Formation of the Optic Placode

The formation of the optic placode is a complex embryological process that begins with the interaction between the surface ectoblast and the neural tube. At this early stage, the neuropore and the encephalic groove are not yet completely closed, allowing the appearance of the first optic primordia. This phenomenon is mainly due to lateral expansion, facilitated by cell communication mechanisms such as autocrine, paracrine, and juxtacrine interactions. Notably, the inhibition of the sonic hedgehog (HH) factor at the tip of the precordal plate plays a decisive role in this dynamic.

The formation of the primary optic vesicle follows this first step, where two lateral vesicles emerge and cause swelling of the epiblastic tissue, giving rise to the primitive optic placode. This process occurs between the seventh and eighth day of embryonic development. The transformation of the neural plate into a groove and its closure to form the neural tube are also influenced by the notochord. In parallel, the amniotic fluid surrounding the optic placode will later transform into cerebrospinal fluid (CSF). Finally, the presence of a colobomic fissure, through which the hyaloid artery passes, is essential for the development of the optic placode and associated structures.