Which portion of the optic nerve is not myelinated?

Which portion of the optic nerve is not myelinated?

• A. Intraocular
• B. Intraorbital
• C. Intracanalicular
• D. Intracranial

Answer: (A)

The nerve fibers in the eye aren’t myelinated yet. Myelin on the optic nerve fibers is produced by oligodendrocytes, but this wrapping begins only after the fibers pass through the lamina cribrosa at the optic disc. The intraocular portion lies in front of that boundary, inside the eyeball, so it remains unmyelinated. In contrast, the portions behind the lamina cribrosa—the intraorbital, intracanalicular, and intracranial segments—are myelinated as they travel through the orbit, the skull, and toward the brain.

The nerve fibers in the eye aren’t myelinated yet. Myelin on the optic nerve fibers is produced by oligodendrocytes, but this wrapping begins only after the fibers pass through the lamina cribrosa at the optic disc. The intraocular portion lies in front of that boundary, inside the eyeball, so it remains unmyelinated. In contrast, the portions behind the lamina cribrosa—the intraorbital, intracanalicular, and intracranial segments—are myelinated as they travel through the orbit, the skull, and toward the brain.