The optic nerve is usually used clinically as the beginning of the optic pathway. The optic nerve begins at the optic disc, which is also known as the optic nerve papilla (referred to as the optic papilla). A large number of optic nerve fibers exit the eye via the scleral sieve and enter the skull via the orbit and optic canal, and the optic nerve in both eyes intersects and ends at the optic cross, with a total length of about 40 mm. Therefore, the optic nerve can be divided into four parts according to its travel: the intraocular segment (about 1 mm), the intraorbital segment (about 25-30 mm), the intracranial segment (about 4-9 mm), and the intracranial segment (about 10 mm).