**Core Concept**
The Fasanella-Servat operation is a surgical procedure aimed at treating ptosis (drooping eyelid) by shortening the superior tarsal muscle (m. levator palpebrae superioris). This procedure is typically indicated in cases of mild to moderate ptosis where the levator muscle is intact but weak.

**Why the Correct Answer is Right**
The Fasanella-Servat operation involves the resection of a small portion of the Müller's muscle (superior tarsal muscle) to tighten the eyelid. This procedure is effective in mild to moderate cases of ptosis because it helps to improve the eyelid's position without compromising the function of the levator muscle. However, it is not suitable for cases with significant levator muscle weakness or in patients with severe ptosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Fasanella-Servat operation is not typically performed in cases of severe ptosis, where a more extensive procedure like a frontalis sling operation may be required.
**Option B:** This option is incorrect because the procedure involves resection of Müller's muscle, not tarsal plate resection, which is a different surgical approach.
**Option C:** This option is incorrect because the Fasanella-Servat operation is specifically indicated for mild to moderate ptosis, not for cases with significant levator muscle weakness.

**Clinical Pearl / High-Yield Fact**
The Fasanella-Servat operation is a useful procedure for treating mild to moderate ptosis, but it is essential to carefully select patients who would benefit from this procedure, as it may not be suitable for all cases of ptosis.

**Correct Answer: D.**