Aponeurotic ptosis is a condition that results from a localized or generalized true disinsertion of the levator aponeurosis. Alternatively, it may be due to a weakening and attenuation of the distal levator aponeurosis fibers without frank disinsertion.³ It may be age-related (involutional) or may occur due to a variety of factors, including trauma, repeated eyelid edema (blepharochalasis), long-term contact lens wear, chronic eyelid rubbing, postsurgical changes, or floppy eyelid syndrome.¹,³,⁴,⁵,⁶,⁷ In the young population, trauma-related aponeurotic ptosis is the most common cause.¹ Contact lens use with or without associated giant papillary conjunctivitis is another frequent cause of aponeurotic disinsertion.¹ Postsurgical or postoperative ptosis is an acquired ptosis that occurs after intraocular surgery, which was a significant issue in the past. However, its frequency has been decreasing as cataract surgery and anesthetic techniques have evolved, a fact which is reflected by the sharp decline in the number of publications discussing the subject since the advent of phacoemulsification.⁵,⁷ The etiology of postcataract ptosis is poorly understood but is probably multifactorial. Postoperative levator muscle/aponeurotic injury could occur due to mechanical forces, myotoxicity, and/or neurotoxicity.⁷ Mechanisms proposed in the past to cause this complication include eyelid edema, bridle suture placement, superior rectus grasping, size and location of the surgical incision, peribulbar or retrobulbar anesthesia, prolonged patching, and ocular massage, but most of these are no longer performed with modern phacoemulsification techniques. However, other factors such as a preexisting narrower vertical palpebral aperture, eyelid speculum placement, previous intraocular surgery, and most importantly, a reduced preoperative levator function may still play a role.⁷

Cadaveric and histologic studies show direct as well as indirect evidence of attenuation of the aponeurosis as the etiopathogenetic mechanism behind aponeurotic ptosis.⁶,⁷,⁸,⁹ Direct evidence includes thinning, stretching, and disinsertion of the levator from its attachments to the tarsus and pretarsal orbicularis muscle.⁶,⁷,⁸,⁹,¹⁰ When the distal end of the aponeurosis is missing in histologic specimens, this is considered indirect evidence of an aponeurotic event.⁸ Another anatomic change in aponeurotic ptosis which is seldom referred to in the literature despite its surgical relevance is an age-related thinning and dehiscence of the medial limb of Whitnall ligament and the medial horn of the levator, resulting in a lateral or anterolateral displacement of the tarsus.¹⁰,¹¹ In a recent study on senile Asian cadavers, the average width of the medial horn of the levator was 6.0 mm while that of the lateral horn was 12.3 mm making it more vulnerable to age-related redundancy. If not specifically addressed, these changes may subsequently cause medial undercorrection after ptosis surgery.¹⁰,¹¹ Of note is that a recent clinicopathologic study showed evidence of muscle damage and decreased muscle fiber bulk in patients with aponeurotic ptosis.⁵ These findings suggest that even though it is believed that the levator muscle is preserved in aponeurotic ptosis on a macroscopic level, there is an ongoing process of muscle damage on the microscopic level, and further research is necessary to fully understand its role in the pathogenesis of aponeurotic ptosis.⁵

Intuitively, aponeurotic changes should be the only expected histopathologic findings in patients with aponeurotic ptosis, and indeed some studies do show a normal levator
muscle. However, other histologic studies have documented atrophy, and fibrosis, as well as fatty infiltration of the levator muscle, suggesting a possible age-related myopathic process as a component in the pathogenesis of this condition.⁶,⁹ Whether these changes do play a role in the pathogenesis of aponeurotic ptosis is controversial, and two alternative explanations exist for those degenerative levator muscle abnormalities, and both are entirely plausible. Sarcopenia or loss of muscle mass and strength as a consequence of aging is a universal finding throughout the body, and there is no reason to believe the levator should be an exception. Alternatively, this fatty infiltration of the levator muscle could be a degenerative response to long-standing aponeurotic disinsertion.⁶,¹⁰,¹² Atrophic changes are also observed in the Müller muscle itself, which becomes thinner and more elongated, shows significant fatty infiltration with advancing age, and may even migrate from the superior tarsal border. As we shall see later, these changes have implications for interpreting the results of phenylephrine testing.¹²,¹³,¹⁴,¹⁵,¹⁶

Aponeurotic ptosis is by far the commonest type of ptosis, and although frequently termed “senile” or “involutional” blepharoptosis in the literature, the former is a clear misnomer, and in general, the use of both terms may be confusing since aponeurotic ptosis may occur at any age including neonates.¹⁷,¹⁸ Important measurements and definitions have to be clarified before describing the clinical picture of aponeurotic ptosis which is crucial for surgical planning. The palpebral fissure height (PFH) is defined as the distance between the upper and lower lid margins while the patient is looking in primary gaze (normal range can vary from 7 to 12 mm).⁴,¹⁹,²⁰,²¹,²² The amount of ptosis in mm is calculated by subtracting the PFH value on the normal side from that on the ptotic side in unilateral cases and from a reference value of 10 in bilateral cases. The problem with such measurements is that it is assumed that the lower eyelid is normal in position, which is not always the case. Therefore, the superior margin to reflex distance (MRD1) is more accurate.¹⁹,²⁰ MRD1 is defined as the distance between the upper eyelid margin and the corneal light reflex or the pupillary center; the normal value is 3.5 to 5 mm. MRD1 is assigned a negative value if the eyelid margin lies below the corneal light reflex. MRD2 is the distance from the margin of the lower lid to the central corneal reflex; normal is 4 to 5 mm.⁴,¹⁹,²⁰,²¹,²² The normal position of the upper eyelid crease is 7 to 10 mm above the eyelid margin.³ The most important measurement to make during the examination of a ptosis patient is the levator muscle function or the range of excursion of the eyelid margin from extreme down-gaze to extreme up-gaze. The normal function ranges from about 13 to 16 mm.² Except in patients with Horner syndrome where the MRD2 may be reduced, MRD2 is of little clinical significance in actual clinical practice, and physicians rely more on the MRD1 and PFH, the former being the more clinically accurate.³ To obtain accurate measurements of the levator muscle function, PFH, and MRD1, it is important to assure that the frontalis muscle is completely neutralized by pressing the brow firmly against the superior orbital rim.²,²¹,²³

Although the clinical diagnosis of ptosis is relatively simple and can be made from a routine clinical examination, to plan appropriate management proper identification of the cause of the ptosis is important, and often requires a thorough history taking, not just from the patient but from family members as well even if the patient was an adult.¹ History taking should retrieve the following information: age of onset, family history, prior intraocular or eyelid surgery, predisposing factors such as contact lens wear or trauma, recurring episodes of eyelid swelling, whether the ptosis worsens throughout the day, the presence of any aberrant eyelid positions with facial movements, and if there is double vision. Past medical history as well as a list of current medications, including the use of blood-thinning products, is also important.²⁴

Patients with aponeurotic ptosis present with an upper eyelid that is lower in position than normal (Figure 8.1), with an elevated or absent eyelid crease (Figure 8.2).⁶ By definition, the levator muscle function is usually ≥10 mm and generally exceeds 12 mm, but in contrast to myopathic dysgenetic ptosis (Chapter 10), there is no correlation between PFH and levator muscle function.⁵,²⁵ The ptosis is constant in all positions of gaze including downgaze, and it may become more noticeable by the end of the day when the patient is tired. Thinning of the eyelid with a deep upper eyelid sulcus (Figure 8.3) can also be observed in more severe cases.⁴ This is often associated with a compensatory brow elevation due to the unconscious recruitment of the ipsilateral frontalis muscle to help raise the eyelid from its lower resting position and increase the superior visual field (Figure 8.4).²⁶,²⁷ In unilateral cases, compensatory contralateral pseudoretraction may be observed due to the Hering law (Figure 8.5), and for the same reason, contralateral ptosis might develop postoperatively.²⁸,²⁹ Therefore, Hering law dependency should be tested in every patient as it has been demonstrated in ≥50% of aponeurotic ptosis patients (Figure 8.6).³⁰ The test for the Hering phenomenon can be performed by manually elevating the ptotic eyelid to a normal position,³⁰ or by pharmacologic elevation of the ptotic eyelid with 2.5% or 10% phenylephrine.²⁹,³¹

When aponeurotic ptosis is suspected, the phenylephrine test is often performed. Phenylephrine is an alpha-1 adrenergic agonist that contracts the sympathetically innervated Müller muscle, a secondary eyelid retractor, and elevates the eyelid.²³ The first step in this test involves measuring the MRD1, preferably with photographic documentation, followed by instillation of 1 drop of 2.5% or less commonly 10% phenylephrine in the superior conjunctival fornix or on the superior limbus of the ptotic eye, with the eye looking down.²³ After a waiting period of 3 to 5 minutes, the MRD1 is measured again.²³ If phenylephrine results in an improvement in eyelid height of >2 mm, this is considered a positive

response, but if the eyelid lift is <2 mm this is considered a negative or poor response.¹⁵ The 2.5% is preferred by many oculoplastic surgeons because it has nearly the same efficacy as 10%, without the side effects.¹⁵,³²,³³ Adrenergic side effects can include cardiac arrhythmias, myocardial infarction, severe hypertension, pulmonary edema, and even cardiac arrest or subarachnoid hemorrhage.¹⁵ The difference in eyelid lift between the 2.5% and 10% concentrations is within the range of 0.2 mm, which is clinically irrelevant and therefore does not justify the use of the higher concentration.¹⁵,³³ Patients with mild ptosis have the greatest response rate and the highest degree of eyelid elevation, while patients with severe ptosis may not respond well to the test and are therefore considered poor candidates for Müller muscle conjunctival resection surgery (MMCR).³,²³ The phenylephrine test may also be important in deciding whether to operate on one or both sides, as patients with unilateral ptosis who manifest Hering dependency in the contralateral eyelid after phenylephrine testing may be considered for bilateral surgery.³⁴

Although a good response to the phenylephrine test is useful and is a necessary prerequisite MMCR,²²,²³,³⁵ there are certain reservations regarding the role of this test as a true predictor of MMCR success.³⁶ Although the majority of receptors in the Müller muscle are alpha-2 receptors,¹⁴,³⁶,³⁷ phenylephrine is a direct alpha-1 selective adrenergic agonist and not alpha-2 (the levator muscle predominantly shows β1 receptors).³⁷ Therefore, it seems plausible to suggest that the phenylephrine test is not as sensitive an indicator of the role of Müller muscle function as was previously thought, and a search for an alternative drug that more accurately and fully depicts muscle function is required.¹⁴,³⁶ Some patients with a negative response to the test may still benefit from MMCR. This is more commonly observed in older patients with long-standing ptosis and is attributed to degenerative changes in the Müller muscle which may cause atrophy of adrenergic receptors.¹²,¹³,¹⁴ Additionally, although MMCR is indicated primarily for mild to moderate ptosis, a certain percentage of patients with severely ptotic eyelids do respond well to phenylephrine testing and may benefit from MMCR. Therefore, the use of the test in clinical practice should not be restricted to milder cases and may be performed even in cases of severe aponeurotic ptosis.²³