Ocular exposure to environmental light and ultraviolet--the impact of lid opening and sky conditions.
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Adult↗
Biomedical subjects
D H Sliney
Publications and source records attributed to D H Sliney.
Laser safety.
Safety has always been an important aspect of any laser application in surgery and medicine. In any review of the laser surgery literature, several issues continue to dominate. These issues include: wearing eye protectors, dealing with the plume of vaporized tissue, and controlling potential fire hazards. No one denies that lasers can pose a serious hazard to the eye, but the decision to wear eye protectors in all procedures has been frequently questioned. The degree of effort needed to minimize the very serious risk from chronic breathing of vaporized tissue also requires judgment. Aside from a few eye injuries from a laser beam exposure, most serious accidental injuries (and even deaths) reported to date from the laser beam itself can be traced to the ignition of surgical drapes and airway tubes.
Humans↗
UV radiation ocular exposure dosimetry.
There is currently some degree of controversy as to the magnitude of cataract and other ocular diseases related to human lifetime exposure to UV radiation (UVR). Concerns about the depletion of stratospheric ozone and the related increase in terrestrial UVR exposure have emphasized the importance of resolving this controversy. A careful study of ocular exposure to environmental sunlight demonstrates that it is not simple to determine accurately the level of solar UVR exposure of the human eye. Past attempts to measure or calculate UVR exposure of the eye have generally relied on the measurement of ambient UVR in sunlight with global monitors. Unfortunately, such attempts have seldom assessed properly the large role of ground reflection, the horizon sky contribution, the degree of lid opening and the extreme lateral component of UVR incident on the eye. A series of recent ocular dosimetry studies are described which have considered all of these factors. In addition, the value of different types of eye protection is shown to vary widely depending on the frame design. The dosimetry studies can be confirmed by a biological dosimeter--the human cornea. Because the action spectrum and threshold for human photokeratitis are well defined, the living cornea can serve as a biological dosimeter for ocular exposure.
Cornea↗
New stroboscopic light source for intraoperative retinal fluorescein angiography.
We tested a new stroboscopic light source for intraoperative fluorescein angiography. A pulsed xenon light source and narrow-band interference filters are coupled to a 20-gauge endoilluminator and a 35-mm camera mounted on a surgical microscope. The system was tested with good success in a patient undergoing penetrating keratoplasty. An 18- to 22-microJ flash of 2 milliseconds' duration is achieved, which is well below the safety threshold level. This new stroboscopic light source provides a flash of sufficient light intensity to perform high-resolution, high-contrast fluorescein angiography during operations for the removal of opacified media.
Aged↗
Epidemiological studies of sunlight and cataract: the critical factor of ultraviolet exposure geometry.
Despite the large body of laboratory evidence that ultraviolet radiation (UVR) is cataractogenic, epidemiological studies of the relationship between age-related cataract and chronic UVR exposure have provided apparently conflicting results. An explanation for these conflicting results could be related to errors in dosimetry. Failure to account for the biophysical, physiological and behavioral factors, as well as ground reflectance, which determine the level of UVR exposure of the lens can lead to completely wrong assignments of lifetime exposure. It is argued that by overlooking these factors, past epidemiological studies of UVR and cataract could readily be expected to produce conflicting results.
Cataract↗
Recovery from pulsed-dye laser retinal injury.
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Adult↗
Laser reflections from surgical instruments.
The potential hazards to the eye and skin from accidental exposures caused by reflected laser beams from surgical instruments has long been of concern to operating room staff members. Reflectance values for argon neodymium:YAG and CO2 laser wave-lengths were measured from 29 reference surfaces used on surgical instruments. From these measurements, nominal hazard zones could be determined for typical reflection hazards.
Equipment Design↗
Photokeratitis from 193 nm argon-fluoride laser radiation.
The threshold for photokeratitis at 193 nm was obtained for the rabbit cornea using an ArF excimer laser. Because ablation occurs at a level below that for photokeratitis, it was necessary to expose the cornea to a lengthy series of low-energy exposures. It is concluded that the 193 nm photons have such a shallow penetration depth, being limited to the outermost epithelial cells, that classical photokeratitis occurs from the fluorescence emitted at the corneal epithelial absorption site. An intact tear film may help to protect the cornea from low-level, scattered 193 nm laser radiation.
Animals↗
Radiometry and laser safety standards.
The application of occupational limits (ELs) in the outdoor laser environment requires an understanding of the radiometric methods required to evaluate field exposures with respect to the ELs. The limiting aperture required to adequately specify the EL must always be kept in mind. Since all exposure limits are defined as a function of time, electro-optical detectors and instrumentation must have an adequate temporal response and have an absence of saturation effects. As a field-expedient method thermally sensitive paper can also be employed to estimate the output radiant exposure of pulsed lasers. For evaluating potential ocular hazards in the retinal hazard spectral region (400 to 1400 nm), one should employ a 7-mm aperture. For evaluating potential hazards to the skin and the cornea, a 1-mm limiting aperture is justified. Although the impact of the 1-mm limiting aperture is to reduce the limiting power which is considered safe--the accessible emission limit for Class 1 laser products, it nevertheless is justified for field exposure of the eye, as has been shown in recent experimental studies of corneal injury.
Accident Prevention↗
Future applications of lasers in surgery and medicine: a review.
The experimental use of lasers in surgery and medicine began only shortly after the development of the first working laser system. However, the development of practical, effective, and safe surgical lasers has been lengthy with many obstacles and delays. Today the laser is used for a wide variety of surgical operations. The fundamental limits and potential for future applications of lasers in surgery and medicine are discussed.
Forecasting↗
Intraocular lens damage from Nd:YAG laser pulses focused in the vitreous. Part II: Mode-locked lasers.
Damage can be induced within the interior of a plastic intraocular lens (IOL) by a mode-locked Nd:YAG laser when the beam's focus lies well behind the IOL. This type of damage, which has not been reported, is the result of cumulative, multiple exposures. The damage differs from that created by optical breakdown (plasma formation) within the plastic, which occurs only when the beam is focused within or near the IOL surface. This type of damage can be avoided clinically by minimizing the number of pulsed exposures along the same beam path.
Humans↗
Evaluation of retinal exposures from repetitively pulsed and scanning lasers.
Threshold damage in the macaque retina is shown to be equivalent for the argon-krypton (Ar-Kr) 647 nm and the helium-neon (He-Ne) 632.8-nm lines for exposures to continuous wave (CW) radiation from 1 to 1,000 s. This equivalence allows interpolation from experiments with 647-nm, exposures at power levels that are unavailable with the He-Ne laser. To simulate He-Ne laser scanner exposures, 40-microseconds pulses of 647-nm light transmitted through a revolving disk with holes in the periphery were used to expose the retinas of monkeys under deep anesthesia at pulse repetition frequencies (PRFs) of 100, 200, 400, and 1,600 Hz for exposure durations of 1, 10, 100, and 1,000 s. The thresholds between laser exposure at 488 nm (Ar-Kr) and between laser exposure at 647 nm (Kr) are compared to assess thermal versus photochemical effects on the retina. The threshold for 488-nm pulses was consistently lower than that for 647-nm pulses at all PRFs and exposure times. The difference in thresholds increased with exposure time and PRF. The sharp decreases in 488-nm thresholds at 100-s exposure times for each PRF can be interpreted as a basically photochemical effect. The radiant exposure required for damage at 647 nm was several orders of magnitude above the radiant exposure from typical He-Ne scanner applications. From the similarity of the macaque retina to the human retina, it is concluded that no realistic ocular hazard exists from exposure to scanning laser systems of 1 mW or less, operating at higher than 100 Hz.
Animals↗
Ocular injury due to light toxicity.
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Environmental Exposure↗
Nonionizing radiation protection. Optical radiation, with particular reference to lasers.
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Eye↗
Potential laser hazards to the clinician during photocoagulation.
We measured reflected laser beams from seven different contact lenses used during laser photocoagulation to evaluate the potential hazards to the eyes of the clinician and bystanders. We found that although collimated beam reflections from the aiming beam of an argon laser photocoagulator could produce disability glare and discomfort to the laser operator (or to an individual viewing through the auxiliary eyepiece), the levels are not hazardous, by current occupational safety limits. Reflected laser light may exceed occupational exposure limits for momentary viewing by bystanders if they are within 1 meter of the laser contact lens.
Equipment Safety↗
Estimating the solar ultraviolet radiation exposure to an intraocular lens implant.
A study of the stability of ultraviolet radiation (UVR) absorbers in intraocular lenses (IOLs) upon exposure to UVR is necessary to determine efficacy. Ultraviolet stability is conventionally tested by placing the UV-absorbing IOLs in a solar simulator exposure chamber to determine any degradation of the absorber. To interpret any change requires a method of correlating the UVR exposure rate in the test chamber with the UVR exposure of the IOL in vivo. A method is derived that permits a determination of the upper limit of daily UVR exposure of the in-vivo IOL (or, for that matter, the crystalline lens) based upon knowledge of the ambient outdoor UVR exposure to the head and the threshold for photokeratitis.
Humans↗
Measured statistics of laser beam scintillation in strong refractive turbulence relevant to eye safety.
The time series of irradiance from a diverged He-Ne laser were measured using receiver aperture sizes that simulate the day-adapted and night-adapted human pupil. The data are within the saturation-of-scintillation regime wherein the irradiance variance decreases with further increases of propagation distance and refractive turbulence strength. Irradiance probability distributions, as well as the joint statistics of irradiance and duration of large irradiance values, are presented. The ocular hazard contributed by scintillation is found to decrease with increases of range and/or refractive turbulence strength; this effect is independent of the decrease of mean irradiance associated with such increases of range and refractive turbulence strength.
Eye↗
Optical hazard evaluation of dental curing lights.
The potential ocular hazards associated with the use of dental curing lights were evaluated. Recommendations are provided for precluding exposure of personnel to hazardous levels of optical radiation. Users should not stare directly into the dental curing lights at distances shorter than 25 cm (which would not be a likely event). Eye protectors which filter wavelengths below 500 nm may be desired by individual users to reduce discomfort or if surface lamination is applied.
Dental Restoration, Permanent↗