The retinal nerve fiber layer (nerve fiber layer, stratum opticum, RNFL) is formed by the expansion of the fibers of the optic nerve; it is thickest near the porus opticus, gradually diminishing toward the ora serrata.

As the nerve fibers pass through the lamina cribrosa sclerae they lose their medullary sheaths and are continued onward through the choroid and retina as simple axis-cylinders.