What is the outermost layer of the optic nerve sheath a continuation of?

Meningeal dura-the optic nerve comes off the base of the brain and passes through the optic canal. as it leaves the brain, it still retains all of the meningeal layer coverings. so, it is covered by meningeal dura, arachnoid membrane, and pia mater. this is significant, because an increase in intracranial pressure will increase the pressure in the subarachnoid space. this may squeeze the optic nerve and make the optic nerve bulge into the eye, a condition known as papilledema. the periosteal dura is the layer of periosteum covering the internal surface of the calvaria. the retina is the inner layer of the eyeball which receives and absorbs visual light rays.