Home Patients & Public What is the optic nerve?

What is the optic nerve?

The cable that connects your eye to your brain

Reviewed by Dr. James Deom, OD, MPH, FAAO, FSLS, Chief of Eye Care Services, Hazleton Eye Specialists Last reviewed: November 12, 2026 Audience: Patients & public

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Your optic nerve carries signals from the eye to the brain, where they become the pictures you see. It is made of about a million tiny nerve fibers bundled together, like the wires inside a cable. Each eye has its own optic nerve.

Where it starts

The nerve fibers begin in the retina, the light-sensing layer at the back of the eye. They gather at the optic disc (also called the optic nerve head), leave the eye through a small opening, and travel back toward the brain. The two optic nerves meet behind the eyes, at a crossing point called the chiasm.²

Labeled cross-section of the optic nerve head. Retinal nerve fibers turn at the disc and pass through the scleral canal and the mesh-like lamina cribrosa into the optic nerve, which is wrapped in dura, arachnoid and pia with fluid-filled subarachnoid space. Short posterior ciliary arteries form the circle of Zinn-Haller around the nerve. The central retinal artery and vein run in the center of the nerve. — The optic nerve head, where about a million nerve fibers leave the eye through a small opening in the sclera. Its front part (prelaminar and laminar regions) depends mainly on the short posterior ciliary arteries. Schematic, not to scale.

The optic disc has no light-sensing cells, so it creates a small blind spot in each eye. You don’t notice it, because your brain fills in the gap.

What eye doctors look at

During a dilated exam, your eye doctor can see the optic disc directly. They look at its color, its edges, and the cup, the small central dip in the disc.

Two optic discs side by side. On the left, a typical disc with a pale central cup about 0.4 times the width of the disc. On the right, a smaller disc with no visible cup, labeled a crowded disc at risk, with C/D under 0.2. — Cup-to-disc ratio compares the width of the central cup with the width of the whole disc. A small, crowded disc with little or no cup is the main known structural risk factor for NAION. It is common, and most people who have one never develop NAION. Schematic, not to scale.

OCT imaging measures the thickness of the nerve fiber layer around the disc, so changes can be tracked over time.¹ See What to expect at an eye exam.

What can affect the optic nerve

Reduced blood flow: NAION, giant cell arteritis, and PION
Eye pressure damage: glaucoma
Inflammation: optic neuritis
Raised pressure around the brain: papilledema and IIH
Deposits in the nerve: optic disc drusen
Pressure from a growth or swollen tissue: compressive optic neuropathy
Inherited conditions: LHON and DOA
Medicines, toxins, or low vitamins: toxic and nutritional optic neuropathy
Injury: traumatic optic neuropathy

Optic nerve fibers do not grow back once they are lost, so finding problems early and getting same-day care for sudden vision loss matter. See Warning signs and FAQ.

Your optic nerve and GLP-1 medicines

If you take a GLP-1 medicine such as semaglutide or tirzepatide, read GLP-1 medicines and your eyes.

Dr. Deom’s recommendation (clinical opinion / practice recommendation)

Dr. James Deom recommends that everyone starting or taking a GLP-1 medication have a comprehensive dilated eye exam with OCT, OCT angiography (OCTA), and retinal photography (fundus photos with autofluorescence) as a baseline and for follow-up, and seek same-day care for sudden vision loss.

This is his clinical opinion, not a formal rule from every professional group. AAO and NANOS do not recommend an eye exam only to predict NAION, and no test can reliably predict or prevent it. Dr. Deom recommends the baseline so there is a record to compare against if anything changes, and so other eye problems can be found early.

Dr. James Deom’s personal clinical thought

This is his opinion, not established evidence. It is not a finding from the studies or a position of the FDA, EMA, AAO, NANOS, or AOA.

As people lose weight and get healthier on GLP-1 medicines, their blood pressure and cholesterol medicines are often not reviewed or adjusted. Blood pressure treatment that is no longer matched to a person’s needs may lead to low blood pressure (hypotension). Low blood pressure can be more pronounced at night and could reduce blood flow to the optic nerve during sleep. That possibility would fit the typical way NAION presents: vision loss noticed on waking.

Dr. Deom recommends that people taking a GLP-1 medicine also work on exercise and diet, and keep regular visits with their usual doctors — even if that doctor did not prescribe the GLP-1 — so the rest of their care, including blood pressure, is maintained. Do not start, stop, or change a blood pressure or cholesterol medicine on your own; talk with the clinician who prescribes it.

How to reach us

Hazleton Eye Specialists: phone 570-453-2020, fax 570-453-1020. Addresses for all five offices (Hazleton, Stroudsburg, Nanticoke, Pottsville, and Bangor) are on Find an Eye Doctor.

Sudden vision loss needs same-day care. Call an eye doctor right away. If you also have a new headache, jaw pain when chewing, scalp tenderness, fever, or you are over 50 and feel unwell, go to the emergency department.

Sources

American Academy of Ophthalmology. What Is Optical Coherence Tomography? https://www.aao.org/eye-health/treatments/what-is-optical-coherence-tomography
Biousse V, Newman NJ. Diagnosis and clinical features of common optic neuropathies. Lancet Neurol. 2016;15(13):1355-1367.

Medical disclaimer. This page is for general education only. It is not medical advice and does not replace an examination or a conversation with your own doctors. Do not start, stop, or change any medicine without talking to the clinician who prescribes it. If you have sudden vision loss, seek same-day care from an eye doctor or an emergency department. Information is current as of the “last reviewed” date and may change as new research is published.