Fifty years ago: ‘Laser hazards’

John Rich

Medical Officer C. A. Parsons & Co. Ltd.

In 1958 A. L. Shawlow and C. H. Townes postulated the laser. T. H. Maiman succeeded in obtaining laser action in 1960. Before long, lasers are expected to appear in most laboratories and many factories, so it is an opportune time to examine their hazards.

So far lasers have been devised to operate in about 15 frequencies of visible light and in ultra-violet and infra-red modes. It is not surprising that the laser has stimulated an enormous amount of scientific interest with the challenging possibilities of its properties. So many uses were originally proposed that it was dubbed ‘a solution in search of a problem’.For the purposes of this paper it will be sufficient to note that uses have been suggested in communications, navigation, cutting and welding, machine alignment, surveying, measurement, rangefinding, photography, military, optical, physical, chemical, biological and medical applications. It is probable that all laser beam properties have significance in biology and medicine. Its optical properties make it easy to direct a small beam at portions of tissue down to microscopic size. When it is focused and its energy is concentrated into a small area, its destructive power may be selectively let loose on structures which absorb light at the wavelength used. Micro-dissection may thus be achieved and there are surgical possibilities.

Though the skin acts as a light barrier, the eye forms not only a transparent window for deeper structures but also a focusing device. Solon, Aronson and Gould (1961) early drew attention to the eye hazards and gave formulae for calculating retinal energy density from a laser beam. They showed that the pulse from a small ruby laser gave a density at least six times that known to cause solar retinal burns, and considered this might be utilized in ophthalmology.

It is known that 6943 A light is practically unabsorbed in the eye until it reaches the retina. It is also of low visual luminosity, and this, with the short duration of the pulse (0-0008sec), makes it scarcely perceived by the patient. So it is possible that an accidental exposure in a laser operator would not be perceived by the victim. Thus, though the laser may be used very successfully for retinal surgery, the laser beam presents a definite hazard to the eye, which, if minimal, can easily be insidious. For this reason it is advisable for laser users, especially in research work, to undergo regular ophthalmic examinations. There should be a pre-employment examination to obtain a norm. Probably only one-eyed or virtually one-eyed workers should be excluded from laser work. Further examinations should be at regular intervals, say six months as an arbitrary period, or whenever an operator believes he has had a beam exposure or develops eye symptoms. Each examination should include visual acuity, visual fields, ophthalmoscopy and slit lamp examination. They will have the three-fold effect of detecting retinal lesions, lesions in other eye structures, such as corneal cataract from unrecognized infra-red lasing, and checking on lax or insufficient safety precautions.

It has been suggested in an occasional survey in the Lancet (1964) that the definition of the biological effects of the laser beam raises a problem as great as that originally presented by the discovery of ionizing radiation. Certainly the biological effects of laser light are largely unknown at present, especially in the long term.

From: Laser hazards. Trans Ass Industr Med Offrs (1965) 15, 147. Available at: Occup Med (Lond) 1965;15:147–149. doi:10.1093/occmed/15.1.147.

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