Ocular Ptosis and Its Differential Diagnosis

Ptosis, or blepharoptosis, is a decrease in the eyelid opening, or palpebral aperture. The condition can be either congenital or acquired. Ptosis typically refers to a lack of normal opening of the upper eyelid, resulting in its downward drooping.¹ Less commonly, there can also be a lack of normal opening of the lower eyelid, resulting in its upward placement, referred to as inverse or reverse ptosis.²

UNDERSTANDING PTOSIS

Acquired ptosis can be caused by a number of etiologies, ranging from those related to normal aging changes to potentially life-threatening conditions. Generally, ptosis can be filed into one of the following categories: aponeurotic, traumatic, mechanical, myogenic, or neurogenic¹ (see Categories of Acquired Ptosis). Because ptosis can be a harbinger of a possible serious underlying neurologic condition (Table), it is imperative to be able to identify the slightest degree of ptosis, even in an asymptomatic individual, because the magnitude of ptosis does not indicate its etiology.

Eyelid Measurements

Although eyelid asymmetry is often an indicator of ptosis, it need not be present; ptosis can be unilateral or bilateral. Eyelid measurements (Figure 1) and assessment of eyelid function are imperative to accurately diagnose ptosis. These can easily be performed as part of a comprehensive eye examination. Typically, ptosis is identified by measuring palpebral apertures and/or marginal reflex distance-1 (MRD-1).^1,3

Palpebral aperture is the distance from upper eyelid margin to lower eyelid margin. MRD-1 is the distance from the upper eyelid margin to the corneal light reflex produced from shining a light into the eyes.^1,3 In order to ensure an accurate measurement for both of these tests, it is important to immobilize the frontalis muscle. To do so, place the palm of one hand on the patient’s forehead with a bit of downward pressure to stop him or her from raising the upper lids by use of the frontalis muscle (Figure 2). For both of these measurements, the patient should be looking straight ahead with no head or chin tilt.

Additional eyelid measurements include eyelid crease and levator function. The eyelid crease represents the insertion of the levator aponeurosis into the upper eyelid; it can be measured as the distance from the upper eyelid margin to the eyelid crease when the patient is looking down. Note that there can be more than one eyelid crease on each side and that disinsertion of the levator aponeurosis results in a larger measurement or greater distance from the upper eyelid margin. Levator disinsertion, or aponeurotic ptosis, can occur as a result of normal aging or from excessive eye rubbing or tugging, as in repetitive rigid contact lens removal.^1,3

Levator function is defined as maximum excursion of the upper eyelid from downgaze to upgaze and is measured by having the patient look down as far as possible and placing the reference point of a ruler so that it is contiguous with the upper eyelid margin. Without moving the ruler and without the patient moving his or her head, have the patient look up as far as possible. Where the upper eyelid margin now intersects the ruler (the distance the upper lid margin traveled from downgaze to upgaze) equals the levator function.^1,3

Eyelid Anatomy

Levator Palpebrae Superioris

The levator palpebrae superioris is the strongest of two eyelid muscles that function to open the upper eyelid. It is innervated by the third cranial nerve. Therefore, damage to the levator muscle itself, to its aponeurotic insertion into the upper eyelid, to the third cranial nerve, or to the neuromuscular junction between the muscle and the nerve (as impaired in myasthenia gravis) can each result in a ptotic upper eyelid. Damage to any of these structures related to the levator palpebrae superioris may result in any degree of ptosis, from slight to complete eyelid closure.^1,4

Superior Tarsal Muscle

The second eyelid muscle that normally functions to open the upper eyelid is the superior tarsal muscle, also known as the Müller muscle. It originates from the undersurface of the levator palpebrae superioris and inserts into the superior tarsal plate. The Müller muscle plays only a small role in opening the upper eyelid; therefore, damage to it or to its sympathetic autonomic innervation results in only a small degree of ptosis of the upper eyelid.

Inferior Tarsal Muscle

Unlike the levator palpebrae superioris, the superior tarsal muscle has a companion muscle that acts to open the lower eyelid. The inferior tarsal muscle inserts into the inferior tarsal plate and is also under sympathetic autonomic innervation. Therefore, neurologic sympathetic autonomic damage, as in Horner syndrome, may result in both a small upper eyelid ptosis and a small lower eyelid reverse ptosis.^1,4,5

DIFFERENTIAL DIAGNOSES

Horner Syndrome

Because sympathetic autonomic innervation involves not only the tarsal muscles but also the iris dilator muscle, it is equally important to measure pupil size in both bright and dim illumination. A small degree of ptosis in the setting of anisocoria greatest in dim illumination, or even just a smaller pupil on the same side of the ptosis, should raise suspicion for Horner syndrome.

To prove that Horner syndrome is present in a nonacute and nonpainful setting, diagnostic testing with 0.5% or 1.0% apraclonidine is key. A reversal of anisocoria, in which the smaller pupil in the ptotic eye becomes the larger of the two pupils within 1 hour after instillation of the apraclonidine in both eyes, is diagnostic of Horner syndrome.

In cases of suspicious Horner syndrome that is acute and/or painful, diagnostic drops should be withheld and the patient should be sent immediately to the emergency department for neuroimaging (CT angiography or MR angiography) to rule out carotid dissection.^1,6-8

Third Cranial Nerve Palsy

The other potential scenario requiring emergent neuroimaging in the setting of ptosis is a third cranial nerve palsy because it could be suggestive of a posterior communicating artery aneurysm. Aside from any degree of ptosis, other clinical features may include limitation of supra-, infra-, and adductions, with a corresponding reversing hyperdeviation and exodeviation that worsens when looking contralaterally to the side of the ptosis. In addition, because parasympathetic autonomic fibers travel on the outside of the third cranial nerve, a larger pupil on the side of the ptosis and/or anisocoria greater in bright illumination can also be clinical features concerning for an aneurysmal third cranial nerve palsy.^9,10

Myasthenia Gravis

In the setting of a ptosis, it is critical to perform not only pupil size measurements in both bright and dim illumination but also ductions and cover testing in multiple positions of gaze. Another cause of ptosis combined with abnormal motilities is myasthenia gravis. Although myasthenia gravis does not cause pupillary abnormalities, it can cause other telltale clinical findings such as weakness of the orbicularis oculi muscle and positive results on fatigue and ice pack tests. Suspicion of myasthenia gravis usually requires outpatient workup and neurology referral, but it can be emergent in the setting of a myasthenic crisis.^1,11-13

Pseudoptosis

When dealing with an eyelid asymmetry, it is also helpful to take exophthalmometry measurements because pseudoptosis can be caused by enophthalmos of the eye with the smaller palpebral aperture, or by proptosis and/or eyelid retraction of the fellow eye. Another common cause of pseudoptosis is dermatochalasis.¹

TREATING PTOSIS

Careful history-taking and past photo review, along with detailed measurements of efferent visual function, as noted above, can help determine how to characterize ptosis, the need for additional workup, urgency, and potential treatment options. After concerning underlying etiologies are excluded, the focus can be placed on treatment. Although surgery has been the mainstay of ptosis treatment to date, there is now a new option: preservative-free oxymetazoline HCl ophthalmic solution 0.1% (Upneeq, RVL Pharmaceuticals), which was approved by the FDA last year for the treatment of acquired blepharoptosis. This ophthalmic alpha-adrenergic agonist can be instilled once daily to raise the upper eyelid and improve superior visual field by activating the superior tarsal muscle.¹⁴

STAY ONE STEP AHEAD

Eye care providers should assess all patients for possible ptosis, even those who are asymptomatic. Making eyelid assessment a regular part of comprehensive eye examinations can have a positive effect on your patients’ quality of life in terms of morbidity and mortality as well as visual function and cosmesis.