Mullerectomy: Indications, Anatomy, and Surgical Steps

Mullerectomy is a surgical procedure used to correct mild to moderate eyelid ptosis by targeting Müller’s muscle. It provides a less invasive alternative to levator resection, offering quicker recovery and predictable outcomes. This procedure is particularly effective for patients who respond well to phenylephrine testing, which assesses involuntary muscle function to determine candidacy.

Anatomy Of Muller’s Muscle

Müller’s muscle, or the superior tarsal muscle, is a thin layer of smooth muscle in the upper eyelid. It originates from the undersurface of the levator palpebrae superioris and inserts into the superior tarsal plate. Unlike the levator muscle, which is under voluntary control, Müller’s muscle is innervated by the sympathetic nervous system, contributing to involuntary eyelid elevation. This autonomic control helps maintain eyelid position during alertness and emotional responses.

The muscle receives innervation from postganglionic sympathetic fibers originating in the superior cervical ganglion. These fibers travel along the internal carotid artery and enter the orbit via the ophthalmic division of the trigeminal nerve. Disruptions in this pathway, such as in Horner’s syndrome, can cause mild ptosis due to the loss of sympathetic tone, making Müller’s muscle a useful target for surgical correction when levator function is intact.

Histologically, Müller’s muscle consists of smooth muscle fibers interspersed with connective tissue, allowing it to maintain tonic contraction. It is structurally distinct from the striated levator palpebrae superioris, which provides the primary force for eyelid elevation. The muscle’s attachment to the superior tarsal plate enables subtle yet functionally significant eyelid elevation, typically contributing 1 to 2 mm of lift. This modest role in eyelid positioning makes it a key target for procedures that refine eyelid height without extensive tissue disruption.

Indications In Eyelid Ptosis

Mullerectomy is indicated for patients with mild to moderate ptosis who show a favorable response to phenylephrine testing. This test involves applying a 2.5% or 10% phenylephrine solution to the conjunctival surface, temporarily stimulating Müller’s muscle. A positive response—defined as at least 2 mm of eyelid elevation—suggests ptosis is due to insufficient Müller’s muscle tone rather than significant levator dysfunction. Patients with a poor response may require levator resection instead.

Acquired ptosis, particularly due to age-related changes, often involves mild Müller’s muscle dysfunction while levator function remains adequate. In these cases, weakening sympathetic input leads to subtle eyelid drooping. Since the levator remains functional, enhancing Müller’s muscle contribution can restore eyelid height without aggressive surgery. This approach offers a shorter recovery period and reduces the risk of postoperative lagophthalmos.

Patients with mild ptosis from conditions affecting sympathetic innervation, such as Horner’s syndrome, may also benefit. The characteristic 1 to 2 mm ptosis in these cases aligns with the degree of elevation achieved through Mullerectomy. While the procedure does not address the underlying neurological cause, it improves visual field and aesthetic symmetry. However, patients with ocular motility disturbances or significant levator impairment may not achieve optimal results.

Surgical Approach

Mullerectomy is performed through a posterior approach, allowing direct access to Müller’s muscle without external incisions. The procedure begins with eyelid eversion using a Desmarres retractor to expose the conjunctival surface. Local anesthesia with epinephrine minimizes bleeding and enhances precision. The surgeon identifies the junction between Müller’s muscle and the conjunctiva, ensuring excision remains within the targeted tissue plane.

Precise tissue resection is critical for achieving the desired eyelid elevation. Removing approximately 8 to 10 mm of Müller’s muscle and conjunctiva typically results in a 2 mm lift, though individual anatomy influences this outcome. A Putterman clamp is often used to secure the tissue before excision, providing controlled resection and minimizing bleeding. The clamp also reduces the need for cauterization, which can cause excessive scarring or discomfort.

After excision, meticulous hemostasis is ensured before closure. A running or interrupted absorbable suture is commonly used to approximate the conjunctiva and remaining Müller’s muscle, maintaining structural integrity and promoting smooth healing. Some surgeons use fibrin glue to reduce inflammation and enhance tissue adhesion, though its long-term benefits remain under investigation. The eyelid is repositioned and assessed for symmetry before concluding the procedure.

Postoperative Eye Physiology

Following Mullerectomy, eyelid positioning adjusts as muscle tension redistributes. In the immediate postoperative period, mild edema and conjunctival inflammation can temporarily affect lid height. As healing progresses, the remaining muscle fibers and connective tissue adapt, stabilizing the eyelid at its new position.

Tear film distribution may be affected, as the eyelid plays a key role in spreading and maintaining the tear film. Changes in lid position can influence blink rate or completeness, leading to temporary dryness or irritation. Most patients compensate with increased reflex tearing, though those with preexisting ocular surface disease may require lubricating drops. Studies indicate Mullerectomy has a lower incidence of postoperative dry eye than levator resection, but monitoring tear stability remains essential.