Discussion

This case series provides a proof of concept that plication and stabilisation of the MCT to its desired position appear to be closely linked to the need for lower eyelid lengthening procedures, particularly in patients who have also undergone LTS, and/or those within the ‘contraction phase’ of FNP (ie, more than 1 year since onset). The authors, therefore, highlight the importance of preventing any unnecessary loss of horizontal tarsal length (particularly during LTS procedures) in patients with FNP, and of early identification of inadvertent eyelid shortening. In such cases, lengthening of the lower eyelid with a laterally based periosteal flap, hinged high on the lateral rim, improves outcomes of lower eyelid malposition in situations where the lateral edge of the tarsus cannot be distracted to reach the superolateral rim at an appropriate position. A useful indicator of lower eyelid shortening is that the lateral tarsal edge, at the lateral canthal angle, cannot be easily manually distracted to a higher superolateral position on the lateral orbital rim without signs of undue horizontal stretch and/or distraction of the lower punctum to the medial corneal limbus.

Anterior lamellar (skin and muscle) contraction is increasingly recognised in patients with FNP, with patients reaching a ‘contraction phase’ after variable periods since FNP onset, as early as 3 months.1 9 Skin contraction has been observed clinically in the context of FNP and previously described by us.1 Muscle stiffness is believed to be due to the formation of tight cross-bridges between actin and myosin which, it is hypothesised, are not sufficiently stretched by the impaired muscle contraction of patients with FNP to cause breakage of these bridges.9 Diminished activity can lead to local atrophy of muscle, bone and/or soft tissue (disuse atrophy). It has been suggested that impaired muscle pump function leads to reduced vascular tone and increased hydrostatic pressure within the soft tissues, leading to fibrosis of the subcutis and trophic skin changes.10

The position of the lower eyelid depends on the fine balance of a number of forces and interactions: gravity; tension and elasticity of the eyelid itself; the strength of its suspension (via the medial and lateral canthal tendons) and the eyelid’s relationship to both the globe and orbit.11 As we age, loss of tissue elasticity and subsequent elongation of the eyelid’s systems of support are counteracted by increased tone of the orbicularis oculi in order to maintain lower eyelid position. FNP, which causes a loss of orbicularis oculi innervation, is, therefore, more likely to cause its most severe lower eyelid sequelae (such as retraction, paralytic ectropion, lagophthalmos, epiphora and corneal exposure) in the elderly. Effective restoration of eyelid position—in a high position and well apposed to the globe—often requires a combination of reinforcing the MCT’s posterior attachments and fixation of the lateral tarsus high on the lateral orbital rim, in addition to release of inferior retractors, mid face support and even vertical lengthening of the anterior and middle lamellae (including skin grafting where skin contraction is evident).

Trans, or retro, caruncular approach MCT plication is one popular option adopted to help to correct medial lower eyelid ectropion and descent in patients with FNP.12–16 Posterior fixation of the medial tarsus helps elevate the medial eyelid vertically while maintaining its apposition to the globe, with care taken to ensure the lower punctum is not distracted too far medially. Medial elevation is particularly valuable given the loss of facial nerve innervation to the superficial pretarsal and preseptal orbicularis muscle fibres that insert on the anterior limb, as well as the thin posterior limb, of the MCT. The posterior limb of the MCT, which forms the anterior fascia of Horner’s pretarsal orbicularis muscle, inserts on the posterior lacrimal crest and, acting as a supporting band, directs forces generated by Horner’s muscle fibres in a superopostero-medial vector. These superoposterior MCT attachments, along with orbicularis muscle tone, help maintain the eyelids against the globe, and the puncta within the lacrimal lake. Lost integrity of the posterior limb (and attachments of the deep heads of the preseptal/pretarsal orbicularis muscles to the lacrimal sac fascia and medial orbital wall), in addition to the anterior limb and the superficial preseptal/pretarsal heads of the orbicularis muscles, contributes to medial lower eyelid descent that remains unaddressed with lateral eyelid tightening alone.12

The deep lateral canthal tendon attaches to Whitnall’s tubercule, just posterior to the lateral orbital rim, and plays a major role in the support of the lower eyelid. Efforts to repair and strengthen the lateral canthal tendon concentrated initially on the LTS procedure (first described by RL Anderson in 1979) and its variants.17 An alternative—a periosteal flap raised from the lateral orbital rim—was described in 1953 and suggested as a treatment of lower eyelid laxity and ectropion in 1988.18 19 This technique is particularly useful in the context of lower eyelid reconstruction, due to its ability to replace a deficit in posterior lamellar tissue.20 21 Other options to lengthen the lower eyelid posterior lamella do exist, however, including options such as tarsoconjunctival graft and free tarsal graft procedures.

In addition to lateral canthotomy, any operation that exposes the lateral lower eyelid (such as an LTS procedure) also involves inferior lateral cantholysis. Inferior cantholysis should be performed directly onto the orbital rim wherever possible to ensure that the eyelid length is not inadvertently iatrogenically shortened, which is of particular importance in patients within the contraction phase of FNP.

We have described seventeen cases in which patients with FNP have required lower eyelid lengthening (in the form of a lateral periosteal flap) in order to restore eyelid position and/or reattach the lateral tarsus, at or above the level of Whitnall’s tubercle. All of these patients had undergone plication of the MCT (either in the preceding years/months or the preceding minutes/seconds). A history of previous lower eyelid shortening procedures was present in eight (45%) of our cases requiring lower eyelid lengthening. In the first case described, the patient had undergone four procedures that would have shortened the length of the lower eyelid (MCT plication x2, LTS x2), and it might have been expected that a lid-lengthening procedure would have been required. However, in four cases (cases 7, 10, 12 and 13), the patients were surgery-naïve. Other factors that may increase the risk of requiring lower eyelid lengthening are patients within the ‘contraction phase’ of FNP (n=16/17, 94%), and those with fair skin (n=13/17, 76%), who the authors hypothesise are more prone to lower lid shortening due to their propensity for cicatrisation.

We suggest that plication (literally, folding) of the stretched MCT draws the lower eyelid to a more medial position than seen in the normal eyelid (figure 3). This creates a pseudo-shortening of the eyelid, the effect of which may be augmented by LTS procedures, which cause a true shortening of the eyelid. Patients undergoing LTS will have sections of the tarsal plate resected. With more than one LTS procedure, this leads to significant horizontal shortage of the tarsus, further contributing to the problem. The authors suggest that when performing an LTS procedure, a minimum of tarsus should be excised. In addition, the lateral position of reattachment should be higher than Whitnall’s tubercle. The tarsal plate does not physiologically attach directly to the lateral orbital rim. When surgically placing the tarsal plate to the lateral orbital rim, particularly on tension, a pseudo-tendonous scar will form between tarsal edge and rim, resulting in subsequent descent of the lower eyelid and lateral canthal angle over time.

Two outcomes of lower eyelid shortening are seen in this series: (1) lower eyelid retraction and/or ectropion due to increased horizontal tension and (2) failure to reattach the lateral tarsus to the lateral orbital rim in cases where MCT plication is performed, as is often the case, in combination with lateral canthotomy/lateral canthoplasty. Elongation of the horizontal eyelid margin posterior lamella enables reattachment of the lower lid to the lateral orbital rim, ideally above the level of Whitnall’s tubercle and restoration of a more natural superotemporal vector to the lateral eyelid margin. This can be achieved by creating a lateral periosteal flap.

Limitations of this series include the heterogenous nature of our cohort. FNP patients are complex patients, managed with a wide variety of surgical and non-surgical procedures and techniques, and so comparison of these cases is inherently difficult. While recession of lower eyelid retractors will also improve lower eyelid elevation, it would be unethical to simply perform horizontal eyelid lengthening while ignoring the impact of vertical factors such as the lower eyelid retractors in any study. Therefore, it is unlikely that any case-controlled prospective study evaluating the sole benefit of horizontal lengthening will ever be possible. Furthermore, in each case within this series, lower eyelid retractor recession and lysis of medial and lateral horns were performed prior to deciding if a lateral periosteal flap was essential. It was evident that horizontal eyelid lengthening was required despite release and recession of lower eyelid retractors, providing further proof that this is of additional benefit.

Our series highlights that the need for lower eyelid lengthening is closely linked to MCT plication having been performed. We emphasise that in all cases, the end-point of MCT plication was that the lower punctum was placed just medial to the medial limbus, avoiding excessive medial distraction of the punctum towards the plica by applying less tension through the plicating suture. However, we recognise that it is possible that overenthusiastic MCT plication would obviously shorten the horizontal eyelid further, and this may be an obvious concern when deciding if a periosteal flap is necessary.

Anterior lamellar contraction may well have contributed to the lower eyelid shortening seen in this case series, although its role is likely to be limited for two reasons. First, in all cases, satisfactory lid lengthening was achieved without the need for a skin graft to augment the anterior lamella. Second, in case 8, eyelid shortening was noticed intraoperatively only 5 months after the onset of FNP—possibly too early for a significant degree of anterior lamellar contraction to have occurred. It is difficult to quantify lower eyelid skin contraction due to the lack of defined landmarks. We record upper eyelid margin-to-brow (LMBD) in all cases at each visit in our service. The method is described in detail in a previous publication.1 We have previously shown this to be a useful indicator of upper eyelid skin contraction and is, therefore, a potential indicator of the possible presence of lower eyelid skin contraction. We would encourage this measurement be taken in all patients with FNP. While the observation that a periosteal flap is most likely to be required after previous iatrogenic eyelid shortening may be logical to accept, our second observation that patients in the contraction phase of FNP may also need horizontal eyelid lengthening requires readers to recognise the contraction phase in FNP by way of indirect measurements such as the upper eyelid LMBD on each side. This an indirect sign of periorbital contraction. This may help alert the clinician to not only avoid further horizontal eyelid shortening but to also consider the possible need for eyelid lengthening with a periosteal flap, alongside the possible need for skin grafting.

This case series describes 17 patients with FNP who required lower eyelid lengthening, in the form of a lateral periosteal flap—in each case, following MCT plication (either performed within the same operation or during a previous one). This situation also appears to be closely associated with previous lid-shortening procedures (eg, LTS), and/or those within the ‘contraction phase’ of FNP. The authors, therefore, highlight the importance of preventing any unnecessary loss of horizontal tarsal length (particularly during LTS procedures) in patients with FNP. It is also important to note that due to the changing dynamics of the lower eyelid following the onset of FNP, effective surgery in the first 6 months since onset may be different from that required once the contraction phase has been reached. Surgeons managing such patients should take care to identify inadvertent eyelid shortening early. A useful indicator of lower eyelid shortening is that the lateral tarsal edge, at the lateral canthal angle, cannot be easily manually distracted to a higher superolateral position on the lateral orbital rim without signs of undue horizontal stretch and/or distraction of the lower punctum to the medial corneal limbus. The authors suggest that lower eyelid lengthening with a laterally based periosteal flap, hinged high on the lateral rim, will improve the outcomes of lower eyelid malposition surgery in such cases.