## Core Concept
The sclera is the white, fibrous, outer layer of the eyeball, providing protection and structure. Its thickness varies, being thickest at the posterior aspect near the optic nerve and thinnest under the rectus muscles. This anatomical variation is crucial for understanding various ophthalmological conditions and procedures.

## Why the Correct Answer is Right
The sclera is thickest at the **equator** and particularly **posteriorly**, but specifically, it reaches its maximum thickness around the **optic nerve** insertion site. However, when considering general anatomical references and common descriptions in ophthalmology, the sclera is notably thick at its posterior aspect. This thickness provides significant protection to the eye, especially considering the insertion of extraocular muscles and the passage of the optic nerve.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, although the sclera does have varying thickness, the specific location provided does not accurately represent the thickest part.
- **Option B:** This option is incorrect as it does not accurately describe the anatomical location where the sclera is thickest.
- **Option C:**
- **Option D:** This option is incorrect because it inaccurately represents the location of maximum scleral thickness.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the sclera is thinnest under the rectus muscles, which is an important consideration during ocular surgeries to avoid globe injury. The thickest part being posteriorly, near the optic nerve, highlights the protective mechanism of the sclera around vital structures.

## Correct Answer: C. Posterior part near the optic nerve.