Resilience of the Fetal Eye Following Radiation Insult

Abstract

Summary and Conclusions

1) The 13.5 day fetus can sustain an exposure of 300 r and come to term. Its eyes, however, by 4 hours show massive damage to the presumptive retina such that approximately half of the cells are pycnotic or have fragmented nuclei. Many of these dead cells are sloughed off into the vitreous body or into the space between the retina and the pigmented layer. Both the inner and outer nuclear zones are involved, only the region of the ora serrata being rather free of damage. 2) At 24 hours there is evidence of continued necrosis, with about as many dead cells and nuclei as at 4 hours in spite of active phagocytosis. This suggests disintegration of some neurectoderm as it differentiates into neuroblasts. The outer neurectoderm of the presumptive retina appears to have begun proliferation. The vitreous body is rather free of dead cells and debris. 3) By 12 hours after exposure most fetal eyes have been able to repair the radiation damage and reconstitute the retina so that it appears quite normal. The eye as a whole is slightly smaller than that of the control, but the general morphology of the eye is normal. However, a few fetal eyes exhibit residual damage in the form of relatively cell-free areas and regions where the neuroblasts have been retarded in their proliferation and differentiation so as to cause the formation of rosettes. Since these were not seen at birth (6-7 days after exposure) it is presumed that they are temporary and that the retina adjusted to them. 4) Measured by the immediate (4 hr) effect, the fetal eye is very radiosensitive. However, the fetal eye exhibits remarkable reparative powers following severe radiation insult. This is achieved, not by recovery of radiation-damaged cells, but by proliferation from the more radioresistant precursor neurectoderm cells.