Intra-beam viewing of the direct beam and the specularly reflected beam are most hazardous when the secondary reflector is a flat and polished surface. Secondary reflections from rough uneven surfaces produce more diffuse reflections and are usually less hazardous. Extended source viewing of normally diffuse reflections are not normally hazardous except for very high power lasers (Class 4 lasers). Extra care should be taken with IR lasers since diffuse reflectors in the visible spectrum may reflect IR radiation differently and produce greater exposures than anticipated.
Fig. 1 Anatomy of the Human Eye
Laser radiation of differing wavelengths affects different portions of the eye. Refer to the diagram above as reference for the information below:
Far and Middle Infrared – (25,000 nm – 2500 nm) – Far infrared radiation is thermal in nature and is absorbed by the cornea. This may cause burns and loss of vision. Eye injury from middle infrared laser radiation is usually the result from heating or thermo-mechanical effects. This wavelength range penetrates deep into the lens and can cause cataracts
Near Infrared (2500 nm – 750 nm) and Visible (750 nm -400 nm) – This range of laser radiation can cause a retinal burn which could result in a permanent blind spot or even total blindness of the optic nerve is injured. These injuries can be painless, and the damage is permanent.
Ultra-Violet – There are two bands of ultra-violet laser radiation with respect to potential energy.
(400 nm – 315 nm) – Absorbed by the lens and may cause cataracts
(315 nm – 100 nm) – Absorbed by the cornea and may cause photokeratitis. This can be extremely
painful and result in temporary vision loss.
Symptoms of Laser Eye Injuries –
Visible Beam Lasers - Exposure can be detected by a color flash and an after-image of its complementary color. For example, a green 532 nm laser light would produce a green flash followed by a red after-image. When the retina is affected, there may be difficulty in detecting blue or green colors because of cone damage.
CO2 (Invisible) Beam Lasers - Exposure causes a burning pain of the cornea or sclera.
Laser Generated Airborne Contaminants (LGAC)
Air contaminants associated with the use of Class 3B and Class 4 lasers. In a medical setting, LGACs result from the interaction of the laser beam with tissue and can contain smoke, chemical vapors, and aerosols containing biological contaminants. Local and area ventilation must be adequate to keep airborne contaminant levels below worker exposure limits. Refer to UIHC policy on controlling exposure to laser plume for more information.
Note: The use of surgical masks alone does not provide adequate protection against exposure to LGACs.
Other Non-Beam Hazards
Certain types of lasers can produce non-beam hazards such as electrical shock, hazardous chemical exposure, and collateral radiation. For a description of these hazards, please refer to Appendix 1.
Risk of skin injury can be significant when working with high power infrared lasers or lasers which emit in the ultraviolet spectral region. Risks from infrared lasers include thermal burns and blistering or charring of the skin. Risks from UV lasers include sunburn, skin cancer, skin aging and photosensitization.