Critical Period for Induction of Ocular Anomalies Produced by Soft X-Ray Irradiation (4.6 Gy) in the Rat F₁ Offspring

Abstract

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 treament-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.