Electroretinography in the diagnosis of thallium intoxication

Abstract

Appearance of dystrophic alterations in the retina was carried out by administering 0.2 ml 12 mM of tallium chloride solution into the vitreous humour of 9 rabbits. Electroretinographic examination revealed a decline in the b wave either decreasing 2-3 times or entirely disappearing as early as on day 2 after the administration of tallium chloride. Electron microscopic investigation suggested that photoreceptors of the retina were initial by involved in the pathological process. Namely, the external segments of the photoreceptors were found to be reduced, indicating impairment of the formation of photoreceptor disks, which is known to proceed continuously under normal conditions. In the absence of an electroretinogram (ERG), the photoreceptor layers were shown to have disappeared completely. An examination of 28 subjects who were exposed to tallium and its compound at work revealed impaired retinal electrogenesis, as evident from subnormal ERG responses. This was of a functional nature and became more pronounced as occupational exposure time increased. The fact that the internal retinal layers and the 3-rd neurone remained intact, as suggested by the electrical sensitivity of the eye and lability of the optic nerve as well as by static perimetry, correlated with the EM findings obtained in experiments. Ophthalmobiomicroscopic examination of 12 eyes yielded data on characteristic changes in the lens when visual functions remained intact. These findings suggest that changes in the ERG may be indicative of initial preclinical symptoms of tallium intoxication and as such can be used when persons exposed to it in industry receive check-ups.