CRITICAL PERIOD FOR INDUCTION OF OCULAR ANOMALIES PRODUCED BY SOFT-X-RAY IRRADIATION (4.6 GY) IN THE RAT F1 OFFSPRING

A minimal dose of soft x-ray irradiation of 4.6 Gy is expected to prod uce ocular anomalies on gestational day 9. A study was performed to de termine whether ocular anomalies are induced in rat F-1 offspring at t his dose level on gestational days 6, 7, 8, 9, 10, and 11. Eyes were e xamined during postnatal week 5 using indirect ophthalmoscopy and biom icroscopy. Anophthalmia (1.3% and 12.1%), microphthalmia (3.8% and 6.9 %), iris coloboma (3.8% and 6.9%) and choroidal coloboma (2.5% and 8. 6%) were observed in the gestational day 8 and 9 treatment groups, res pectively. There were no treament-related ophthalmological abnormaliti es at the other time points. It is concluded that the most sensitive p eriod for induction of ocular anomalies by soft x-ray irradiation at a dose of 4.6 Gy under these experimental conditions is during gestatio nal days 8 and 9, and that gestational day 9 appears to be more sensit ive than day 8.