Cataracts occur frequently among workers who deal with hot material such as molten glass or steel, as a result of exposure to intense infra-red radiation (IR) emitted from it. To investigate this hazard, a theoretical model of the human eye being exposed to IR was developed, and the temperature distributions within it were calculated. It is suggested that IR cataracts in the workplace result from the generation of heat by absorption of IR in the cornea and heat conduction to the lens. The threshold IR irradiances for cataract formation were determined from the relationship between the incident irradiance and the lens temperature, and were in the range 163-178 mWcm-2 for long-term exposures (greater than about 5 min) under normal conditions. However, these values may be reduced by 50% for workers who perform heavy work at a high ambient temperature. It may be possible to set IR exposure limits in the workplace based on these threshold data.
