Document 6warJKGqmnD06qD2ZNM4eRO3g

FlC 44-26 --Observing laser light Above Par allel ravs of a laser may be focused to a point image bv the eve Below Rays from an extended source (as from a conventional lamp, or rays from a diffuse reflection of a laser beam) produce a sizeable (and less dangerous) image at the retina tion of a laser beam) produce a sizeable image at the retina Light from a laser entenng the eye is concentrated 100,000times at the retina Because of this focusing effect, the eye is by far the organ of the body most subject to dam age Hence, injury to the skin is seldom of concern except in dealing with very highpowered lasers Exposure criteria. A number of groups0 and others have developed recommended safe ocular exposure levels for laser radia tion (subsequently referred to as safe levels) Since the threshold doses presented in most biologic research literature are generally presented in terms of retinal intensities, early standards proposed safe levels at the retina Such levels created serious problems for many users who were not familiar enough with physiological optics to extrapolate reti nal doses to the exterior (cornea) of the eye Safety factors ranging from two to 100 have been utilized by different groups in arriving at safe levels from the same biologic data Opinion vanes as to whether safety levels should be based upon cell damage detected by biomicroscopic methods, by clearly evi dent damage to the retina determined ophthalmoscopically, or by detectable functional loss of vision It may well be that there ex ists a significant difference between acute and chronic effects of laser exposure In gen eral, it has been the practice on the part of those who have proposed safe levels to be conservative Except where lasers are uti lized m an outdoor environment over long ranges, conservative levels have not resulted tn significant operational restrictions Safe levels which have been utilized by the U S Army Environmental Hygiene Agency are (joules per square centimeter--a unit for predicting damage potential of a laser beam) I0"7 j/sq cm for q-switched and 10~* j/sq cm for non-q-switched pulsed lasers based upon a wavelength of 694 3 mpt, and 10-6 W/sq cm for continuous-wave lasers, based upon white light Additional safety factors of from two to ten are utilized with these levels, depending upon the situation Reflections. The foregoing exposure crite ria assume that the incident laser radiation consists of a parallel beam and that the eye is focused at infinity This would be true for intra-beam viewing within the direct beam or for a specularly reflected beam, however, most reflections which individuals view are diffuse in nature A safe retinal irradiance The Amencan Conference of Governmental Industnal Hygienists A Guide for Uniform Indus trial Hygiene Codes or Regulations for Laser In stallations, Cincinnati, March 1968 The Electronic Engineering Association A Gen eral Guide to the Safe Use ofLasers, London, Sep tember 1966 Sperling, H G , editor Laser Eye Effects, a report of the Armed Forces NRC Committee on Vision, Washington, D C, April 1968 U S Atomic Energy Commission, Nevada Opera tions Office Recommendations of the Ad Hoc Laser Committee, Standards for Laser Safety, USAEC Nevada Operations Office, I as Vegas, October 1967 Weston, B A Laser Systems--Code of Practice, London, The Ministry of Aviation, November 1965 1499