The second cranial nerve. It contains the axons of the ganglion cells of the retina ( about one million axons). Optic nerve considered as part of the central nervous system and has no neurolemma and no ability to regenerate after damage due to trauma or inflammation.
Optic nerve has 4 parts:
Optic nerve head; anterior 1mm including intraocular part.
Intra-orbital 3 cm,
Intra-canlicular 0.6 cm
Blood supplies of the optic nerve head is mainly by short posterior ciliary arteries, while blood supplies of the rest of the optic nerve is mainly by ophthalmic artery .
Optic disc; the anterior end of the optic nerve. It is 1.5 mm in diameter and lies 3 mm nasal to the post pole of the eye. At the margin of the optic disc, the choroid and all the retinal layers stop except axons of the ganglion cells of the retina which pass through the lamina cribrosa of the sclera and emerge from the eye ball as the optic nerve. Optic cup is a central depression in the disc that dose not contain nerve fibers.
Optic nerve pass through optic canal to the middle cranial fossa, where it lies over the cavernous sinus. It converges with the optic nerve of the opposite side to form the optic chiasma where nasal fibers decussate to the opposite optic tract.
Optic Nerve Disorders
Optic Neuritis: optic nerve inflammation
1-Demyelinating (MS): most common cause (70%), typically affects young adults, and women are affected more than men
Secondary optic atrophy; secondary to optic nerve head disease,
Anterior ischemic optic neuropathy
Pale, white and slightly elevated disc
Poorly delineated margins
Attenuated blood vessels
Anterior ischemic optic neuropathy Infarction of the optic nerve head caused by occlusion of the short posterior ciliary arteries
Arteritic associated with Giant cell arteritis
Non- Arteritic; idiopathic, usually occurs in hypertensive patients between 40-60 years old.
Sudden monocular visual loss
Disc appears, pale and edematous
Pupil; is the central aperture in the iris. Pupillary constriction (Miosis) is achieved by sphincter pupillae muscle, while dilatation of the pupil (Mydriasis) is achieved by dilator pupillae muscle.
A- Constriction of the pupil
Induced by Para-sympathetic innervations to the sphincter pupillae muscle of the iris
Light reflex; Constriction of the pupil when light is projected toward the eye.
Direct Light reflex; Constriction of the ipsilateral pupil