A review of surgical management of progressive myogenic ptosis

ABSTRACT Purpose Surgical correction of myogenic ptosis is a sophisticated endeavor, as the disease is progressive and the post-operative course is prone to significant complications. We sought to review the literature for repair techniques in different types of myogenic ptosis. Methods A PubMed/MEDLINE literature search of publications pertaining to surgical outcomes of progressive myogenic ptosis repair was performed. Studies included were original retrospective studies with a minimum of four patients. Results A total of 27 articles were identified and divided by etiology of myogenic ptosis; either chronic progressive external ophthalmoplegia (CPEO), oculopharyngeal muscular dystrophy (OPMD), myasthenia gravis (MG), or mixed. Surgical techniques predominantly involved levator advancement, levator resection, frontalis sling, blepharoplasty, and Fasanella-Servat. Success rates ranged from 60.5% to 100%. Significant postoperative complications included ptosis recurrence, under-correction, over-correction, keratopathy, lagophthalmos, sling exposure, and sling infection. Conclusion Like surgical repair for other forms of ptosis, correction of progressive myogenic ptosis is guided by levator excursion. However, myogenic ptosis is especially challenging as it is characterized by worsening ptosis and the loss of protective corneal mechanisms. The goals of care with myogenic ptosis involves repairing ptosis just sufficiently to alleviate visual obstruction while avoiding adverse post-operative complications. This intentional under-correction subsequently increases susceptibility for ptosis recurrence. Myogenic ptosis repair therefore requires delicate balancing between function, sustained repair, and corneal protection.


Introduction
Myogenic ptosis encompasses a family of myopathies, dystrophies, and syndromes that are known to particularly affect the extraocular muscles, among other muscles of the face and body. These disease entities are relatively rare and include mitochondrial myopathies such as chronic progressive external ophthalmoplegia (CPEO) and Kearns-Sayre syndrome (KSS), oculopharyngeal muscular dystrophy (OPMD), oculopharyngeal distal myopathy (ODM), and myotonic dystrophy (MD). 1 Surgical correction of myopathic ptosis in affected individuals is typically reserved for symptomatic cases where the upper lid obstructs the visual axis. 2 Repair is often challenging, as myogenic ptosis not only affects the levator, but also the other extraocular, orbicularis, and in some cases, the frontalis muscles. 3 Additionally, many patients have pre-existing dry eye due to a poor blink reflex and tear secretion, necessitating caution to avoid postoperative corneal complications. 4 Several of these pathologies are progressive, with worsening ptosis or an increasing risk of recurrence over time after repair. 4 Given this complexity, several studies in the literature have detailed their own surgical experiences, techniques, and outcomes. However, to our knowledge, there has been no recent comprehensive review of the surgical outcomes of progressive myogenic ptosis repair. In this report, the authors review literature focusing on the results of both classic and innovative repair techniques in different types of myogenic ptosis. Our PubMed/MEDLINE search generated 238 search results, of which 60 non-English results and 6 lab/animal studies were excluded. Titles and abstracts were screened in the remaining 172 articles for relevance to surgical outcomes of myogenic ptosis. Original prospective and retrospective studies were included in the analysis. Case series with three or fewer patients were excluded. Relevant references from systematic reviews and meta-analyses were evaluated, but studies not containing original data were also excluded. A total of 116 articles were excluded at this stage: 35 were nonmyogenic ptosis related, 58 were non-surgical, and 23 were case reports or reviews. The remaining 56 papers then underwent full-text screening: 12 did not involve a surgical prospective or retrospective review, 7 had no relevant surgical outcomes measured, and 10 lacked a patient cohort predominantly involving myogenic ptosis. A total of 27 articles were finally included for assessment and review. 1,3,5-29

Results
All data involving etiology of ptosis, number of patients and lids, surgical technique, surgical criteria, primary outcomes, success rates, significant complications, and follow-up time across the 27 articles reviewed have been detailed in Table S1. For this review, when a success rate for a study was not explicitly reported, it was calculated based on the number of patients or the number of lids that had not necessitated secondary surgery for recurrence, a significant post-operative complication, or over-/under-correction. Additionally, significant complications were defined as adverse postoperative events requiring intervention beyond conservative medical management.
Five pre-post case series (51 patients and 97 eyelids) investigating the surgical outcomes of various ptosis repair procedures for CPEO were reviewed. Techniques included anterior approach levator advancement (LA), levator resection (LR), and frontalis suspension (FS) sling with various materials. Overall, frontalis suspension was the most performed surgical procedure in this population (70%, n = 68 of 97 lids). Aggregate success rate of ptosis repair, defined as successful elevation with one procedure, across all five CPEO studies was 95.9% (93/97 lids). Significant complications from each of the studies ranged from 0% to 10% and involved asymmetry (1), corneal ulcer (1), corneal abscess (1), and corneal exposure (2) ( Table 1).
Across six case studies (328 patients and 652 eyelids) investigating the surgical correction of OPMD ptosis, levator modification (advancement or resection) was performed on 34% of eyelids (n = 196 of 580), frontalis suspension was on 61% of eyelids (n = 354 of 580), and blepharoplasty on 5.2% of eyelids (n = 30 of 580) when specified. Aggregate success rate was 80% (n = 523 of 652 lids). Significant complications from each of these studies ranged from 3% to 25% and involved recurrence, under-correction, and over-correction (Table 1).
In total, four pre-post and two retrospective comparative studies involving 79 patients and 125 eyelids in myasthenia gravis were reviewed. Nearly all patients had failed a trial of medical therapy prior to undergoing surgical intervention. Overall the aggregate success rate, defined by ptosis repair requiring only one procedure, was 85.6% (n = 107 of 125 eyelids). Ptosis repair techniques were varied: LA (43%), frontalis suspension (39%), posterior approach (14%), blepharoplasty, and tarsal switch (TS) were all reported. Significant complications ranged from 0% to 39.5% and involved recurrence, under-correction, keratopathy, lagophthalmos, and diplopia (Table 1).

Levator function dictates type of procedure
Levator function was frequently used to guide choice of surgery for CPEO-associated blepharoptosis correction, as demonstrated first by Lane and Collin who adapted Beard's surgical guidelines. 5, 30 Lane and Collin performed levator advancement (LA) on seven patients with levator function >4 mm and a fascia lata frontalis suspension (FS) on eight patients with levator function <4 mm. 5 They reported satisfactory results in 93% of all lids (n = 25 of 27). 5 Eshaghi et al. used the same criterion for levator resection (16 lids) versus frontalis suspension with silicone (8 lids), producing significant postoperative improvements in margin reflex distance 1 (ΔMRD 1 = 2.96 mm) and chin-up posture (−18.3° chin-up angle) at 1-year follow-up in all patients (100%, n = 24 lids). 9 There were no reoperations, recurrences, or significant complications. , with both studies producing successful elevation (ΔMRD 1 = 2.7 in both studies) in all patients. 7,8 Levator function was also the primary factor in selecting surgical procedure for OPMD. However, unlike the CPEO studies, the LF thresholds used in these six studies varied widely from one another. Generally, FS was performed in patients with poor LF, whereas levator advancement or resection was performed in patients with good LF. Johnson et al. utilized LR for patients with good LF >9 mm, and FS for patients with LF <9 mm. 10 The authors reasoned that the progressive nature of OPMD would worsen the levator muscle further with time, increasing the susceptibility to ptosis recurrence, and hence necessitating a higher threshold for resecting the levator muscle. The results were 97% satisfactory with only one patient requiring reoperation with fascia sling due to ptosis recurrence. By contrast, Rodrigue et al. performed LR for all patients with LF >4 mm, reserving FS only for cases of severe LF <4 mm. 11 They assert that OPMD, unlike CPEO, rarely causes ophthalmoplegia, thereby permitting reliable application of Beard's guidelines. 31 Thus, the majority of their study's patients (96% of lids) received bilateral LR. Satisfactory outcome was achieved in 96% of patients with 0% recurrence at 9 years of follow-up and 13% recurrence beyond that. 11 Like Johnson et al., Allen et al. used a higher LF threshold of 10 mm in their selection of levator advancement in 68 patients. 12 However, they also incorporated age of onset of ptosis into their algorithm, with younger age discouraging levator advancement. Frontalis suspension was performed in patients with LF <10 mm or in patients with LF >10 mm and ptosis onset before age 60 (61%, n = 102 of 166 lids). Otherwise, levator advancement was performed in patients with LF >10 mm with onset after age 60. Successful elevation was found in 62.7% of patients, with a recurrence rate of 47.1% among those who received levator advancement, 7.8% with frontalis suspension, and 93% with blepharoplasty. In a deviation from this pattern of levator resection for "good" LF, Kang et al. performed LR on four patients from a family afflicted by OPMD. 3 All patients had LF <8 mm, which by some surgical guidelines would warrant frontalis suspension, but because all frontalis functions were significantly impaired in this family, they were precluded from any sort of frontalis suspension procedure. Success rate was 87.5% (n = 7 of 8 lids) with one lid requiring revision for recurrent ptosis. Although decreased frontalis function is atypical in this myopathy, these surgical experiences highlight that ptosis repair selection based exclusively on LF can be misguided.
Most of the six case series reviewed on ptosis repair in myasthenia gravis did not specify a levator function threshold to guide selection of surgical technique. For example, Bradley et al. did not explain the rationale behind choosing ELA versus frontalis suspension for their 10 patients, but mean preoperative LF for ELA patients was 12 mm. 28 There was no data on preoperative LF in the frontalis suspension group. Satisfactory ptosis correction was achieved in 75% of lids (n = 12 of 16) with one procedure. Two lids from the ELA group (22%) required re-operation for recurrence, and two lids from the FS group (33%) required sling release for postoperative lagophthalmos. Likewise, Brogan et al. performed ELA on 11 patients (16 eyelids) with preop LF ranging from 10 to 15 mm. 19 Satisfactory ptosis correction was achieved in 93% of lids (n = 13 of 14), with one lid (6%) requiring re-operation for recurrence.
In the MG papers that did dictate surgical guidelines, the general pattern of utilizing ELA in cases of good LF and FS in cases of poor or expected-to-be poor LF emerged. Shimizu and colleagues treated 11 eyelids with myasthenic blepharoptosis, taking into account LF, MRD 1 , and skin thickness/redundancy 15 ; If LF <4 mm or LF >4 mm with an expected decrease over time, FS was performed. If LF >4 mm and MRD <2 mm, ELA was performed. If LF >4 mm and MRD >2 mm with concomitant skin redundancy, a subbrow blepharoplasty (SBB) was performed. MRD 1 increased the most after FS (average increase 4.1 mm), compared to ELA (average increase 1.3 mm) and SBB (average 0 mm increase). Although subbrow blepharoplasty with orbicularis oculi muscle tucking has no direct involvement of the levator or frontalis muscles, it was employed in patients with thick eyelid skin to reduce lateral hooding, decrease the weight on the upper lid, and elevate the lid margin. 15 All patients in this study expressed satisfaction, including the patient who received a SBB, and no serious postoperative complications were noted. Lai et al. performed a variation of FS using a frontalis orbicularis oculi muscle (FOOM) flap in 12 patients (24 lids) with an average pre-op LF of 12 mm. 18 Despite moderate levator function, the decision was made by the authors not to proceed with a levator-based procedure due to the variable changes to the muscle seen in the OMG disease course. No serious complications or recurrences were noted.
A study of 24 eyelids conducted by Buttanri and colleagues for unspecified myopathic ptosis demonstrated that levator resection had improved success rates with higher pre-operative LF. 25 Aggregate success across all 12 patients (n = 24 lids) was 70.8%. When the pre-operative LF was 4-5 mm (n = 7 lids), the success rate of levator resection was 42.8%. At LF 6-7 mm (n = 7 lids) it increased to 71.4%, at 8-9 mm (n = 6 lids), it improved further to 83.3%, and at 10-12 mm (n = 4 lids), it reached 100%. These results validate that LR should be reserved for use in patients with intact LF, a concept consistently described and adopted by many of the authors in the studies reviewed.

Frontalis sling techniques and efficacy
Each of the five CPEO studies reviewed did not directly compare different frontalis sling materials (fascia vs. silicone vs. nylon) within their respective studies. Instead, each produced strong rationale and results advocating for its particular material choice. Both Sebastia et al. and Lane and Collin used autologous or stored fascia slings, with Lane and Collin highlighting the decreased risk of infection, relative to foreign material. 5 However, no cases of sling infection (0%) were noted in any of the CPEO case series reviewed, across all sling materials. Eshaghi et al. and Ahn et al. utilized silicone slings, with Ahn et al. drawing attention to their elasticity, resulting in relatively improved adjustability and accurate eyelid approximation, and thereby theoretically reducing risk of lagophthalmos and postoperative corneal exposure. 7 No significant corneal pathology was noted in either silicone sling study and the post-operative increases in lid lag and lagophthalmos were not significant. 9 By contrast, more serious corneal complications were noted in patients who received fascia slings. Two lids (14%) in Lane et al.'s FS cohort experienced marked corneal exposure requiring fascial bands to be cut. 5 One lid (7%) in Sebastia et al.'s FS cohort developed severe exposure keratitis with corneal ulcer and leukoma despite aggressive lubrication. 8 A less commonly discussed sling material, monofilament nylon, was studied by Shorr et al. in 10 patients because of its availability, ease of use, and simple removal. 6 Corneal sequelae were minimal with this material; the only complication involved under-correction in one lid (5%) requiring reoperation. The CPEO case series reviewed did not examine the use of monofilament polypropylene suture as a sling material. However, multiple studies, though not exclusively in myogenic etiologies of ptosis, have demonstrated its success in pediatric and adult age groups. Polypropylene is available, economical, easy to remove or adjust, and its relative thickness offers a high tensile strength that has been shown to last for years. 32,33 In very young children, even as young as 1 month of age, polypropylene frontalis suspension provides sustained ptosis correction for deferral of autogenous fascial lata suspension. 33 Overall, silicone and fascia were commonly used in the CPEO studies reviewed, with silicone offering greater corneal protection and only a theoretically increased risk of sling infection.
A direct comparison study of two specific frontalis suspension techniques with propylene slings (trapezoid vs. modified Crawford) performed by Kalin-Hadju and colleagues depicts the efficacy of frontalis slings in OPMD. 14 13 There were no instances of sling infection, extrusion, or corneal complications. Patient satisfaction was not reported, but only six patients (19%) underwent early revision and three patients (10%) underwent late tightening of slings, likely secondary to loosening of the sling, increasing weakness of the residual levator function, and/or stretch of the silicone material over time.
The success of frontalis suspension in CPEO, OPMD, and MG has been previously emphasized.  21,24,26,27 Success rates of frontalis suspension among these five studies ranged from 78.6% to 100%. Significant complications, which were relatively rare, involved corneal ulceration (<7%), under-correction /over-correction (<7%), sling infection (< 6.25%), and sling exposure (< 7%). Studies by Lelli et al. and Sorge et al. also involved frontalis suspension, but their patient populations included both myogenic and neurogenic ptosis type. 22,23 Lelli and colleagues determined through a Kaplan-Meier survival analysis of time to decision for adjustment, that among MG, CPEO, OPMD, and CN3 palsy, MG had the longest survival, followed by CPEO. These results indicate that differing recurrence rates and complications may not only be secondary to technique or sling material, but also involve disease entity and course.

Unique considerations
Certain authors caution against surgical overcorrection in myasthenic ptosis. MG patients can often demonstrate a good levator function even with severe ptosis, predisposing them to intraoperative overcorrection and postoperative lagophthalmos. Thus, surgery should aim to cautiously lift the eyelid while avoiding preventable corneal exposure, achieved through under-correction. 16 Recurrent reoperations should be expected in the conservative surgical approach described by these authors.
Litwin et al. analyzed 38 blepharoptosis procedures, involving levator advancement (anterior and posterior approaches), frontalis suspension, and tarsal switch, performed on 23 patients with MG. 16 Only one lid of one patient (2.6%) required lid lowering due to keratopathy. However, 14 eyelids (37%) required upper eyelid height revision due to under-correction. The authors do not specify surgical parameters that guided this intentional under-correction. Instead, they compare their increased rate of under-correction with the rate of an earlier MG case series by Bradley et al. (37% vs. 12.5%) to demonstrate the shift toward "less ambitious gains in eyelid height in favor of functional results with a preference to repeat surgery." 16 Similarly, Belliveau et al. examined 13 patients (n = 20 lids) who underwent surgery via Fasanella-Servat or LA, 17 with a conservative lid elevation goal of 2.0 mm (average ΔMRD 1 ). 17 Three lids (15%) required repeat repair due to recurrence over a 9-month follow-up period. No serious corneal complications were noted.
Doherty et al. introduced elevation of the lower lid prophylactically in 10 lids of patients with lagophthalmos, prior to ptosis surgery for unspecified myopathic ptosis. 24 This was part of a novel surgical approach to minimize corneal complications post-operatively, by adjusting otherwise normal lower lids. Although the authors do not specify the results of this sub-set of patients who received surgical prophylaxis, the overall success rate was 88.3% (53/60 lids) and the complication rate was 13.3% (8/60 lids) with two lids experiencing corneal ulceration.
Lu et al. performed frontalis suspension with an "under-corrected double V-loop" on six patients (n = 12 lids) with CPEO or MG as part of a surgical strategy to avoid keratopathy. 27 This involved suspending the frontalis muscle with a suture such that the upper lid margin was placed just at the upper edge of the pupil. PF and MRD both increased by 1.75 mm. While the authors concede that this poses a greater risk of ptosis recurrence, no recurrence was noted despite their intentional under-correction. As theorized, there was also no serious corneal complications.
Burnstine and Putterman described the favorable results achieved with upper blepharoplasty alone in six patients with unspecified myopathic ptosis. 20 MRD 1 improved by an average of 3.25 mm. Five patients (83.3%) experienced successful resolution with repair, with one requiring re-operation due to persistent ptosis. Vemuri and colleagues advocate for the "Bobby Pin Procedure," a simple, effective (92.3%), long-lasting (7.7% recurrence) variant of a pinch blepharoplasty that overcorrects without causing symptomatic lagophthalmos. 29 Among 26 lids (OPMD, CPEO, MD, idiopathic), post-operative PF improved by 0.89 mm and MRD by 1.5 mm. Aside from one patient experiencing ptosis recurrence, no other significant complications were noted. Despite the popularity and the strength of evidence reinforcing frontalis suspension as a robust option for myogenic ptosis repair, other techniques and variations continue to demonstrate promise.

Discussion
Chronic progressive external ophthalmoplegia (CPEO) represents a group of neuromyopathic disorders with features of progressive bilateral ptosis and symmetric deficits in ocular motility. 34 CPEO can occur in isolation (Isolated CPEO) or as part of a systemic disease entity with more widespread manifestations (CPEO plus). 35 The disease is thought to be the result of genetic mutations associated with mitochondrial dysfunction and defective oxidative phosphorylation. 36 Symptoms can present at any age, 37 but typically begin by the third decade of life. 9 The orbicularis oculi, levator palpebrae superioris, and extraocular muscles are preferentially affected, leading to ophthalmic findings of progressively worsening bilateral ptosis and symmetric ophthalmoparesis. 34 This worsening ptosis will often force patients to compensate by adopting a chin-up head position ("backward head tilt"), 7 and is usually the symptom that brings patients to seek care. 34 By contrast, frontalis muscle function remains relatively preserved, and deep forehead furrows may be visible due to constant contraction to raise the lids. 6 Oculopharyngeal muscular dystrophy (OPMD) is a slowly progressive disease involving symmetric blepharoptosis, dysphagia, and proximal muscle weakness. 3 It is inherited in an autosomal dominant pattern and its onset is insidious, typically manifesting during the fifth or sixth decade of life. 3 French Canadians (Quebec), Hispanic New Mexicans, and Israeli Bukhara Jewish populations are most prevalently affected by OPMD. 13 The condition is diagnosed through molecular genetic testing and manifests as a myopathy affecting skeletal muscle cells. 38 The levator palpebrae superioris and pharyngeal muscles are often most severely impaired, but the disease can also involve other extraocular muscles and limb muscle groups. 38 Patients will compensate for progression of ptosis with contraction of the frontalis muscle and "backward head tilt." 38 Meanwhile, the orbicularis oculi muscle and Bell's phenomenon are fairly well-preserved in OPMD patients. 3 Surgical techniques described include blepharoplasty, levator advancement, frontalis sling, and combined aponeurosis-Muller muscle advancement. 12 Ocular myasthenia gravis (OMG) is a form of myasthenia gravis (MG) localized to muscles of the eye. Like its systemic counterpart, OMG is caused by antibodies directed against acetylcholine receptors (AChR) at the skeletal muscle postsynaptic neuromuscular junction. 39 Typically, the levator palpebrae superioris (unilaterally or bilaterally), extraocular muscles (most commonly the medial rectus), and orbicularis oculi muscle (OOM) (commonly bilateral) are affected. 40 OMG patients will classically present with fatigable ptosis and/or diplopia in the absence of other ocular or systemic symptoms. 39 Positive physical exam signs include enhancement of ptosis with passive elevation of the contralateral lid, fatigable ptosis, pseudoretraction of the contralateral unaffected lid, the "peek sign" in which sustained forceful eye closure induces OOM fatigue and eventually scleral show, and Cogan's lid twitch. 39,40 OMG is a clinical diagnosis, although serum AChR antibody testing, electrophysiology, and pharmacologic tests are supportive findings. 39 Treatment of OMG ptosis and diplopia can be managed first with patching, spectacle lid crutches, and taping. Medical treatment with cholinesterase inhibitors, corticosteroids, and/or non-steroid immunosuppressants can be considered. If refractory to conservative and/or pharmacologic treatment, surgical intervention for ptosis correction can be pursued.
Though CPEO, OPMD, MG, and other myotonic dystrophies encompass unique disease entities, the risk profile and complexities of ptosis repair remain largely the same. Prudent management of ptosis can be challenging as the provider must reconcile the efficacy of surgical correction of ptosis with the very real risks of postoperative exposure keratopathy, abnormal cosmesis, and ptosis recurrence with disease progression. 7,9,34,41 Exposure keratopathy following surgical ptosis correction has been well-documented and is believed to be due to the combination of surgically increased palpebral fissure (PF) height, pathologic weakness of the superior rectus (impaired Bell's phenomenon) and orbicularis oculi (incomplete blink response) muscles, and preexisting concomitant dry eye. 9,34 Surgical management of ptosis is therefore typically reserved for obstruction of the visual axis. 2 This literature review sought to elucidate surgical guidelines by analyzing postoperative outcomes in myopathic ptosis repair. Of the five pre-post case series reviewed regarding repair of CPEO ptosis, the aggregate success rate was 95.9% (n = 97 lids). By contrast, the six case series on OPMD exhibited an aggregate success rate of 80% (n = 652 lids), and the six case series on MG ptosis had a success rate of 86% (n = 125 lids). In general, LF below a specific threshold warranted frontalis suspension. Lids with LF above this threshold frequently underwent levator modification. For the management of CPEO ptosis, the LF threshold was most commonly around 4 mm. 5,[7][8][9] For OPMD, the threshold varied, with some authors performing frontalis suspension only if LF <12 mm. 14 Some authors additionally incorporated pre-operative MRD 1 or age of onset into their surgical criterion, with later onset trending towards levator advancement due to the decreased likelihood of ptosis progression or recurrence. 12,14,21,25 However, these additional parameters were not implemented with enough frequency to draw any conclusions about the efficacy of this approach compared to measuring levator function alone.
Post-operative outcomes such as ΔPF and ΔMRD exhibited a general trend of increased improvement with frontalis slings than with levator modification procedures. However, it is important to note in the interpretation of our data that the goals of myogenic ptosis repair differ from those in other forms of ptosis. With myogenic ptosis, several authors have explicitly described intentional under-correction, repairing ptosis just adequately to alleviate visual obstruction while avoiding adverse post-operative complications. 16,17 This guarded approach has understandable downstream effects on outcome measures such as ΔPF and ΔMRD, rendering it difficult to compare these results with those of other non-myogenic ptosis studies.
Frontalis suspension with a variety of different sling materials, most commonly silicone and fascia, was utilized predominately in patients with CPEO (70%) and OPMD (61%). Levator advancement (43%) was the primary technique in MG ptosis, followed closely by frontalis suspension (39%).
Significant corneal complications were relatively limited as many providers prescribed prophylactic lubrication immediately following surgery or initiated an aggressive regimen at the first signs of keratopathy. Much of the preoperative planning and choice of procedure was guided by restoring function while avoiding undue harm. When significant complications did occur, they included corneal desiccation, abscess, and ulcers.
Notably, a pediatric case series has demonstrated the possibility of adult-onset exposure keratitis decades after childhood ptosis repair with frontalis slings. 42 This is a late complication to consider, especially in the surgical planning of congenital ptoses. In select cases where exposure keratitis can be predicted based on suboptimal existing corneal protective mechanisms, the lower eyelid can be prophylactically elevated prior to or at the same time as upper eyelid ptosis repair by releasing the lower eyelid retractors and using a spacer graft. 43,44 Sling exposure (7%), infection (6%), or rejection in frontalis suspensions were overall rare despite the increased theoretical risk with insertion of foreign material. 1, 24 Rates of recurrence, under-correction, and overcorrection were quite variable among the studies; need for revisional surgery ranged up to 39% as it was the most common complication. 22 This wide spectrum can be explained by multiple factors. In disease entities involving myogenic ptosis, the clinical course is often characterized by gradually worsening ptosis as the disease progresses. As a result, we would expect re-operation rates for myogenic ptosis to be higher compared to most other forms of ptosis. Secondly, there was an intentional effort to undercorrect ptosis by some authors in this study, as part of a conservative approach to decrease incidence of corneal complications and over-correction. 16,17 Lastly, differing rates of re-operation can also be attributed to the age of patients at time of surgery and the duration of follow-up (range 0-192 months), as explained further below.

Limitations
There are several limitations in this systematic review. Data has been drawn exclusively from published articles, contributing to a publication bias. Myogenic ptosis is an expansive subject matter inclusive of many progressive myopathies that are not uniformly represented in the literature and in this review, rendering our results less generalizable. Many of our findings, therefore, pertained to surgical management of progressive myogenic ptoses and were less inclusive of static or congenital ptoses. 45 Additionally, the articles involved are predominantly noncomparative, interventional case series, which decreases our ability to qualify the impact of one intervention over another as the studies are not controlled. Among the 27 studies reviewed, there is also inherent heterogeneity of the studies in terms of patient population, methodology, surgical technique, primary outcomes, and follow-up. For example, some studies had a follow-up time that spanned years while others lasted only a few months (range 0-192 months). This variation makes it difficult to directly compare studies and draw meaningful, definitive conclusions regarding analysis among myogenic ptosis etiologies. It also undoubtedly confounds success rates and data regarding complications and revisions, as both are likely to increase over time. Furthermore, articles were particularly variable in which data points they explored and selectively reported. For example, it was not always clarified whether patients had prior ptosis repair. It was also not always clear how authors came to define surgical success as some studies interpreted it as clearing of the visual axis, others as requiring only one procedure, and still others as patient satisfaction. As mentioned previously, success rates for several of these studies were not reported and had to be calculated based on their complication and recurrence rates. This is a potential limitation since endpoint outcomes and measurements were not standardized pre-or post-operatively. Lastly, there is evolving discourse regarding the accuracy and quality of using eyelid excursion measurements as an indicator of levator function. 13,14,46 Its validity as a reflection of levator strength and use as a surgical parameter warrants further research.

Conclusion
The repair of myogenic ptosis is a challenging and, at times, controversial issue. Traditionally, measurement of levator function governs the type of ptosis repair, most commonly frontalis suspension for diminished levator function and levator modification for intact muscle function. Successful elevation of the upper lid is dependent on an assortment of factors, primarily but not limited to etiology, existing muscle function, severity of ptosis, and surgical technique. Ultimately, the severity of ptosis, existing levator function, and presence of corneal protective mechanisms should be a starting point for guiding surgical management of myogenic ptosis. With all surgical techniques and ptosis disease entities, caution is paramount to avoid corneal complications, lid lag, lagophthalmos, under-correction, over-correction, and recurrence. Myopathic ptosis repair therefore represents an intricate and sophisticated balancing act between cosmesis, visual function, sustained repair, and corneal protection.

Disclosure statement
Dr. Vinay K. Aakalu: Patents owned by the Board of Trustees of the University of Illinois and equity ownership ViSo Therapeutics Inc. These do not pertain to the subject matter reported in this article.

Funding
This work was supported by The National Institutes of Health, National Eye Institute under Grant [P30EY001792] and by