\ Ann. occup Hye , Vol 35, No. 1, pp. 1-12, 1991 Pnnted in Grt»t Briuui
0003^878/91 S3D0+0.00 Petyamon Prca pic © 1991 British Occupational Hygiene Society.
THERMAL EFFECT OF INFRA-RED RADIATION ON THE EYE: A STUDY BASED ON A MODEL TSUTOMU OKUNO
National Institute of Industrial Health, 21-1, Nagao 6 chome, Tama-ku, Kawasaki 214, Japan (Received 7 August 1990 and in final form 6 September 1990)
INTRODUCTION
IT HAS been suggested since the nineteenth century that there was an increased incidence of cataract among workers who had dealt with molten glass or steel for many years. At the beginning of the twentieth century, it was already recognized that these cataracts were produced by infra-red radiation (i.r.) emitted from such hot material. Since then a number of epidemiological and experimental investigations of this type of cataract (i.r. cataract) have been conducted, but the mechanism involved or the amount of i.r. required for cataract formation is still unknown because of the lack of quantitative data. There are two possible types of i.r. effect on the eye, photochemical and thermal, but it is uncertain which leads to cataract formation. In general the photochemical effect of i.r. is very weak, because its photon energy is low compared with molecular electronic energy. It is therefore reasonable to assume that i.r. cataracts result from the thermal effect, that is, from the rise in temperature of the lens of the eye induced by exposure to i.r. In fact, animal experiments showed that increases in temperature of the lens of several degrees resulted in cataract formation (EMERY et al., 1975; KRAMAR et al., 1987). However, in order to confirm this it must be shown that the temperature rises of the human lens induced by i.r. levels in the workplace are sufficient to develop cataracts. If the assumption is correct, the temperature rise of the lens is considered to represent the i.r. hazard quantitatively, and can be used for its evaluation. By investigating this, for example,, it is possible to determine the threshold i.r. irradiance for cataract formation. However, it is impossible to measure human lens temperatures directly, and it is also quite difficult to estimate them from results of animal experiments. The only possible method may be to develop a theoretical model of the human eye and to calculate temperatures within it. This method is particularly effective in this case, because heat transport within the eye occurs mostly by conduction that can be
Downloaded from http://annhyg.oxfordjournals.org/ at Russian Archive on December 11, 2013
Abstract—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.
2
T. OKUNO
MODEL
In the model black-body radiation of temperature 1200°C (the working temperature of glass) or 1500°C (the melting point of iron) is incident on the eye. Its spectral distribution is given by Planck's equation. As is seen from Table 1, this
TABLE 1. THE ENERGY DISTRIBUTION OF THE INCIDENT BLACK-BODY RADIATION AMONG THE SPECTRAL REGIONS
Spectral region Temperature of radiation 1200 1500
Ultraviolet
Visible
i.r.-A
Infra-red i.r.-B
i.r.-C
0003^878/91 S3D0+0.00 Petyamon Prca pic © 1991 British Occupational Hygiene Society.
THERMAL EFFECT OF INFRA-RED RADIATION ON THE EYE: A STUDY BASED ON A MODEL TSUTOMU OKUNO
National Institute of Industrial Health, 21-1, Nagao 6 chome, Tama-ku, Kawasaki 214, Japan (Received 7 August 1990 and in final form 6 September 1990)
INTRODUCTION
IT HAS been suggested since the nineteenth century that there was an increased incidence of cataract among workers who had dealt with molten glass or steel for many years. At the beginning of the twentieth century, it was already recognized that these cataracts were produced by infra-red radiation (i.r.) emitted from such hot material. Since then a number of epidemiological and experimental investigations of this type of cataract (i.r. cataract) have been conducted, but the mechanism involved or the amount of i.r. required for cataract formation is still unknown because of the lack of quantitative data. There are two possible types of i.r. effect on the eye, photochemical and thermal, but it is uncertain which leads to cataract formation. In general the photochemical effect of i.r. is very weak, because its photon energy is low compared with molecular electronic energy. It is therefore reasonable to assume that i.r. cataracts result from the thermal effect, that is, from the rise in temperature of the lens of the eye induced by exposure to i.r. In fact, animal experiments showed that increases in temperature of the lens of several degrees resulted in cataract formation (EMERY et al., 1975; KRAMAR et al., 1987). However, in order to confirm this it must be shown that the temperature rises of the human lens induced by i.r. levels in the workplace are sufficient to develop cataracts. If the assumption is correct, the temperature rise of the lens is considered to represent the i.r. hazard quantitatively, and can be used for its evaluation. By investigating this, for example,, it is possible to determine the threshold i.r. irradiance for cataract formation. However, it is impossible to measure human lens temperatures directly, and it is also quite difficult to estimate them from results of animal experiments. The only possible method may be to develop a theoretical model of the human eye and to calculate temperatures within it. This method is particularly effective in this case, because heat transport within the eye occurs mostly by conduction that can be
Downloaded from http://annhyg.oxfordjournals.org/ at Russian Archive on December 11, 2013
Abstract—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.
2
T. OKUNO
MODEL
In the model black-body radiation of temperature 1200°C (the working temperature of glass) or 1500°C (the melting point of iron) is incident on the eye. Its spectral distribution is given by Planck's equation. As is seen from Table 1, this
TABLE 1. THE ENERGY DISTRIBUTION OF THE INCIDENT BLACK-BODY RADIATION AMONG THE SPECTRAL REGIONS
Spectral region Temperature of radiation 1200 1500
Ultraviolet
Visible
i.r.-A
Infra-red i.r.-B
i.r.-C
