The ubiquity of laser radiation in military, medical, entertainment, telecommunications and research industries and the significant risk, of eye injury from this radiation are firmly established. While important advances have been made in understanding laser bioeffects using animal analogues and clinical data, the relationships among patient characteristics, exposure conditions, severity of the resulting injury, and visual function are fragmented, complex and varied. Although accident cases are minimized through laser safety regulations and control procedures, accumulated accident case information by the laser eye injury evaluation center warranted the development of a laser accident and incident registry. The registry includes clinical data for validating and refining hypotheses on injury and recovery mechanisms; a means for analyzing mechanisms unique to human injury; and a means for identifying future areas of investigation. The relational database supports three major sections: (1) the physics section defines exposure circumstances, (2) the clinical/ophthalmologic section includes fundus and scanning laser ophthalmoscope images, and (3) the visual functions section contains specialized visual function exam results. Tools are available for subject-matter experts to estimate parameters like total intraocular energy, ophthalmic lesion grade, and exposure probability. The database is research oriented to provide a means for generating empirical relationships to identify symptoms for definitive diagnosis and treatment of laser induced eye injuries.

Depiction of the cellular and immune responses in the human model is critical to design rational therapies preventing/limiting cellular destruction and ultimately functional visual loss following acute laser injuries. We report the light and electron microscopy histologic findings in a controlled ocular human laser exposure. Following informed consent, the normal eye of a patient scheduled to undergo exenteration for invasive carcinoma of the orbit was exposed to both continuous wave and Q-switched lasers. Four hours prior to exenteration, argon G lesions were placed in the superior/temporal quadrant and Nd:YAG lesions were placed in the inferior/temporal quadrant. After enucleation, the retina was prepared for routine light and transmission electron microscopy. Histology of the argon G lesions showed primarily photoreceptor and RPE photocoagulation damage. Neutrophil adhesion was limited within the choroid and no neutrophils were observed in the subretinal space. In contrast, the 4 hr Nd:YAG lesions showed extensive retinal disruption, hemorrhage within subretinal and intraretinal spaces, neutrophil accumulation in the retina, and an extensive neutrophil chemotaxic and emigration response in the choroid. Severe laser injuries elicit a significant neutrophil response by 4 hr, suggesting that neutrophils should be an early stage therapeutic target.

A 42 year old Caucasian female underwent uncomplicated extracapsular cataract extraction with posterior chamber lens implantation in the left eye, using a Zeiss model OpMi-6 operating microscope. Her postoperative course was unremarkable and she achieved a corrected visual acuity of 20/15+3. A lesion consistent with a photoretinal injury was noted inferior to the fovea. Seven months later the patient underwent cataract extraction in the right eye. Special care was taken to minimize light exposure during the procedure, including reducing the microscope illumination, minimizing operating time, intraoperative pharmacologic miosis, and using a corneal light shield. Despite these precautions, the patient developed a photoretinal injury almost identical to that in the contralateral eye. Postoperative corrected visual acuity was 20/15+3. Recent studies have reported incidences of retinal photic injuries from operating microscopes between 0 and 28 percent of patients. Several risk factors have been identified, including light intensity, intensity of the blue light component, and exposure time. The occurrence of a retinal photic injury in this patient despite precautions, development of bilateral cataracts at a young age, and a strong family history of early cataracts may indicate an inherited susceptibility to light induced damage. The American National Standards Institute is developing a product performance standard which will be applicable to operating microscopes used in ophthalmic surgery. The as yet undetermined role of individual susceptibility to retinal photic injury should be considered in the formulation of this standard.

Authors present two cases of macular burn caused by artillery laser rangefinder. Both injuries resulted form improper use of laser device. One of them occurred during combat activities. Safety goggles were not used. Macular burns resulted in permanent loss of central vision and visual acuity reduced to less than 0.1. Authors present results of clinical and functional tests made during long follow up period and comment similar published cases and ways of protection.

We evaluated retinal morphologic and visual functional changes in two individuals accidentally exposed to argon laser 'flashback' from an incorrectly placed laser protective filter while viewing a routine argon laser trabeculoplasty. These exposures, measured in the absence of a patient's eye, are in the region of the maximal permissible exposure. The patients were followed with serial visual function testing, scanning laser ophthalmoscopy (CSLO) and chromatic contrast sensitivity. The first individual received 54 monocular exposures. Acute examination revealed inferior and central Amsler grid abnormalities. These distortions matched the CSLO evidence of pigmentary changes in the corresponding retinal field. Initial contrast sensitivity showed high spatial frequency loss which increased during the ensuring 1.5 months. Chromatic contrast sensitivity revealed high spatial frequency loss for long wavelength test targets and broad spatial frequency loss with short wavelength targets. The second individual received fewer exposures bilaterally. Both eyes showed foveal morphologic alterations with non-selective changes in Moreland anomaloscopic matches, indicative of macular edema. We have shown a correlation between ophthalmoscopic and functional measures of spatial vision. Progressive loss in contrast sensitivity and spatial chromatic functional loss were associated with the more severe exposure while minimal changes were observed with fewer exposures.

The dose-response relationship for producing different grades of burns on skin produced by single Er-glass laser pulse were determined for energy densities within the range 0.5-35 J/cm² and pulse duration 100 ns and 2.5 ms. The persistent lesions on skin were subdivided into four morphologically different groups vs. radiant exposure of laser pulses. Histological investigation were made at 1- and 3-days post-exposure. Different methods of tissue preparation were tried to obtain better contrast of laser induced changes in skin tissue. At the 1-day post-exposure we observed on the histological samples coagulation of surface tissue, epidermis and dermis of skin depending on radiant exposure. 3-days histological samples revealed tearing of tissue detrit and active epitalization of damaged tissue.

We have used confocal scanning laser ophthalmoscopy (CSLO) to evaluate acute laser retinal injury in a small eye animal model. THe snake eye is optically unique, combining a high numerical aperture with a clear ocular media and a cornea covered with a hard dry spectacle. These optical qualities allow detailed resolution of photoreceptors, retinal nerve fiber, and retinal capillary blood cells in an intact vertebrate eye. We demonstrated that acute laser exposures capable of damaging the photoreceptor matrix may also alter blood flow at more anterior levels of the retina. Changes in photoreceptor density and orientation were indicated in the early post exposure seconds at high dose acute Argon laser exposures. An increase in photoreceptor reflectivity was observed in surviving photoreceptors and was enhanced with a near IR CSLO imaging source. Q-switched exposure failed to show this enhancement, possibly because of greater subchoroidal involvement associated with acoustic damage processes.

A body of data relates the ED₅₀ for laser-induced retinal damage to exposure duration for visible-wavelength laser exposure and for 1064 nm laser exposure. The database, extending from sub-nanosecond exposures to kilosecond exposures, can for the most part, be fit to models based on thermal interactions, thermal-mechanical mechanisms, and photochemical processes. Exceptions to this fit occur between 1 and 100 microseconds where the damage mechanism transitions from exclusively thermal to thermal-mechanical. Disagreement exists as to whether this anomalous dip of ED₅₀ is real or is an artifact of the data. We determined the laser-induced retinal ED₅₀ in Rhesus monkey eyes for several exposure durations from 12 nanoseconds to 1000 milliseconds at 755 nm using a dye laser, an alexandrite laser, and a Ti:Sapphire laser. These data do not show a dip in ED₅₀ in the microsecond time period.

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than one nanosecond. Laser minimum visible lesion thresholds for retinal damage from ultrashort laser pulses are produced at lower energies than in the nanosecond to microsecond laser pulse regime. We review the progress made in determining the trends in retinal damage from laser pulses of one nanosecond to one hundred femtoseconds in the visible and near-infrared wavelength regimes. We have determined the most likely damage mechanism operative in this pulse width regime and discuss implications on laser safety standards.

The recent development of ultrafast laser systems in the visible and near infrared spectral regions requires detailed knowledge of the material properties of ocular media. Different physical mechanisms play competing roles and give rise to new phenomena as the femtosecond laser pulse propagates in ocular media. We investigate the relative importance of radial diffraction and material dispersion for a wide range of wavelengths for femtosecond laser pulse propagation. Because no analytical solution exists which can fully explain the laser- material interaction, we use numerical techniques. The numerical technique will be described in detail.

Laser induced damage to the retina may produce immediate and serious loss in visual acuity as well as subsequent recovery of visual acuity over a 1 to 6 month post exposure period. While acuity may recover, full utilization of the foveal region may not return. In one patient, a superior/temporal preferred retinal location (PRL) was apparent, while a second patient demonstrated significant foveal involvement and contrast sensitivity more reflective of foveal than parafoveal involvement. These conditions of injury wee simulated by using an artificial scotoma technique which optically stabilized a 5 degree opacity in the center of the visual field. The transmission of spatially degraded target information in the scotoma was 0 percent, 5 percent and 95 percent. Contrast sensitivity for the 0 percent and 5 percent transmission scotoma showed broad spatial frequency suppression as opposed to a bipartite contrast sensitivity function with a narrow sensitivity loss at 3 cycles/degree for the 95 percent transmission scotoma. A PRL shift to superior temporal retina with a concomitant change in accommodation was noted as target resolution became more demanding. These findings suggest that restoration of visual acuity in human laser accidents may depend upon the functionality of complex retinal and cortical adaptive mechanisms.

Previously we have shown that visual deficits can be produced by long duration pulses at or slightly below traditional threshold levels for retinal injury. Initially the deficits produced were only transient shifts in baseline acuity that lasted less than 30 min, but successive exposures over a period of days at these same power levels were shown to be cumulative and their impact on visual acuity lengthened and became permanent. The present investigation extended these exposures to Q-switched, 532 nm Nd/YAG pulses presented to awake, task-oriented nonhuman primates performing Landolt ring discriminations. At and above the ED₅₀, single pulses of minimal spot diameter produced only minor, transient shifts in visual acuity while repeated exposures produced significant shifts in acuity that became permanent over time. At lower energies, minimal spot, single-pulsed exposures again produced little observable consequence until either retinal spot sizes or number of pulses were increased. At these lower energy levels, however, no permanent functional loss was observed. Hence, the functional impact of single Q-switched pulses was more difficult to assess than longer time domain exposures. Multiple, low level Q-switched pulses, and/or larger spot sizes produced visual deficits similar to those observed for msec time domain exposures, suggesting both temporal and spatial summation at energy levels where no permanent effects have been noted.

Seven Cynomolgus fasciculata who had graded laser lesions placed in own eye 6 years previously were evaluated for their vernier acuity by electrophysiologic recording techniques. In these experiments, 95 percent contrast vernier acuity targets were presented at high luminance levels to anesthetized primates. Visual evoked potentials were recorded by conventional means form scalp electrodes through hospital grade amplifiers. All animal testing was performed under IACUC approved protocols. The single q-switched pulses form a neodymium-YAG laser had produced lesions of 4 types: no visible change, minimal visible lesions, 'white dot' lesions and 'red dot' lesions in the eye at the time of placement. Single exposures had been made in four locations: 5 degrees superior, inferior and temporal to the fovea, and one foveally. Vernier recording proved somewhat successful in smaller animals with less than contained retinal hemorrhage lesions in the fovea. Initial analyses demonstrated a significant decrease of the pattern response signal/noise in the experimental eye overall, and an apparent relative loss of vernier signal in some lesioned eyes. Animals with the more severe lesions have somewhat degraded small patten responses and no recordable vernier response. Apparent lesser losses produced less effect.

The proliferation of lasers for medical care, laser displays, industrial applications and audio- visual presentations has increased the potential for accidental intrabeam exposure to visible laser radiation. The output of these laser devices may be limited to below permissible exposure limits, but they are perceived as bright and can affect performance. The disruption experienced while viewing a laser is related to factors that include the retinal irradiance level, wavelength, ambient light level and mode (continuous wave (CW) and repetitively pulsed (RP)). This report describes studies where these factors were varied to assess the effects of laser light on tracking performance in a laboratory simulator and in a field study. Disruption was determined by measuring maximum error and total time off target. Performance disruption increased as irradiance levels increased and ambient light levels decreased.Under dawn/dusk conditions, relatively low-level laser energy produced performance disruption. Green laser light at the peak of the photopic sensitivity curve was more disruptive than red laser light. Increased error scores during CW and RP trials were attributed to average rather than peak power effects. More than 1500 laser exposures at levels up to MPE/2 have been given to volunteers. Despite transient performance disruption comparison of the pre- and post- laser visual performance tests and fundus evaluations wee unremarkable.

In earth orbit, the ambient optical radiation environment provided by the sun is not the same as on the surface of the earth. The atmosphere provides a protective layer that is not present in space. The American Conference of Governmental Industrial Hygienists (ACGIH) has published guidelines for exposure to broad-band optical radiation. These guidelines are called threshold limit values (TLV). Potential hazards include photochemical and thermal effects on the eye and skin. These guidelines are intended to be used with artificial sources such as arc lamps, however, they may be applied to solar exposure during extravehicular activity so that recommendations may be made to limit the risk of astronauts who are spending more and more time outside the space shuttle. Protective filters are discussed that will limit exposure to optical radiation. Permissible exposure times are calculated based on the ACGIH TLVs. Although thermal TLVs may be exceeded, exposures are well below injury thresholds.

In the presence of atmospheric turbulence the nominal ocular hazard distance may no longer be a safe range for laser inter-beam viewing. Knowledge of the probability density function and standard deviation of the scintillations is essential for proper estimation of laser hazard level. Here we examine the probability of the minimum visible retinal lesion as a function of different forms of the scintillations distribution and standard deviation.

Radiant exposure of an Er-glass laser producing 50 percent probability (ED50) of a minimum erythema on porcine skin was measured in vivo for laser pulses 100 ns and 2.5 ms pulse duration. ED50 at 24 hours post-exposure was found 3.5 J/cm² for short laser pulses and 6.5 J/cm² for long ones. The single pulse dose in a chain of repetitive pulses producing minimum erythema were determined for 2ⁿ(n equals 16) pulses. The minimum reaction of skin on laser irradiance were studied for different beam diameter. The reaction of skin is mostly considered as local super heating. THe data obtained in the study are adequate to update safety standards for cutaneous injury.

Retinal laser photocoagulation treatments are often complicated with immediate side-effect of visual impairment. To determine whether glutamate-receptor blockers can serve as adjuvant neuroprotective therapy, we examined the effect of MK-801, an NMDA-receptor antagonist, on laser-induced retinal injury in a rat model. Argon laser retinal lesions were created in the retina of 36 DA rats. Treatment with intraperitoneal injections of MK-801 or saline was started immediately after the laser photocoagulation. The animals were sacrificed after 3, 20 or 60 days and the retinal lesions were evaluated histologically and morphometrically. Photoreceptor-cell loss was significantly smaller in MK-801-treated rats than controls. The proliferative membrane composed of retinal pigment epithelial cells which was seen at the base of the lesion in control retinas, was smaller in the MK-801-treated retinas. MK-801 exhibited neuroprotective and anti-proliferative properties in the retina. Glutamate-receptor blockers should be further investigated for serving as adjuvant therapy to retinal photocoagulation treatments.

Methylprednisolone have been demonstrated to ameliorate retinal photic injury. In the current study we examined its effect on laser induced retinal injury. Retinal lesions were inflicted by argon laser in 36 pigmented DA rats. The treated groups received intra-peritoneally methylprednisolone in saline, injected 3 times a day for 2 days, starting immediately after exposure. The controls received the vehicle on the same schedule. The rats were sacrificed 3, 20 or 60 days after laser exposure and the lesions were evaluated by light microscopy and morphometric measurements. Laser injuries were associated with disruption of the outer retinal layers. Three and 20 days after exposure, the loss of the photoreceptor-cell nuclei was significantly milder in the treated groups as compared with controls. There was no difference 60 days after exposure. In conclusion, methylprednisolone reduced temporarily the photoreceptor cell loss in argon laser induced retinal injury, when treatment was started immediately after laser exposure. There was no long term effect.

Adequate treatment strategies do not exist for retinal laser injuries. To gain a better understanding of available treatments, data form a variety of human laser accident cases and relevant experimental work was evaluated. Most laser eye injury cases are not attended by an ophthalmologist for several hours to days after injury and most patients are not treated.Of the few cases receiving treatment; only the FDA approved glucocortocoids are available for use. Their use, however, is still controversial. Experimental animal work during the acute phase of injury indicates that productive efforts have targeted neuroprotection, inflammation, ischemia- reperfusion, and lipid peroxidation. Late stage issues for treatment are scarring, retinal hole persistence and expansion, and traction. In summary, treatments for acute and late phase injury are currently inadequate. Preserving existing neural elements should be the top priority in these injuries. We recommend that relevant treatments begin immediately after injury. Other approaches are necessary to target early and late phase secondary damage events that are entrenched.

We designed, manufactured and field-tested new combat protection goggles which endow their users with optimal protection against ballistic injuries as well as against dust, sand and wind. A laser protection filter can be snapped on the ballistic goggles. Filters can be provided for any required wavelength. The goggles are of a warp-around shape ensuring peripheral as well as frontal protection. It is 'one size fits all' design with the least possible clearance between eye and lens so as to cause minimal interference with the use of optical equipment such as binoculars. There is an integral insert for prescription lenses inside the goggles. The head bands are self locking and putting the goggles on and off with or without a helmet on is easy.

In preparation for photodynamic therapy clinical trials, a research class IV argon ion-pumped dye laser was modified to allow delivery of laser radiation from the Laser Biology Research Laboratory (LBRL) to a surgical operating room (OR) located one floor below and over 50 meters away. Optical fibers and coaxial cable, protected by flame retardant conduit, were fed from the LBRL to the OR. A remote control box was constructed to allow physician control of the laser output from the OR. A safety-off and output-power control wee included in the control system. Safety issues involved calculations of maximum permissible exposure of OR staff to optical radiation, the classification of the laser output in the OR and dealing with the placement of relatively high-flux carrying optical fiber placed in utility chases. Operational considerations involved the calculation and measurement of optical transmission losses, the procedure for relaying operational status between the OR and laser facility and the necessity of conducting practice runs with the laser and OR staff.

An increased demand for advanced laser technology, especially in the area of cutaneous and cosmetic procedures has prompted physicians to use mobile laser services. Utilization of a mobile laser service allows physicians to provide the latest treatments for their patients while minimizing overhead costs. The high capital expense of laser systems is often beyond the financial means of individual clinicians, group practices, free-standing clinics and smaller community hospitals. Historically rapid technology turnover with laser technology places additional risk which is unacceptable to many institutions. In addition, health care reform is mandating consolidation of equipment within health care groups to keep costs at a minimum. In 1994, Abbott Northwestern Hospital organized an in-house mobile laser technology service which employs a group of experienced laser specialists to deliver and support laser treatments for hospital outreach and other regional physicians and health care facilities. Many of the hospital's internal safety standards and policies are applicable to the mobile environment. A significant challenge is client compliance because of the delicate balance of managing risk while avoiding being viewed as a regulator. The clinics and hospitals are assessed prior to service to assure minimum laser safety standards for both the patient and the staff. A major component in assessing new sites is to inform them of applicable regulatory standards and their obligations to assure optimum laser safety. In service training is provided and hospital and procedures are freely shared to assist the client in establishing a safe laser environment. Physician and nursing preceptor programs are also made available.

Organic dyes have found increasing use a s sensitizers in laser surgical procedures, due to their high optical absorbances. Little is known, however, about the nature of the degradation products formed when these dyes are irradiated with a laser. Previous work in our laboratories has shown that irradiation of polymeric and biological tissues with CO₂ and Nd:YAG lasers produces a host of volatile and semivolatile by-products, some of which are known to be potential carcinogens. This work focuses on the identification of the chemical by-products formed by diode laser and Nd:YAG laser irradiation of indocyanine green (ICG) and carbon black based ink sensitized tissues, including bone, tendon and sheep's teeth. Samples were mounted in a 0.5-L Pyrex sample chamber equipped with quartz optical windows, charcoal filtered air inlet and an outlet attached to an appropriate sample trap and a constant flow pump. By-products were analyzed by GC/MS and HPLC. Volatiles identified included benzene and formaldehyde. Semi-volatiles included traces of polycyclic aromatics, arising from the biological matrix and inks, as well as fragments of ICG and the carbon ink components. The significance of these results will be discussed, including the necessity of using appropriate evacuation devices when utilizing lasers for surgical procedures.

One of the major causes of anxiety in the dental clinic is the dental handpiece. Because dentists wish to provide a method which can replace the drill there has often been a premature use of the laser in dentistry. Various lasers have been introduced into the clinic before research has shown the laser used is of clinical benefit. Any new treatment method must not compromise the health of the patient being treated. Thus a method of evaluating the clinical abilities of dentists and their understanding the limitations of the laser used must be developed. Dentist must be trained in the basic interaction of the laser on oral tissues. The training has to concentrate on the variation of the laser wavelength absorption in the different tissues of the oral cavity. Because of the differences in the optical properties of these tissues great care must be exercised by practitioners using lasers on patients.

In laser surgery power densities of 10³ W/cm² are used for tissue vaporization or 10⁶ W/cm² and more for photoablation. These densities are harmful to endotracheal tubes or other devices which are used in a close distance to the laser beam. The laser resistance of endotracheal tubes was measured under the exposure of various lares in the UV, the visible and the IR wavelength range. The laser induced temperatures of the tube materials were measured by an IR camera. It is discussed which physical processes of light material interaction cause heat and how this heat deposition is compensated by cooling processes to keep the temperature rise in an acceptable range. The experimental observation can be well described by the physical properties of the materials and their composition.

Loss of foveal vision from exposure to laser light or retinal disease can seriously impair visual functions like reading and visual search. Central scotomas produce large losses in visually guided performance because central vision has the best visual resolution, compared to more peripheral retina, and is also important in the normal reflexive patten of eye movement. Relatively small central field scotomas can produce significant impairments in visual search if tasks require a high degree of foveal vision such as seeing fine detail or discriminating similar contours or letters. Subjects faced with the task of adapting to the loss of ventral vision sometimes position their eyes in ways which are either asymmetrical, not optimum, or seem to generate abnormal eye movements, even after extensive practice. Discussion includes oculomotor drift, error fixations, hyper-eccentric fixations and remedial eye positioning strategies.