Multi-element, multi-media method for the determination of airborne elemental emissions by inductively coupled plasma atomic emission spectrometry

BACKGROUND AND OBJECTIVE: A number of lasers are available for cutaneous periorbital surgery, yet not all eye shields are appropriate for all applications. We tested a variety of commercially available eye shields to assess their safety features. STUDY DESIGN/MATERIALS AND METHODS: Six commercially available eye protectors were studied. A focused laser was incident upon the shield, and the intensity and exposure duration required for visible damage to the shield were measured. We then measured the temperature on the underside of the eye shield during exposure from the laser. Time-dependent temperature measurements were made with a type-T thermocouple fixed to the eye shield with silicon grease. RESULTS: Thermal response curves and rates of warming for each of the six eye shields were generated. Plastic shields showed significant thermal damage with most of the lasers tested. The metallic shields warmed more slowly and to a lesser degree. CONCLUSION: Overall, the metallic eye shields had the most acceptable safety profile. Many of the plastic shields exhibited significant thermal damage, and therefore we discourage their use in periorbital laser surgery.     

Effects of ArF:excimer laser irradiation on human enamel and dentin

Round enamel and dentin surfaces of sound and carious extracted human teeth were irradiated by an ArF:excimer laser for up to 180 sec. Thermographic measurements indicated that the temperature rise due to heat accumulation caused by laser irradiation on these enamel and dentin surfaces was up to 19 degrees C (10 HZ with 540 J/cm2), and the temperature returned to the preirradiation value within 10 sec after the irradiation was stopped. Under light microscopy, no carbonization was evident on these surfaces, and a simple recess was formed by abrasion or vaporization in the irradiated regions. In the secondary SEM, uniformly distributed fine pores and prism structures appeared slightly on the enamel surfaces. Between the peritubular and the intertubular dentin, there appeared a distinct difference in the dissolved area. The laser almost completely removed carious regions of the enamel and the dentin, and penetration extended beyond the carious regions. In the backscattered electron SEM, highly mineralized layers were observed on the enamel and dentin surfaces dissolved by the laser.     

Calculation of retinal temperature distributions resulting from laser irradiation of the eye: I. Continuous lasers

The paper develops a simple analytic expression for the maximum temperature rise attained in the retina as a function of laser power, exposure duration, retinal absorption parameters and image radius. It is assumed that the laser beam has a Gaussian intensity distribution and is absorbed, following Beer's law, in both the pigment epithelium and the choroid layers of the eye. The final expression is mathematically accurate to 1% and is valid for image radii ranging from 20 to 500 mum and for exposure times from 30 ms to infinity. Consequently, this analysis is ideally suited to the interpretation of laser threshold damage experiments using shuttered gas lasers operated in their uniphase mode. Finally, the problem of defining a safe exposure level to laser radiation is considered. However, the lack of available information on minimum retinal image diameter and maximum absorption coefficient permits only an estimate of this parameter to be made.     

Application of Raney nickel to measure adducts of styrene oxide with hemoglobin and albumin

BACKGROUND: Although peripheral cryotherapy decreases the incidence of unfavorable anatomic outcomes in threshold retinopathy of prematurity (ROP), apnea, bradycardia, and lid edema can occur. Argon laser indirect ophthalmoscope photocoagulation has been used as an alternative to cryotherapy, with fewer adverse effects. Retinal lesions placed with diode lasers are deeper than similar argon laser lesions, and it is not known whether this difference could influence the response to ablative therapy. METHODS: Patients were enrolled under a prospective, randomized protocol. One eye of each patient with symmetric, threshold ROP was treated with an 814/815 nm diode laser, while the other eye was treated with cryotherapy. Patients with asymmetric diseases also were randomized for treatment in the threshold eye. RESULTS: Nineteen infants (33 eyes) were treated, ranging from 485 to 863 g birth weight (23 to 27 weeks gestational age); 18 patients (32 eyes) were followed for 3 months or longer. Four patients (8 eyes) had bilateral zone 1 disease. Postconceptional age was 36 to 45 weeks at the time of treatment. The diode laser treatment was better tolerated than cryotherapy, and the treatment apparatus was more easily transported. Apneic episodes requiring intubation resulted from two cryotherapy sessions but no diode laser sessions. Five cryotherapy-treated eyes required retreatment because of persistent disease with adjacent skip areas. In the group followed for 3 to 15 months, 1 cryotherapy-treated eye and 1 diode laser-treated eye progressed to stage 5 retinal detachment. CONCLUSION: Compared with cryotherapy, the diode laser was more convenient, technically easier to administer, and better tolerated by the patient. Although the number of patients was too small for meaningful statistical analysis of outcome, diode laser peripheral retinal ablation appeared to be as effective as cryotherapy for the treatment of threshold ROP.     

Probabilistic laser safety: ocular damage models for Q-switched neodymium and ruby lasers

International standards for the protection of the eyes from the hazards of laser radiation define a nominal ocular hazard distance as a distance beyond which an individual would not be expected to suffer any adverse biological effects. The nominal ocular hazard distance, and any associated hazard zones, are calculated using a deterministic technique. This technique does not consider the likelihood that an eye will be irradiated, or the probability that if any eye is exposed, then some level of ocular damage will result. An alternative method of hazard assessment, without compromising safety, is to adopt a probabilistic approach in which the ultimate safety criterion is that the expectation of someone receiving ocular damage must be less than some acceptable risk level. An important element in this assessment is an ocular damage model, which predicts the probability with which a laser exposure will cause permanent eye damage. This paper describes a rationale for the use of the minimum ophthalmoscopically visible lesion as a threshold criterion for the development of ocular damage models. A brief review of existing ocular damage threshold data for Q-switched neodymium:YAG and ruby lasers is presented, and ocular damage models for these lasers systems are derived.     

Effect of commercial dilating agents on laser flare-cell measurements

OBJECTIVE: To compare the effect of tropicamide alone and tropicamide-phenylephrine on anterior chamber flare and cell measurements obtained with a laser flare-cell meter. DESIGN: Prospective study. SETTING: Gimbel Eye Centre, Calgary. SUBJECTS: Twenty white subjects (10 with blue irides and 10 with brown irides) aged 24 to 45 (mean 30.2) years without any known systemic or ocular disease. INTERVENTIONS: Laser flare-cell measurements were obtained 30 minutes after pupillary dilation with 1% tropicamide in one eye and a combination drop of 0.8% tropicamide and 5% phenylephrine in the other eye. The average of five readings was taken for each eye. OUTCOME MEASURES: Flare and cell measurements. RESULTS: There was no statistically significant difference in flare photon count or cell count between the eyes dilated with tropicamide and those dilated with tropicamide-phenylephrine. In addition, iris colour was not found to have a significant effect on flare and cell measurements. CONCLUSIONS: Our results suggest that pupillary dilation for laser flare-cell measurements can be done with either mydriatic agent in healthy white subjects of any eye colour without significant effects on the measurements. Further study is needed to determine whether the same is true in older subjects.     

Effects of various laser types and beam transmission methods on female organ tissue in the pig: an in vitro study

The purpose of this in vitro study was to investigate and compare effects of various laser types (CO2, Argon, Erbium:YAG, Erbium:YSGG, and Holmium:YAG) and laser beam transmission methods (optical lens and flexible fiber) on ovarian and uterine tissue of the pig. The Erbium laser radiation was transmitted through Zirconium fluoride fibers (ZrF4). To circumvent the low mechanical stability of these fibers, we developed a special microlens system, which refocuses the radiation and protects the distal end from damage. Tissue lesions were performed with 1 and 5 joule. Histologic analysis of acute Er:YAG laser lesions reveal precise cutting effects with a minimal thermal damage zone of 40 microns and a high damage resistance of the fiber microlens systems. The extent of thermal damage caused by the Erbium:YSGG and CO2 laser is about two times larger, whereas the Argon and Holmium laser tissue lesions show a damage of the surrounding tissue of 200-300 microns. This study suggests that for precise cutting and coagulation, Erbium and Holmium lasers transmitted via our modified fiber tip may render the use of these lasers possible in a wide range of laparoscopic surgery applications.     

Responses to a postal survey on women''s health after birth: importance of repeated mailings and characteristics of non-respondents

The simulation of breast fields using an isocentric set-up technique can be a lengthy process involving the placement of the isocentre, the determination of the gantry angles, and the selection of the lung shields, which in our center is one of six standard blocks. We show that with a body contour taken through central axis, five measurements and a calculator program, it is possible to significantly decrease the amount of time required to simulate a breast patient. We have developed a program for an HP48GX handheld calculator to determine the gantry angles, the isocentre, the field width, the standard angled block, and the couch and collimator rotation. The calculations are based on measurements of the field length, the horizontal distance between midline and mid axillary line, and the vertical distances from the mid axillary line to the inferior and superior beam border and central axis at midline. We use spherical geometry to perform the calculations to reflect the true environment and do not make any assumptions about the average patient's shape. For the simulation process a jig was developed that is inserted into the tray holder of the simulator to show the optical and radiological shadow of the calculated shielding along the patient's midline for clinical assessment during simulation and on the simulation film. The jig also has a holder for an aluminum wedge to improve the image quality of the simulation film. We admit that the lung shield increases the dose to the contralateral breast because of increased scatter and transmission through the shield; however, the block decreases the volume of irradiated lung while keeping the beam edge along the midline of the patient. The technique has been in use for two years and has resulted in time savings of up to 30% per patient. It has proven to be an easy and accurate way of setting up isocentric treatments to the breast.     

IgA class serum antibodies against three different Klebsiella serotypes in ankylosing spondylitis

BACKGROUND: Over the past decade, the 585-nm pulsed dye laser (PDL) has been used successfully to treat a variety of cutaneous vascular lesions as well as hypertrophic scars. Laser scar revision has been revolutionized by the recent development of high-energy, pulsed carbon dioxide (CO2) laser systems. These new CO2 lasers allow controlled vaporization of thin layers of skin while minimizing damage to surrounding dermal structures. OBJECTIVE: To determine the effect of a high-energy, pulsed CO2 laser alone and in combination with a 585-nm PDL on nonerythematous hypertrophic scars. METHODS: Twenty patients with nonerythematous hypertrophic scars were treated with a high-energy, pulsed CO2 laser. One-half of each scar was additionally treated with the 585-nm PDL laser. Sequential clinical and photographic analyses were performed independently by two blinded assessors. In addition, erythema reflectance spectrometry measurements were obtained from the scars before and at regular postoperative intervals. RESULTS: Global assessment scores and erythema spectrometry measurements were significantly improved after laser treatment. Combination CO2 and PDL laser treatment resulted in more significant improvement than CO2 laser irradiation alone. CONCLUSION: Concomitant use of the high-energy, pulsed CO2 and PDL laser systems was superior to CO2 laser vaporization alone for revision of nonerythematous hypertrophic scars. Once again, the vascular specificity of the 585-nm PDL has been linked to improvement in hypertrophic scar tissue.     

Photocoagulation of well-defined choroidal neovascularization in age-related macular degeneration: clinicopathologic correlation

PURPOSE: To present the clinicopathologic features of the eyes of a patient with age-related macular degeneration (ARMD): the right eye was treated for well-defined extrafoveal choroidal neovascularization (CNV), and the left eye had an untreated disciform scar. METHODS: The patient was studied ophthalmoscopically and by fluorescein angiography at the time of presentation and on follow-up examinations up to 54 days after laser treatment, when he died. The posterior portions of both eyes (obtained postmortem), including the macula and optic nerve head, were sectioned serially for light microscopy. Tissue sections from both eyes were removed from glass slides and studied by transmission electron microscopy. RESULTS: Histopathologic study of the right eye disclosed a thin layer of basal laminar deposit throughout the posterior pole. Two defects in Bruch's membrane without CNV were present within the area of laser photocoagulation located superior to the fovea. No CNV was present in the scar. Eleven areas of early CNV were present in the posterior pole. Histopathologic study of the left eye showed a prominent basal laminar deposit throughout the posterior pole. A 2.6 x 2.7 mm disciform scar was present that was located mostly in the subretinal space. Four sources of CNV were present. CONCLUSIONS: The clinicopathologic features of a treated eye with well-defined extrafoveal CNV, and the fellow eye with a disciform scar, both associated with ARMD, are presented. Although laser treatment obliterated a choroidal neovascular membrane, 11 additional areas of early, subclinical CNV were present.     

Videographic and histologic comparison of Nd:YAG and diode laser contact transscleral cyclophotocoagulation

We performed contact transscleral cyclophotocoagulation in two human autopsy eyes with continuous-wave Nd:YAG and diode lasers. Duration of exposure was two seconds, and powers were 4 to 7.3 W with the Nd:YAG laser and 1.75 to 2.5 W with the diode laser. In both procedures, we used hand-held quartz fiberoptic contact probes for energy delivery. Tissue responses were viewed with high-magnification videographic recording technique to analyze the real-time laser effects. The treated tissues were then studied by light microscopy. We observed different tissue responses both videographically and histologically. Nd:YAG laser lesions were characterized by prominent tissue whitening and contraction of the ciliary epithelium, while the diode laser lesions had less whitening and the tissue contraction appeared to be deeper in the ciliary body. The histologic correlate was coagulation and disruption of the ciliary epithelium and little effect on the underlying ciliary muscle with the Nd:YAG laser, while the diode laser had less effect on the ciliary epithelium but caused a significant coagulative response in the ciliary muscle. Comparative trials are needed to establish the clinical significance of these videographic and histologic observations.     

Classification of laser irradiation and safety measures

The use of lasers in medicine and especially surgery is rapidly expanding in many disciplines from clinical laboratory to the office practice and operating room. It is essential that users of this powerful tool have knowledge of their potential hazards and the measures to protect patients and personnel against injuries or undesired effects. Below, we have included information about the way lasers are classified; the development of protective standards; the current status of protection standards that apply to lasers, especially those used in medicine/surgery; the specific kinds of hazards associated with medical/surgical applications; and the measures by which hazards have been controlled. Since laser technology is still a young field, it is likely that problems unknown at present will occur and methodologies for controlling hazards will evolve. The American National Standards Committee produced the first consensus standard Z136.1 in 1973. The Standard was revised in 1976 to accommodate differences in biological effects for different wavelengths in the visible spectrum. The ANSI Standard has been revised again in 1980, and currently (1984) there are two additional standards in preparation, Z136.2 and 136.3, which treat the safe use of light-emitting diodes and the safe use of lasers in the health care environment, respectively. Most surgical and medical lasers are Class III or IV. Some lasers have a Class IV therapy level beam plus a Class I or II alignment beam. When using lasers, it is possible to generate incandescence or fluorescence in an irradiated object. This can occur even with protective eyewear, because the correlated radiations are usually of a different wavelength. Generally, this should not be a problem when beams are directed at biological material. However, hazard could be caused by lasers designed to produce fluorescence. Control of correlative radiation in a laser system is required in the federal regulations. Hazards of lasers may be grouped as those to the eye, skin and associated hazards, fire, x-rays, electrical, fumes, toxic materials, etc. Effects on tissue are governed by the following factors:--the energy or power density of the beam;--the absorption in tissue at the laser wavelength;--the time the beam is held at a given area.;--the protective effects of heat removal by thermal conduction and by circulation. Eye hazards include thermal burns or acoustical disruption (shock waves) from high-powered or high-energy beams in the visible and near infrared wavelengths. Direct beam exposure or specular or diffuse reflaction from these very high-power lasers can also cause injuries to other parts of the retina. For example, beams can directly penetrate through the sclera and cause retinal injury. Near ultraviolet (less than 400 hm) and far infrared (.3000 hm including CO2 lasers) can cause moderate to severe corneal burns. Far ultraviolet (200-315 nm), mid infrared (1400-3000 nanometers) can cause welders' flash or snow blindness and chronic exposure could cause cataract, and exposure to ultraviolet rays may be carcinogenic. For CO2 lasers, the far infrared radiation is attenuated by plastic goggles, or by glasses, or quartz. Other eyewear with special filters is used for different lasers. The whole personnel who may be exposed to direct beams, specular reflections, and many times diffuse reflections must wear protective eyewear. In all cases the surgeon and others viewing the procedure through the endoscope need glasses or suitable protective lenses installed in the endoscope. Persons who are not viewing the beam may not need to wear protective glasses with the same level of optical density. Glasses may be selected to provide protection for lasers operating in the visible wavelength to the point where the normal aversion response could protect the individual.     

PMS after 40: persistence of a stress-related symptom pattern

BACKGROUND AND OBJECTIVE: Various yellow light lasers have been used over the past decade in an attempt to eradicate facial telangiectasia. Based on their power output, spot size, and pulsing characteristics, these lasers belong to one of two categories that exist at either end of a spectrum--high power, short pulse, and large spot size, or low power, long exposure, and small spot size. The copper bromide laser clearly belongs in the latter group, but with higher available power than most other lasers in this group, it exists further along the spectrum toward the region in which the laser parameters might be considered closer to theoretical ideals for treating certain cutaneous vascular pathologies. The objective of this study was to ascertain the role and efficacy of the copper bromide laser on treatment of a variety of facial telangiectasia. STUDY DESIGN/MATERIALS AND METHODS: A total of 570 patients with facial telangiectasia of different diameters and on different regions of the face were treated with the copper bromide laser one or more times and followed up over 5 years. RESULTS: More than 75% clearance was achieved in 70% patients, 50-75% clearance in 17.4% patients, and < 50% clearance in 12.6% patients. Poor results were correlated with anatomical location on the nasal alae and nasal tip and also with vessel size. Very small (< 100 microns) and very large (> 300 microns) vessels did not respond as well as vessels in the 100-300-micron diameter group. Very large vessels responded better to a combination of sclerotherapy and laser treatment. There were no reported long-term adverse effects. CONCLUSION: The copper bromide laser is a safe and effective modality for the treatment of the majority of facial telangiectasia. It is less suited to treating very small vessel lesions such as diffuse erythema, and conversely very large vessels as well as those of the nasal alae. These latter two groups respond better and more permanently to combined sclerotherapy and laser treatment.     

The albedo effect on neutron transmission probability

Shields, used for protection against radiation, are often pierced with vacuum channels for passing cables and other instruments for measurements. The neutron transmission through these shields is an unavoidable phenomenon. In this work we study and discuss the effect of channels on neutron transmission through shields. We consider an infinite homogeneous slab, with a fixed thickness (20 lambda, with lambda the mean free path of the neutron in the slab), which contains a vacuum channel. This slab is irradiated with an infinite source of neutrons on the left side and on the other side (right side) many detectors with windows equal to 2 lambda are placed in order to evaluate the neutron transmission probabilities (Khanouchi, A., Aboubekr, A., Ghassoun, J. and Jehouani, A. (1994) Rencontre Nationale des Jeunes Chercheurs en Physique. Casa Blanca Maroc; Khanouchi, A., Sabir, A., Ghassoun, J. and Jehouani, A. (1995) Premier Congré International des Intéractions Rayonnements Matière. Eljadida Maroc). The neutron history within the slab is simulated by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) and using the exponential biasing technique in order to improve the Monte Carlo calculation (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco). Then different geometries of the vacuum channel have been studied. For each geometry we have determined the detector response and calculated the neutron transmission probability for different detector positions. This neutron transmission probability presents a peak for the detectors placed in front of the vacuum channel. This study allowed us to clearly identify the neutron channeling phenomenon. One application of our study is to detect vacuum defects in materials.     

Wound healing and soft tissue effects of CO2, contact Nd: YAG and combined CO2-Nd: YAG laser beams on rabbit trachea

Rabbit trachea was used as an experimental model to study tissue effects and healing of full-thickness tracheal lesions produced by CO2, contact Nd: YAG and combined, coaxial CO2-Nd: YAG (Combo) laser beams. Two power settings (10 W and 16 W) were used with CO2 and contact Nd: YAG lasers. Three different CO2/Nd:YAG power ratios (1:1, 1:2 and 1:4) and power settings (12 W 15 W and 16 W) were used with the Combolaser. Histological specimens for light and transmission electron microscopy were prepared immediately and 1, 3, 5, 7, 14 and 21 days postoperatively. The wound with the most precise and fastest healing was produced by contact Nd: YAG laser. CO2 laser produced a moderate amount of charring and the largest amount of coagulated tissue with a slightly prolonged healing period. In the acute phase, tissue defects produced by the Combolaser with power ratios 1:1 and 1:2 resembled the CO2 laser lesions but with slightly less charring. The power ratio 1:4 diminished the cutting properties of the beam considerably. During the healing period the Combolaser produced the most intensive inflammation and granulation tissue formation resulting in delayed regeneration of the lesion. In transmission electron micrographs the most severe damage to chondrocytes was seen after using the Combolaser. These findings indicate that the Combolaser produces deeper tissue damage than CO2 or contact Nd:YAG laser. However, the Combolaser appears to be suitable for tracheobronchial operations, owing to its good simultaneous cutting and haemostatic properties.     

Types of medical lasers

The knowledge about different types of lasers and their potential use in medicine is presented. A very rapid development of laser technology in the world imposes a need for up-to-date information about the characteristics of different laser instruments. Without this kind of information it would be difficult to keep in touch with the latest developments in the world's technology. Different types of lasers have different indication range in the medical practice. An inquiry into the fundamental principles of lasers physics is an important prerequisite for successful application of this technology in medicine. Laser as a surgical knife has shown certain advantages over scalpel, electrocautery and cryosurgery, as the laser surgery is a noncontact method, bloodless, precise, with better visualization, minimal postoperative edema, painless healing, without complications. Although laser cannot entirely replace conventional surgical instruments, it is still the instrument of choice for treatment of numerous pathological conditions. The carbon dioxide laser is a highly precise, bloodless light scalpel used for incising and excising tissues and sealing small blood vessels. The infrared beam at 10,600 nm wavelength is absorbed by water and tissue destruction is due to the instantaneous vaporization at relatively low temperature of 100 degrees C. The beam seals blood vessels of up to 0.5 mm in diameter and if the beam is defocused, larger vessels may be controlled. The beam also seals lymphatics, possibly reducing the spread of tumour cells by this route, and seals nerve endings: there is no incidence of neuroma formation. Carbon dioxide laser has shown a great efficiency in otorhinolaryngology, in maxillo-facial surgery and plastic surgery, in urology and gynecology. Provides true "no touch" surgery, and is used increasingly in neurosurgery for the precise atraumatic removal of tissue and for creation of precise lesions for the control of pain. The carbon dioxide laser beam cannot, at present, be transmitted via a flexible fibre, although a number of fibres are being investigated. Delivery of laser energy to microscope, colposcope or handpiece is via an articulated arm which is a hollow tube with mirrors at the articulations. The argon laser produces blue-green coherent light at a number of wavelengts but 80% of the energy is at wavelengths of 488 and 514 nm. This laser was first used in ophtalmology to treat diabetic retinopathy through, and without damage to, the clear anterior parts of the eye. The argon laser is used for blood vessel coagulation but can be used to perform slow, thermal tissue destruction at higher power levels. Argon laser is most commonly used in ophthalmology for otological micro-surgery, particularly in the treatment of otosclerosis and tympanosclerosis. Very good results have been achieved in the argon laser treatment of gastrointestinal bleeding ulcers, vascular lesions and polyps. Dermatology is another field where argon laser has shown great efficiency: hemangyomas, telangiectasias, tattoos, small benign and malignant tumours are amenable to argon laser treatment. In neurosurgery it is used to control both normal and abnormal blood vessels but at present much work on treatment of arteriovenous malformations and aneurysms is experimental. Both the argon laser energy can be transmitted via flexible fibre optic delivery system which can then be attached to an operating microscope, slit lamp, endoscope delivery fibre or handpiece. The Neodymium-YAG laser is used both for tissue destruction with good haemostasis and for the control of normal and abnormal blood vessels. This laser produces infrared coherent light at 1060 nm wavelength, which is deeply absorbed in the tissues without colour or tissue specificity. Neodymium-YAG laser is mostly used in tracheobronchial, gastrointestinal and urologic pathology in the treatment of stenoses, granulomas, benign tumours, and for reduction of malignant tumours. (ABSTRACT TRUN     

Effect of ambient solar ultraviolet radiation on incidence of squamous-cell carcinoma of the eye

BACKGROUND: We have investigated the geographic distribution of squamous-cell carcinoma of the eye to assess whether solar ultraviolet light is a risk factor for this disease. METHODS: We used routinely collected population-based cancer incidence data and published measurements of ambient solar ultraviolet light in our analysis. FINDINGS: The incidence of squamous-cell carcinoma of the eye declined by 49% of each 10 degrees increase in latitude (p < 0.0001), falling from more than 12 cases per million per year in Uganda (latitude 0.3(0)) to less than O.2 per million per year in the UK (latitude > 50(0)). Solar ultraviolet radiation decreases with increasing latitude, and the incidence of squamous-cell carcinoma of the eye decreased by 29% per unit reduction in ultraviolet exposure (p < 0.0001). INTERPRETATION: Our results are compatible with the hypothesis that exposure to solar ultraviolet light is an important cause of squamous-cell carcinoma of the eye.     

Change in temperature of subjacent bone during soft tissue laser ablation

In tissues that closely approximate bone, sufficient heat may be transferred to the bone during laser surgery to cause damage and/or necrosis. To date, there have been few studies examining the temperatures elicited at the bone surface as a result of laser application to the overlying soft tissues. The purpose of this investigation was to determine, under in vitro conditions, temperature changes at the bone/soft tissue interface during laser ablation with CO2 and Nd:YAG lasers used with and without (w/wo) air/water coolant. Experimental specimens consisted of 5 mandibles from freshly sacrificed hogs; laser treatment sites were the buccal and lingual attached gingiva of the molars and the lingual keratinized mucosa of the incisor region. CO2 and Nd:YAG lasers were used w/wo coolant at power settings of 4 to 8 W and 5 to 9 W, respectively. Temperature changes were measured with a copper constant thermocouple contained within a 21 gauge hypodermic needle. In comparing the lasers at comparable energy densities w/wo coolant, temperature increases at the bone/soft tissue interface ranged from 8.0 to 11.1 degrees C with the Nd:YAG and 1.4 to 2.1 degrees C with the CO2. Similarly, in comparing the times required for the interface to return to baseline temperature following removal of the laser, values ranged from approximately 143 to 205 and approximately 119 to 139 seconds for the Nd:YAG and CO2, respectively. Results from this study suggest that, at energy densities equal or above those reported here, the increase in temperature at the bone surface as a result of periodontal soft tissue surgery with the Nd:YAG laser could be damaging, especially if the exposure is prolonged.     

Melanoma x macrophage fusion hybrids acquire increased melanogenesis and metastatic potential: altered N-glycosylation as an underlying mechanism

BACKGROUND AND OBJECTIVE: The aim of this study was to assess CO2 laser ability to eliminate bacteria from titanium implant surfaces. The changes of the surface structure, the rise in temperature, and the damage of connective tissue cells after laser irradiation were also considered. STUDY DESIGN/MATERIALS AND METHODS: Streptococcus sanguis and Porphyromonas gingivalis on titanium discs were irradiated by an expanded beam of CO2 laser. Surface alteration was observed by a light, and a scanning electron, microscope. Temperature was measured with a thermograph. Damage of fibroblastic (L-929) and osteoblastic (MC3T3-E1) cells outside the irradiation spot and adhesion of the cells to the irradiated area were also estimated. RESULTS: All the organisms (10(8)) of S. sanguis and P. gingivalis were killed by the irradiation at 286 J/cm2 and 245 J/cm2, respectively. Furthermore, laser irradiation did not cause surface alteration, rise of temperature, serious damage of connective tissue cells located outside the irradiation spot, or inhibition of cell adhesion to the irradiated area. CONCLUSION: CO2 laser irradiation with expanded beam may be useful in removing bacterial contaminants from implant surface.     

Interaction between infrared radiation and vitreous substitutes

OBJECTIVE: To characterize the interaction between midintrared radiation of cutting lasers used or proposed for vitreoretinal surgery and fluid vitreous substitutes commonly used in vitreoretinal surgery. METHODS: Optical transmittance of vitreous substitutes was measured with a double-beam spectrophotometer. Measurements were performed in a wide spectral range of infrared radiation, including the 2120-nm wavelength of the holmium-YAG laser and the water absorption peaks at 1440, 1930, and 2940 nm. RESULTS: The wavelengths considered have a penetration depth varying from 410 to 1 microns in Ringer's solution, balanced salt citrate-buffered solution, balanced salt bicarbonated-buffered solution, hyaluronate sodium, and hydroxypropyl methylcellulose ophthalmic solution, from 2000 to 13 mm in perfluorocarbon liquid, and from 52 to 2.5 mm in silicone and fluorosilicone oils. CONCLUSIONS: Midinfrared optical radiation exhibits dramatic differences of penetration depth in different vitreous substitutes. High-absorbing liquids should be used mainly with contact laser procedures and could provide a shield for remote structures. Low-absorption vitreous substitutes allow noncontact laser surgical procedures, but they also may cause direct optical damage to remote tissues. The knowledge of wavelength transmittance of vitreous substitutes is necessary to evaluate and optimize the efficacy and safety of cutting laser sources.