Thermal effect of infra-red radiation on the eye: a study based on a model.

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 (i.r.) emitted from it. To investigate this hazard, a theoretical model of the human eye being exposed to i.r. was developed, and the temperature distributions within it were calculated. It is suggested that i.r. cataracts in the workplace result from the generation of heat by absorption of i.r. in the cornea and heat conduction to the lens. The threshold i.r. irradiances for cataract formation were determined from the relationship between the incident irradiance and the lens temperature, and were in the range 163-178 mW cm-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 i.r. exposure limits in the workplace based on these threshold data.