Laser eye injuries.

Methodology for the evaluation of potential optical radiation hazards has been developed in response to the increasing use of high radiance optical sources, such as lasers, compact arc lamps, tungsten-halogen lamps, and electronic flash lamps. Recent biological investigations of injury from ultraviolet radiation and studies of chorioretinal injury from high radiance sources permit a realistic ocular hazard evaluation. Safe exposure criteria that may be readily applied to practical situations have been developed from the available biological data and from experience with occupational hazards. Hazard evaluation techniques, hazard data, and general control measures are provided for a number of commonly encountered ultraviolet, visible, and infrared sources.

Evaluation of Optical Radiation Hazards

The authors measured temperature rises with specially designed microthermocouples in over 60 retinae for various image sizes, wavelengths, and exposure durations. Measured temperatures varied with a standard error of 6 percent, and agreed well with a mathematical model for temperature-time response. Observed injury also compared favorably to that predicted by a rate process model for thermal injury. Suggested rate constants for the eye are A = 1.3 ×1099 1/s, and E = 150 000 cal/M. With these coefficients, predicted threshold injury agreed within a factor of two with experimentally determined injury from 10?8 to 103 s. No difference in threshold temperatures was evident between either macular and paramacular exposures or between wavelengths of 488-647 nm. The model can be used to predict injury in the human eye by substituting absorption coefficients and thickness for the human PE and Ch in the thermal portion of the model.

Measurement and Prediction of Thermal Injury in the Retina of the Rhesus Monkey

During the last quarter century there has been a marked development and increased utilization of equipment and devices for military, industrial, consumer-use, entertainment, and medical applications that emit a large variety of nonionizing radiant energies. These include ultraviolet, infrared, visible light, microwaves, and radio-frequency waves, which are all classified as electromagnetic waves. Many of the electro-magnetic waves at certain frequencies, power levels, and exposure durations can produce biological effects or injury depending on multiple physical and biological variables. Although equipment which utilizes or emits electromagnetic waves provides immeasurable benefits to mankind, it may also create potential hazards to the individual through uncontrolled and excessive radiation emissions. Consequently, questions are being raised such as: 1) How serious are these problems, what are their dimensions, and what acute and/or chronic effects on the human body may be involved? 2) How adequate is our present knowledge about personnel hazards of these radiation types? 3) How can exposure be reduced? 4) How can better regulation be obtained to reduce exposure? This paper reviews the pathophysiology of exposure to ultraviolet, infrared, coherent electromagnetic radiation (laser), microwaves, and radio-frequency radiation, and the protection guides which have been established for these energies. It is also pointed out that there is a need to set limits on the amount of exposure individuals can accept with safety; setting standards, however, is a very complicated process. The objectives of protection are to prevent acute effects and to limit the risks of late effects. The second objective, namely, to limit the risk of possible late effects, becomes difficult. Protection standards are the results of empirical approaches to various problems reflecting current qualitative and quantitative knowledge. A numerical value for a standard of effect implies a knowledge of the effect produced at a given level of stress, and that both effect and stress are measurable. One problem is the definition of what an "effect" is and whether it can ultimately be shown to modify man's "way of life" or that of his offspring. If there were a clear-cut relationship between exposure level and pathophysiologic effect, the problem of setting standards would be greatly simplified. Not only are there numerous variables to be considered, but it is often difficult or impossible to obtain the necessary data to draw valid conclusions concerning effects of exposure to various radiant energies. It is important to maintain a proper perspective, and assess realistically the biomedical effects of these radiant energies so that the worker or general public will not be unduly exposed nor will research, development, and beneficial utilization of these energies be hampered or restricted by an undue concern for effects which may be nonexistent or minimal in comparison to other environmental hazards. There is a need for scientific competence--research aimed at creating credible knowledge and data which can stand against the pressure of legal challenge as well as the understandable bias of special interest groups.

Human exposure to nonionizing radiant energy&#8212;Potential hazards and safety standards

Retinal-temperature increases produced by circularly symmetric exposures to electromagnetic radiation between 400 and 1200 nm were calculated for a wide range of image sizes. Temporal, axial, and radial temperature distributions are described. Constant and exponentially decreasing source strengths are considered. Solutions of the heat-conduction equation are expressed in terms of both retinal irradiance and the total power entering the eye. Application of solutions to the prediction of thresholds for retinal damage is discussed, and excellent agreement is noted between theoretical predictions and experimental observations of the spectral dependence of chorioretinal damage thresholds.

Spectral dependence of retinal damage produced by intense light sources.

The eyes of rhesus monkeys and humans were exposed to long-pulsed ruby and neodymium, Q-switched ruby and neodymium, and helium-neon (He-Ne) lasers to determine retinal damage thresholds. Rabbit ey...

Thresholds of laser eye hazards.

A Q-switched ruby laser was used to produce retinal lesions in rabbits and monkeys. The data were obtained with special attention given to eliminating inhomogeneities from the portion of the laser beam entering the eye; correcting each eye for refractive error to produce minimal retinal impact area; estimating the retinal area impacted; monitoring of the laser output in space, time, and amplitude; and to detailed clinical and pathological observations. Eight microjoules in pigmented rabbits and 22μj in rhesus monkeys for 8-nano-second pulses gave a 50% probability of producing a clinically observable lesion. Histologically, lesions were seen at approximately half this level. Energy density or power density at the retina is the determining factor for threshold damage. Histologically, glial reaction was conspicuously deficient. However, two instances of local pigmentcell hyperplasia were observed.

https://jamanetwork.com/journals/OPHTH/articlepdf/628978/archopht_78_5_015.pdf

Experimental q-switched ruby laser retinal damage.

: Results of experimental investigations to determine threshold levels for minimally-sized retinal lesions caused by neodymium long-pulsed and Q-switched lasers are presented. The experimental animals were rhesus monkeys. In addition, results of retinal damage due to Q-switched ruby, neodymium, and doubled neodymium lasers at suprathreshold energy levels are also presented. A report on histopathology of retinal injury caused by Q-switched lasers is presented. Observations on damage due to both ruby and neodymium lasers are discussed. The design and construction of a fundus reflectometer is described, and preliminary measurements of fundus reflectance of rabbit, rhesus monkey, and human subjects are reported. Results of an experimental investigation to determine threshold damage levels for a CO2 laser to rabbit corneas are given. Data for three exposure times are included. In addition, theoretical calculations based on a one-dimensional heat-flow model are reported, and comparison is made with the experimental results. Finally, some results on permanent corneal damage due to CO2 laser are reported. (Author)

R. C. Honey

Papers

Thresholds of laser eye hazards.

Experimental q-switched ruby laser retinal damage.

Investigations of laser damage to ocular tissues.

Thresholds of laser eye hazards.