The optic vesicles project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk.
Closure of the choroidal fissure in the optic stalk occurs during the seventh week of development. The former optic stalk is then called the optic nerve.Kaplan Qbook - USMLE Step 1 - 5th edition - page 55 In short, the optic stalks are the structures that precede the optic nerves embryologically.
References
External links
Overview at vision.ca