## Core Concept
The optic nerve is a crucial part of the visual pathway, transmitting visual information from the retina to the brain. Its length can vary but is generally considered to be approximately 50-60 mm. Understanding the anatomy of the optic nerve is essential for diagnosing and managing various ophthalmological conditions.

## Why the Correct Answer is Right
The correct length of the optic nerve is approximately **50-60 mm**. This range accounts for the variations in human anatomy and the fact that the nerve runs from the eyeball, through the orbit, and into the cranial cavity. This length allows for the necessary transmission of visual signals without compromising the structural integrity of the eye or the brain.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately reflect the known anatomical length of the optic nerve.
- **Option B:** Similarly, this option does not match the established range for the length of the optic nerve.
- **Option D:** This option also does not align with the recognized anatomical measurements of the optic nerve.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the optic nerve is not a true nerve but rather a **cerebral tract** or **projection** of the central nervous system (CNS). It is crucial for transmitting visual information and its damage can lead to various visual impairments.

## Correct Answer: C. 50-60 mm.