Involutional Ptosis

The most commonly acquired ptosis is age-related ptosis (Fig. 28.2). There is ongoing debate about the underlying pathogenesis of involutional ptosis. Jones and others^9–13 proposed that involutional ptosis is caused by disinsertion of the levator aponeurosis from tarsus, so reattachment of the dehisced edge should correct the problem (Fig. 28.3). However, a detached edge cannot be identified in all cases. Nevertheless, many cases of “involutional” ptosis can be satisfactorily corrected with levator advancement well into the aponeurosis or even into the muscle itself. Carroll et al. could not identify defects in the aponeurosis and postulated that the dehiscence and disinsertion seen by others was largely iatrogenic.^15,16 In many cases, fat is present in the levator muscle and/or Müller muscle, suggesting that many cases of “involutional” ptosis represent a form of muscular degeneration, be it pathologic or simply age-related muscle mass loss. Supporting evidence that a myogenic etiology might be the underlying problem comes from a report showing that levator function in patients with involutional ptosis is reduced.²⁹ Disinsertion or thinning of the aponeurosis does not explain all cases of involutional ptosis. Although some cases do undoubtedly reflect physical aponeurotic pathology, at least some patients likely have a myogenic component as the major contributor. The cause of age-related ptosis is not clear despite common dogma to the contrary.

Normal “levator function” is not easy to quantify. A slow 12-mm lid margin excursion may not be “normal” in some age groups. Certainly, it is different and discernable from a quick 15-mm excursion. Lid margin excursion may be the best clinical tool we have to estimate the health of the levator complex, but it is a rough estimate of function, as we cannot easily measure velocity, acceleration, or force. Additional research on this topic is needed, but since standard surgeries improve the eyelid height in most patients, there has been little urgency to investigate the etiology further (Fig. 28.4).

Controversy: One commonly cited cause of aponeurosis disinsertion is long-term contact lens wear. This idea was based on a small number of cases reported in the 1970s but has not been corroborated. Given the number of long-term contact lens wearers, one would expect to see more contact lens–related ptosis cases if there were causation. Those supporting the contact lens theory of aponeurotic ptosis link it more closely to hard or rigid gas-permeable contact lens wear; wearers are instructed to drag the lid laterally and squeeze the orbicularis when removing the lens. However, even soft contact lens wearers have a demonstrable higher tendency toward ptosis.³⁰

Neurogenic Ptosis

Unilateral ptosis in combination with pupillary abnormalities may be caused either by disruption in the sympathetic pathway or by an oculomotor nerve palsy (Fig. 28.5). Horner syndrome comprises a triad of findings: ptosis, miosis, and anhidrosis on one side, caused by a defect in the sympathetic pathway (Fig. 28.6). A lesion anywhere along the sympathetic pathway can lead to decreased Müller muscle tone, causing a ptosis typically of 1 to 2 mm. Anisocoria that is more pronounced in dim light should prompt pharmacologic testing to confirm Horner syndrome. An acute onset Horner syndrome can be caused by carotid dissection and should be urgently evaluated (see below). Complete third cranial nerve palsy causes unilateral ptosis, mydriasis, and limited adduction, supraduction, and infraduction. Partial or incomplete third nerve palsy can also occur and does not always involve the pupil; pupil-sparing oculomotor palsy is more likely to result from ischemia.

Myasthenia gravis (MG) is another rare cause of ptosis, in which autoantibodies block transmission of neuroelectrical signals at the neuromuscular junction. Although MG is a systemic disease, many patients initially present with symptoms of ptosis or diplopia. Autoantibodies variably affect different extraocular muscles, leading to intermittent diplopia. This may cause a noncomitant strabismus pattern that can vary from day to day. MG is sometimes classified as a form of myogenic ptosis, but because the muscle itself is not abnormal (as in the case of other myogenic ptoses), this neuromuscular junction disorder is more appropriately grouped with neurologic disorders (Fig. 28.7).

Myogenic Ptosis

Myogenic ptosis refers to a dystrophic condition that is primary to the muscular tissue. It may represent a failure of muscle development, as in congenital ptosis, or it may be acquired, as in oculopharyngeal dystrophy. In either case, the effect is a focal form of muscular dystrophy that prevents effective contraction of muscle fibers, typically leaving a fatty or fibrous tissue in place of healthy striated muscle (Fig. 28.8).

Most forms of sporadic or syndromic congenital ptosis are myogenic and are reviewed in detail in Chapter 8.

Adult-onset myogenic ptosis may be caused by mitochondrial myopathies, oculopharyngeal dystrophy, and myotonic dystrophy.

Mitochondrial disease is a group of disorders caused by dysfunctional mitochondria, the organelles that produce energy for the cell. This usually results from sporadic mutations in mitochondrial DNA, specialized circular DNA containing 37 genes that code for Krebs cycle enzymes. This circular DNA replicates within mitochondria that are inherited entirely from the mother. Mutations in nuclear DNA genes that code for mitochondrial proteins may also result in these diseases.

Mitochondrial myopathies constitute a subgroup that specifically causes neuromuscular weakness, of which the most common manifestation is chronic progressive external ophthalmoplegia (CPEO). CPEO is characterized by slowly progressive paralysis of the extraocular muscles, usually associated with preceding progressive bilateral upper lid ptosis. It may occur as an isolated syndrome or in association with skeletal muscle weakness. The isolated variant typically develops in the fifth or sixth decade.

Kearns-Sayre syndrome (KSS) is a mitochondrial myopathy with onset before age 20 years manifesting with CPEO, pigmentary retinopathy, and one or more of cardiac conduction defects, cerebrospinal fluid (CSF) elevated protein, or a cerebellar syndrome. Other abnormalities in KSS include mental retardation, hearing loss, seizures, and endocrine disorders³ (Fig. 28.9).

CPEO may also be a sign in oculopharyngeal dystrophy, myotonic dystrophy, or myasthenia gravis.

Myotonic dystrophy usually presents clinically during the teens or early twenties. Patients may manifest additional ocular signs including refractile lenticular deposits (“Christmas tree cataract”), pigmentary retinopathy, or ophthalmoplegia.

Oculopharyngeal muscular dystrophy (OPMD) typically presents in the seventh decade of life. Patients develop ptosis, facial muscle weakness, and progressive dysphagia. A family history is present, often associated with a French Canadian pedigree. OPMD is inherited as an autosomal dominant somatic mutation.

Mechanical Ptosis

Ptosis caused by a local mass effect is considered mechanical ptosis. A benign neoplasm, edema, or even a chalazion in the upper eyelid can weigh or push the eyelid down. Usually, a mass or edema is easily identified as the cause of ptosis, and when treated appropriately, the eyelid position reverts to normal (Fig. 28.10).

Traumatic Ptosis

Injury to the upper eyelid may damage the levator or its aponeurosis, especially given the thinness of the upper lid. Blunt or sharp trauma causing preaponeurotic fat herniation should raise suspicion of underlying levator laceration or hematoma: this can be tested by measuring the levator function if the patient is conscious. Scar tissue following trauma may cause limited lid excursion, causing both ptosis and eyelid lag. Traumatic third nerve palsy is usually classified as neurogenic. Certain ocular surgeries, including retinal, glaucoma, and anterior segment surgeries, may lead to postoperative ptosis that may be transient or permanent. This may be caused by the eyelid speculum pulling the eyelid up while the eye is infraducted, causing a stretching of the aponeurosis from its tarsal insertion site. This type of ptosis is less commonly seen with the elimination of a superior rectus traction suture (Fig. 28.11).

Pseudoptosis

A number of eyelid conditions can mimic ptosis and potentially mislead the clinician. Common causes include severe enophthalmos with narrowing of the palpebral fissure, ipsilateral hypotropia, brow ptosis, and contralateral lid retraction giving the impression of relative ptosis of the opposite lid. The most common cause is dermatochalasis that reduces the true margin reflex distance by mechanical effect or the functional margin reflex distance by overhanging the lid margin proper. These cases are confirmed when the lid height returns to normal after simple blepharoplasty without surgical repair of the ptosis (Fig. 28.12).