what is optic nerve

It develops in the framework of optic stalk as
below:

• The neuroectodermal cells forming the walls of optic stalk develop into glial system of the nerve.
• Fibres from the nerve fibre layer of retina grow into optic stalk by passing through the choroidal fissure and form the optic nerve fibres.
• The fibrous septa of the optic nerve are developed from the vascular layer of mesenchyme which invades the nerve at 3rd fetal month.
• Sheaths of optic nerve are formed from the layers of mesenchyme like meninges of other parts of central nervous system.
• Myelination of nerve fibres takes place from brain distally and reaches the lamina cribrosa just before birth and stops there. In some cases, this extends up to around the optic disc and presentsas congenital opaque nerve fibres. These develop after birth.