ABSTRACT
The present work was concerned with the development of the retina and optic nerve of the chick embryo and the effect of ethambutol on its development together with the explanation of the possible hazards of antituberculous drugs which May occur To the foetus, if the pregnant mother is under the treatment with these drugs. Histological studies were made on the retina and optic nerve of 9,11 and 15 days chick embryos injected on the 6 th day of incubation with a dose of ethambutol equivalent to the human therapeutic dose [0.8mg/chick embryo]. It was found that ethambutol induced retardation of growth and degenerative changes in the layers of the retina associated with reduction in the size of the optic nerve. As age advenced at 15 day of incubation, regeneration of retina started and progressed gradually till full term, but its size was still less than the control embryo of the same age