What is the optic nerve?

The optic nerve is comprised of millions of nerve fibers that send visual messages to your brain to help you see. You have an optic nerve at the back of each eye that connects directly to your brain.

What is the purpose of the optic nerve?

The optic nerve is critical to your vision. It’s an extension of your central nervous system, which includes your brain and spine.

The optic nerve transmits electrical impulses from your eyes to your brain. Your brain processes this sensory information so that you can see.

Where is the optic nerve?

The optic nerve is the second of 12 cranial nerves. Each eye has its own optic nerve.

The optic nerve:

• Starts in the optic disk, a group of cells in retinal tissue at the back of your eye.
• Travels through the optic canal (a bony opening) and enters your skull.
• Crosses paths with the opposite optic nerve to form an X-shaped structure called the optic chiasm.
• Creates upper and lower pathways called the optic radiations (ORs).

The OR pathways carry nerve messages to a part of your brain called the visual cortex. The visual cortex processes sensory information for sight.

What are the optic nerve branches?

Each optic nerve has branches that travel to your brain or join with other fibers. When the two optic nerves cross at the optic chiasm:

• Half of the nerve fibers from your left eye continue to the left side of your brain.
• Half of your right eye’s nerve fibers connect to the right side of your brain.
• The remaining nerve fibers join together. Your brain receives signals from both eyes at the same time to create a cohesive visual image (binocular vision).

What conditions and disorders affect the optic nerves?

These conditions can damage an optic nerve and affect vision:

• Glaucoma: Fluid buildup in the front part of your eye puts pressure on the optic nerve. The pressure damages your optic nerve. Glaucoma is the leading cause of blindness in adults over 60.
• Anterior ischemic optic neuropathy: Loss of blood flow to the optic nerve causes anterior ischemic optic neuropathy. The condition causes sudden vision loss.
• Congenital abnormalities: Sometimes babies are born with differences in their optic nerve(s) that may lead to poor vision.
• Optic atrophy: Lack of blood to the optic nerve causes it to shrink. Potential causes of optic atrophy include trauma, strokes, hydrocephalus, infections and brain tumors. Some cases are inherited.
• Optic nerve coloboma: This inherited condition causes one or both optic nerves to not develop as they should.
• Optic nerve drusen: This condition occurs when protein and calcium deposits (drusen) build up on the optic nerve.
• Optic nerve gliomas: Gliomas are tumors (growths) on the optic nerve. They’re usually benign (not cancerous). These tumors often affect people who have an inherited condition called neurofibromatosis type 1 (NF1).
• Optic nerve meningiomas: These slow-growing tumors are rare and benign, but can lead to severe vision loss.
• Optic neuritis: Infections and autoimmune diseases like multiple sclerosis can irritate or inflame the optic nerve, causing optic neuritis.
• Papilledema: Pressure around your brain from a traumatic brain injury, brain tumors, meningitis or another problem causes the optic nerve to swell.
• Neuromyelitis optica (NMO): Also called Devic's disease, NMO occurs when the immune system mistakenly attacks the optic nerves and spinal cord.

What are the signs of optic nerve disorders?

Optic nerve problems cause various symptoms depending on the underlying condition. The symptoms may be temporary or permanent. You may experience:

• Color blindness.
• Eye pain.
• Headaches.
• Nausea and vomiting.
• Night blindness.
• Partial or complete vision loss.
• Peripheral (side) vision loss.
• Ringing in your ears (tinnitus).

How can I protect my optic nerves?

These steps can help protect your vision:

• Get regular eye exams.
• Maintain a healthy weight through exercise and a nutritious diet.
• Manage conditions that affect vision and nerves, such as diabetes and high blood pressure.
• Seek help to quit smoking. Smoking increases the risk of optic nerve damage and other vision problems.
• Wear sunglasses and eye protection (goggles or safety glasses) when engaged in sports or activities that could affect your eyes.

When should I talk to a doctor?

You should call your healthcare provider if you experience:

• Changes to your eyesight, including blurred or double vision or vision loss.
• Chronic headaches.
• Eye pain.

A note from Cleveland Clinic

Your optic nerves are vital to your eyesight. Damage to these nerves can lead to temporary or permanent vision loss. Glaucoma is the most common optic nerve disorder. If left untreated, optic nerve damage can lead to blindness. Regular eye exams are essential to protect your sight and stop optic nerve damage before it gets too severe.