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 produce ocular anomalies on gestational day 9. A study was performed to determine whether ocular anomalies are induced in rat F1 offspring at this dose level on gestational days 6, 7, 8, 9, 10, and 11. Eyes were examined during postnatal week 5 using indirect ophthalmoscopy and biomicroscopy. 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, respectively. There were no treatment-related ophthalmological abnormalities at the other time points. It is concluded that the most sensitive period for induction of ocular anomalies by soft x-ray irradiation at a dose of 4.6 Gy under these experimental conditions is during gestational days 8 and 9, and that gestational day 9 appears to be more sensitive than day 8.