Histological examination of chick embryos with bilateral microphthalmus with reference to laterality in the visual...

The histological abnormalities of chick embryos with bilateral microphthalmus were examined in serial paraffin sections with special reference to laterality in the visual apparatuses, including the cornea, lens, neural retina and pigment epithelium. There was marked laterality in the above structures; some eyeballs had individual, if incomplete, sublayers of the cornea and the neural retina, and others not. The sublayers of the neural retina were occasionally observed even in eyeballs at the stage of optic vesicle formation, in contrast to the previous notion that the pigment epithelium induces the maturation of the primordial neural retina after optic vesicle differentiation into the optic cup. There was also a case where developmental differences between the right and left eyeballs were absent except in the lens. These findings suggest that chick embryos with bilateral microphthalmus exhibit a more complex histological profile or diversity than previously considered, possibly as a result of the differential actions of various mutagens and endogenous trophic factors on the developing visual system.