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.

Ocular effects produced by experimental lasers.

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.

Ocular Effects Produced by Experimental Lasers: III. Neodymium Laser

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

R. M. Shuman

Papers

Experimental q-switched ruby laser retinal damage.