Correct Answer: D. None of the above
Horner's syndrome produces mild ptosis (1–2 mm) due to selective paralysis of Müller's muscle (superior tarsal muscle), which is innervated by sympathetic fibres. The levator palpebrae superioris remains fully intact and functional. The definitive surgical treatment for Horner's ptosis is Müller's muscle–conjunctival resection (MMCR), a procedure guided by a positive phenylephrine test (instillation of 2.5–10% phenylephrine temporarily corrects the ptosis by directly stimulating Müller's muscle, confirming sympathetic denervation). MMCR is the gold-standard operation for this condition and is not listed among the options, making "None of the above" the correct answer.
It is important to distinguish MMCR from the Fasanella–Servat procedure. Although both target the posterior lamella, the classic Fasanella–Servat operation resects a non-selective strip of conjunctiva, Müller's muscle, and the superior tarsal border (tarsus), making it a less precise technique. Modern practice favours MMCR, which spares the tarsus and is specifically indicated when the phenylephrine test is positive — the hallmark of Horner's syndrome. Because MMCR is the evidence-based, preferred procedure and is absent from the option list, none of the three listed operations qualifies as the correct treatment.
Why other options are wrong
- A. Levator resection — Reserved for moderate-to-severe ptosis (>3 mm) with poor levator function, such as aponeurotic ptosis, myasthenia gravis, or oculomotor nerve palsy. In Horner's syndrome the levator is normal; resecting it constitutes overtreatment and risks an unnatural eyelid contour.
- B. Frontalis sling — Indicated only for severe ptosis with absent or markedly reduced levator function (e.g., congenital ptosis with levator agenesis, CPEO). Since levator function is fully preserved in Horner's syndrome, a frontalis sling is entirely inappropriate and would produce abnormal eyelid dynamics.
- C. Fasanella–Servat operation — Although it addresses the posterior lamella and Müller's muscle, it non-selectively resects the superior tarsus as well. Current ophthalmic practice has largely replaced it with the more precise MMCR for Horner's ptosis. The Fasanella–Servat procedure is therefore not the treatment of choice and does not represent the best answer.