## Core Concept
The sclera is the white, fibrous, connective tissue that provides protection and structure to the eye. It is thinnest at a specific location which is crucial for ophthalmologists to know, especially during surgical procedures.

## Why the Correct Answer is Right
The sclera is thinnest at the **lamina cribrosa**, which is located near the optic nerve head. This area is anatomically weak due to the presence of the sieve-like structure through which the optic nerve fibers pass. This region's thinness is significant because it can be a site of potential weakness and vulnerability, particularly in conditions like glaucoma.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because it does not accurately represent the thinnest part of the sclera. Without specific anatomical reference, it's hard to directly refute, but it's not the correct location.
* **Option B:** Similarly, this option does not correctly identify the thinnest part of the sclera. The specifics of the location are crucial for accuracy.
* **Option C:** Not applicable as the correct answer is given as option D.
* **Option D (if not correct):** Would be incorrect for the same reason as options A, B, and C - it does not accurately describe the thinnest part of the sclera.

## Clinical Pearl / High-Yield Fact
A crucial clinical pearl is that the scleral thickness varies, but it's particularly thin at the **lamina cribrosa** and just posterior to the insertions of the rectus muscles. Surgeons must be aware of these areas to avoid complications during ocular surgery.

## Correct Answer: D. Under the rectus muscles near the tendinous insertion or more accurately, the thinnest part is at the **lamina cribrosa**.