The effect of diagnostic-quality X-irradiation on the developing postnatal rat retina

Abstract

The morphological effect of diagnostic-quality X-rays (140 kVp, 2·35 mm Al h.v.l.) on the developing postnatal rat retina was studied by the use of light and electron microscopy. Different litters of postnatal rats were exposed to 100 röntgens (R) of X-rays on each of the first seven days of life (day 0 through day 6, day 0 being the day of birth). Examination with light and electron microscopy on day 8 and day 14 revealed that the postnatal retina was insensitive to the induction of permanent retinal injury at the 100 R exposure level. No visible abnormalities that could be attributed to the effect of the irradiation were demonstrated in any of the retinal layers. Animals exposed on postnatal day 3 or day 4 to 200, 300, or 500 R of diagnostic-quality X-rays demonstrated severe injury within the outer layers of the sensory retina. The types of developmental lesions observed included (1) generalized dysplasia of the outer nuclear layer, (2) clusters of aberrant receptor cells within the photoreceptic inner and outer segments, (3) foci of apparent agenesis of the inner and outer segments and of the outer plexiform layer, and (4) the presence of an extra fiber layer within the inner nuclear layer. It was concluded that a threshold exposure exists for diagnostic-quality X-rays which is between 100 and 200 R, and that the rat retina is considerably more radiosensitive on postnatal day 3 than on postnatal day 4.