A cataract is a clouding of the normally clear lens of the eye.
A much higher incidence of cataracts was reported among physicists in cyclotron
laboratories whose eyes had been exposed intermittently for long
periods of time to relatively low radiation fields, as well as among atomic
bomb survivors whose eyes had been exposed to a single high radiation
dose. This shows that both chronic and acute overexposure of the eyes
can lead to cataracts. Radiation may injure the cornea, conjunctiva,
iris, and the lens of the eye. In the case of the lens, the principal
site of damage is the proliferating cells of the anterior epithelium.
This results in abnormal lens fibers, which eventually disintegrate
to form an opaque area, or cataract, that prevents light from
reaching the retina.
The cataractogenic dose to the lens is on
the order of 500 rad of beta or gamma radiation. No radiogenic
cataracts resulting from occupational exposure to x-rays have
been reported. From patients who suffered irradiation of the eye
in the course of x-ray therapy and developed cataracts as a consequence,
the cataractogenic threshold is estimated at about 200 rad. In
cases either of occupationally or therapeutically induced radiation
cataracts, a long latent period, on the order of several years,
usually elapsed between the exposure and the appearance of the lens
opacity. The cataractogenic dose has been found, in laboratory
experiments with animals, to be a function of age; young animals
are more sensitive than old animals.