell-targeted GNRs allows photothermal stimulation with faster neural response, lower delivered energy, higher stimulation efficiency and stronger behavior change. Since the suggested method can reduce a requisite radiant exposure level and alleviate a concern of tissue damage, it is expected to open up new possibilities for applications to optical neuromodulations for diverse excitable tissues and treatments of neurological disorders.

Effect of High-Irradiance Light-Curing on Micromechanical Properties of Resin Cements.

This study investigated the influence of light-curing at high irradiances on micromechanical properties of resin cements. Three dual-curing resin cements and a light-curing flowable resin composite were light-cured with an LED curing unit in Standard mode (SM), High Power mode (HPM), or Xtra Power mode (XPM). Maximum irradiances were determined using a MARC PS radiometer, and exposure duration was varied to obtain two or three levels of radiant exposure (SM: 13.2 and 27.2 J/cm2; HPM: 15.0 and 30.4 J/cm2; XPM: 9.5, 19.3, and 29.7 J/cm2) (n = 17). Vickers hardness (H V) and indentation modulus (E IT) were measured at 15 min and 1 week. Data were analyzed with nonparametric ANOVA, Wilcoxon-Mann-Whitney tests, and Spearman correlation analyses (α = 0.05). Irradiation protocol, resin-based material, and storage time and all interactions influenced H V and E IT significantly (p ≤ 0.0001). Statistically significant correlations between radiant exposure and H V or E IT were found, indicating that high-irradiance light-curing has no detrimental effect on the polymerization of resin-based materials (p ≤ 0.0021). However, one resin cement was sensitive to the combination of irradiance and exposure duration, with high-irradiance light-curing resulting in a 20% drop in micromechanical properties. The results highlight the importance of manufacturers issuing specific recommendations for the light-curing procedure of each resin cement.

Violet 405 nm light: A novel therapeutic agent against β-lactam-resistant Escherichia coli.

Approximately 1.7 million patients are affected by hospital-acquired infections every year in the United States. The increasing prevalence of multidrug-resistant bacteria associated with these infections prompts the investigation of alternative sterilization and antibacterial therapies. One method currently under investigation is the antibacterial properties of visible light. This study examines the effect of a visible light therapy (VLT) on β-lactam-resistant Escherichia coli, a common non-skin flora pathogen responsible for a large percentage of indwelling medical device-associated clinical infection. 405 nm light-emitting diodes were used to treat varying concentrations of a common laboratory E. coli K-12 strain transformed with the pCIG mammalian expression vector. This conferred ampicillin resistance via expression of the β-lactamase gene. Bacteria were grown on sterile polystyrene Petri dishes plated with Luria-Bertani broth. Images of bacterial growth colonies on plates were processed and analyzed using ImageJ. Irradiance levels between 2.89 ± 0.19 and 9.45 ± 0.63 mW cm(-2) and radiant exposure levels between 5.60 ± 0.39 and 136.91 ± 4.06 J cm(-2) were tested. VLT with variable irradiance and constant treatment time (120 minutes) demonstrated significant reduction (P < 0.001) in E. coli between an irradiance of 2.89 mW cm(-2) (81.70%) and 9.37 mW cm(-2) (100.00%). Similar results were found with variable treatment time with constant irradiance. Log10 reduction analysis produced between 1.98 ± 0.53 (60 minute treatment) and 6.27 ± 0.54 (250 minute treatment) log10 reduction in bacterial concentration (P < 0.001). We have successfully demonstrated a significant bacterial reduction using high intensity 405 nm light. Illustrating the efficacy of this technology against a β-lactam-resistant E. coli is especially relevant to the need for novel methods of sterilization in healthcare settings. These results suggest that VLT using 405 nm light could be a suitable clinical option for eradication of β-lactam-resistant E. coli. Visible light kills statistically significant concentrations of E. coli. Antibiotic-resistant Gram-negative bacteria exhibits sensitivity to 405 nm light. Greater than 6 log10 reduction in β-lactam-resistant E. coli when treated with visible light therapy.

Radiant exposure level comparison between Gaussian and top hat beams in various scanning patterns

The radiant exposure of optical irradiation beams with different scanning parameters has been theoretically studied. We analyzed the difference in radiant exposure introduced by Gaussian and top hat beams. Various parameters such as scanning pattern, aperture position, beam size and scan spacing were also introduced in this study. We found that Gaussian beams introduce higher calculated radiant exposure to the aperture than top hat beams for certain beam size to aperture size ratios. However, as the scan spacing decreases, the radiant exposure difference calculated from Gaussian and top hat beams diminishes.

Porcine skin damage thresholds for 0.6 to 9.5 cm beam diameters from 1070-nm continuous-wave infrared laser radiation

There is an increasing use of high-power fiber lasers in manufacturing and telecommunications industries operating in the infrared spectrum between 1000 and 2000 nm, which are advertised to provide as much as 10 kW continuous output power at 1070 nm. Safety standards have traditionally been based on experimental and modeling investigations with scant data available for these wavelengths. A series of studies using 1070-nm infrared lasers to determine the minimum visible lesion damage thresholds in skin using the Yucatan miniature pig (Sus scrofa domestica) for a range of beam diameters (0.6, 1.1, 1.9, 2.4, 4.7, and 9.5 cm) and a range of exposure durations (10 ms to 10 s) is presented. Experimental peak temperatures associated with each damage threshold were measured using thermal imaging. Peak temperatures at damage threshold for the 10-s exposures were ∼10°C lower than those at shorter exposures. The lowest and highest experimental minimum visible lesion damage thresholds were found to have peak radiant exposures of 19 and 432 J/cm2 for the beam diameter-exposure duration pairs of 2.4 cm, 25 ms and 0.6 cm, 10 s, respectively. Thresholds for beam diameters >2.5 cm had a weak to no effect on threshold radiant exposure levels for exposure times ≤0.25 s, but may have a larger effect on thresholds for exposures ≥10 s.

Initial fracture resistance and curing temperature rise of ten contemporary resin-based composites with increasing radiant exposure

ObjectivesThe principal objective of this study was to determine whether the bulk fracture resistance of ten light activated composites varied over a clinically realistic range of radiant exposures between 5 and 40J/cm2. MethodsTen operators were tested for clinically simulated radiant exposure delivery from a Bluephase® (Ivoclar Vivadent, Schaan, Liechtenstein) LED light to an occlusal cavity floor in tooth 27 in a mannequin head using a MARC®-Patient Simulator (Bluelight Analytics Inc., Halifax, NS) device. Notch disc test samples were prepared to determine the torque resistance to fracture (T) of the composites. Samples were irradiated with the same monowave Bluephase® light for 10s, 20s or 40s at distances of 0mm or 7mm. After 24h, storage samples were fractured in a universal testing machine and torque to failure was derived. ResultsRadiant exposure delivered in the clinical simulation ranged from 14.3% to 69.4% of maximum mean radiant exposure deliverable at 0mm in a MARC®-Resin Calibrator (Bluelight Analytics Inc., Halifax, NS) test device. Mean torque to failure increased significantly (P<0.05) with radiant exposure for 8 out of 10 products. The micro-fine hybrid composite Gradia Direct anterior (GC) had the lowest mean (S.D.) T between 10.3 (1.8)N/mm and 13.7 (2.2)N/mm over the tested radiant exposure range. Three heavily filled materials Majesty Posterior, Clearfil APX and Clearfil Photo-Posterior (Kuraray) had mean T values in excess of 25N/mm following 40J/cm2 radiant exposure. Mean T for Z100 (3MESPE) and Esthet-X (Dentsply) increased by 10% and 91% respectively over the tested range of radiant exposures. ConclusionsIndividual products require different levels of radiant exposure to optimize their fracture resistance. Light activated composites vary in the rate at which they attain optimal fracture resistance. Clinical significanceUnless the clinician accurately controls all the variables associated with energy delivery, there is no way of predicting that acceptable fracture resistance will be achieved intra-orally.

Epidermal laser stimulation of action potentials in the frog sciatic nerve

Measurements of laser-stimulated action potentials in the sciatic nerve of leopard frogs (Rana pipiens) are made using two infrared lasers. The dorsal sides of the frog's hind limbs are exposed to short-pulsed 1540- and 1064-nm wavelengths at three separate spot sizes: 2, 3, and 4 mm. Energy density thresholds are determined for eliciting an action potential at each experimental condition. Results from these exposures show similar evoked potential thresholds for both wavelengths. The 2-mm-diam spot sizes yield action potentials at radiant exposure levels almost double that seen with larger beam sizes.

Light-Induced Retinal Changes Observed with High-Resolution Autofluorescence Imaging of the Retinal Pigment Epithelium

Autofluorescence fundus imaging using an adaptive optics scanning laser ophthalmoscope (AOSLO) allows for imaging of individual retinal pigment epithelial (RPE) cells in vivo. In this study, the potential of retinal damage was investigated by using radiant exposure levels that are 2 to 150 times those used for routine imaging. Macaque retinas were imaged in vivo with a fluorescence AOSLO. The retina was exposed to 568- or 830-nm light for 15 minutes at various intensities over a square (1/2) degrees per side. Pre- and immediate postexposure images of the photoreceptors and RPE cells were taken over a 2 degrees field. Long-term AOSLO imaging was performed intermittently from 5 to 165 days after exposure. Exposures delivered over a uniform field were also investigated. Exposures to 568-nm light caused an immediate decrease in autofluorescence of RPE cells. Follow-up imaging revealed either full recovery of autofluorescence or long-term damage in the RPE cells at the exposure. The outcomes of AOSLO exposures and uniform field exposures of equal average power were not significantly different. No effects from 830-nm exposures were observed. The study revealed a novel change in RPE autofluorescence induced by 568-nm light exposure. Retinal damage occurred as a direct result of total average power, independent of the light-delivery Because the exposures were near or below permissible levels in laser safety standards, these results suggest that caution should be used with exposure of the retina to visible light and that the safety standards should be re-evaluated for these exposure conditions.

Investigation of the irradiance-dependent spectral transmittance of laser filters in the nanosecond- and femtosecond-pulse regime in the wavelength range between 700 and 800 nm

Induced transmittance is observed with polycarbonate laser filters when they are irradiated by laser pulses with a width of 200 fs. These results are compared with measurements in the nanosecond time domain. Calculations by a simple absorption model show, that single photon absorption is dominating the light-matter interaction at the pulse widths used in this study, at least at radiant exposure levels at which the filter material is not damaged. The use of eyewear showing induced transmittance can lead to a risk for the user, if the filter is irradiated by a strong laser beam in an accident. This situation can be even worse when an additional temperature effect is taken into account, which shifts the transmittance characteristics to lower optical densities when the temperature of the laser filter is maintained at a lower level. An example for this effect is given for nanosecond-pulse laser interactions.

Noncontact Laser Photothermal Keratoplasty II: Refractive Effects and Treatment Parameters in Cadaver Eyes

Noncontact laser photothermal keratoplasty may provide a new alternative for the treatment of myopia, hyperopia, and astigmatism. The purpose of this article is to study the refractive effect that laser photoablation keratoplasty is capable of producing on a normal human cadaver cornea, including the relationship between the keratometric changes and laser treatment parameters. The human cadaver eyes were treated with a holmium laser (pulsed Ho:YAG, 2.10 microns, 250 microseconds) coupled to a maskable, polyprismatic delivery system mounted on either an optical bench or a slit-lamp microscope. Using a topographic videokeratography system, we first investigated the refractive effect that noncontact laser photothermal keratoplasty would produce on a normal cadaver cornea. We then studied the keratometric changes produced by different radiant exposure levels at a fixed treatment pattern, as well as by different treatment patterns at a fixed radiant exposure level. Finally, we studied the possible therapeutic application of laser photothermal keratoplasty for correcting high postoperative astigmatism on a cadaver eye model. For the single-pulse 3-millimeter ring of eight-spot treatment, the keratometric power of the cornea initially increased with the radiant exposure and peaked at 26 J/cm2. The refractive effect was increased by projecting an additional set of eight spots equidistant between the first eight spots on the same diameter ring. Eighteen J/cm2 was the minimal radiant exposure required to produce consistent and predictable keratometric changes. The corneas were flattened using treatment patterns smaller than or equal to 3 mm in diameter and steepened using treatment patterns larger than or equal to 5 mm in diameter. A transition zone between 4 and 5 mm was observed in which minimal and unpredictable keratometric changes of the central cornea occurred. The surgically-induced astigmatism (> 10.00 D) was corrected by progressive laser photothermal keratoplasty treatments. Laser photothermal keratoplasty can acutely steepen and flatten the cornea in human cadaver eyes.

Noncontact Laser Photothermal Keratoplasty III: Histological Study in Animal Eyes

Laser photothermal keratoplasty has been studied as a potential refractive procedure. The purpose of this study is to investigate the histological response to various laser treatments including geometrical patterns, radiant exposure levels, and pulse numbers. A noncontact laser photothermal keratoplasty system was used in this study. Epithelial and endothelial response to the laser photothermal keratoplasty annulus treatment pattern were studied on an owl monkey model with a 5-millimeter annulus ring pattern, 8 J/cm2, 25 consecutive pulses at 1 Hz. Epithelial and endothelial response to the laser photothermal keratoplasty spot pattern were then studied and compared on cat and rabbit models for safety monitoring. One pulse and five consecutive pulses of eight different radiant exposures (5.00 J/cm2 to 18.01 J/cm2) were applied on each cornea. A cadaver eye model was used to study the collagen shrinkage induced by the laser spot treatment following the same protocol as the cat and rabbit model. Finally, the biological healing response to the laser photothermal keratoplasty treatment with the optimal laser parameters obtained in our experiment was studied on the cat model. Five cats were treated by the laser photothermal keratoplasty procedure with eight spots on a 3-millimeter ring, 15.6 J/cm2, and 1 pulse. Epithelial and endothelial damage were observed after annulus treatment on an owl monkey's cornea at 8 J/cm2, 25 pulses, and after spot treatment on cat and rabbit corneas at 18.01 J/cm2, five pulses. No endothelial damage was observed on cat corneas for the single pulse treatment at 18.01 J/cm2. For the tissue shrinkage study, no laser photothermal keratoplasty lesion could be detected for a radiant exposure setting below 10.26 J/cm2. Histological cross-sections showed that the five-pulse treatment reached the endothelial layer at a radiant exposure of 13.4 J/cm2, while no single pulse treatment reached the endothelium for the radiant exposure range (5 J/cm2 to 18 J/cm2) studied. The cat model showed that the laser-induced mechanical octagonal stress-lines by collagen shrinkage were maintained after 3 months. The histological sections across the lesion showed a denser keratocyte population indicating scar formation. The volume of collagen shrinkage, its location, and its geometrical shape can be accurately and precisely controlled by a 2.10-micrometer Ho:YAG laser coupled to an optical delivery system.

Damage to the rainbow trout (Oncorhyncus mykiss) lens following an acute dose of UVB.

Rainbow trout (Oncorhynchus mykiss) were used to model the solar radiation-induced cataract that occurs in hatchery-reared lake trout (Salvelinus namaycush). Rainbow trout eyes were exposed to wideband predominantly UVB radiant energy from a filtered 1000W xenon source. Lenticular damage was assessed and classified and comeal damage noted. Lenticular threshold radiant exposure was 0.48 J.cm-2 which is in the same range as the mammalian lens. Permanent lenticular damage occurred at radiant exposure levels approximately twice the threshold for lenticular radiant exposure (also similar to the mammalian response). Slit-lamp and scanning electron microscopical results support the theory of post-exposure anterior subcapsular epithelial cell damage, lens fibre swelling, and eventual rupture, leading to areas of lower refractive index in the anterior subcapsular region of the lens.

UV-B radiation and the optical properties of cultured bovine lenses

The effect of UV-B radiation on the crystalline lens was examined by subjecting bovine lenses in culture to varying low exposures at 300 nm. Lens optical quality was monitored on a long-term basis (to 1000 hrs.) with an automated scanning laser system that recorded both change in relative scatter and focal length across each lens. Data were collected for 20 lens positions at each scan. Radiant exposure levels consisted of 0.5, 0.25, 0.125, 0.06 and 0.03 Jcm-2. Twenty irradiated lenses were compared to twelve untreated controls. All of the irradiated lenses showed changes in scatter and focal length relative to the controls. Most (about 75%) of the treated lenses showed significant increases in scatter (200-400%) and focal length (10-20%) at 40 to 60 hours after exposure. A similar time frame for lens damage was noted by visual inspection. Exposure to UV-B at the above doses did not affect culture longevity.