Ординатура / Офтальмология / Английские материалы / Atlas of Aesthetic Eyelid and Periocular Surgery_Spinelli, Lewis, Elahi_2004

The lateral canthal tendon should be a most familiar structure to the surgeon and is more commonly addressed than the medial canthal complex. It should be thought of as contiguous with the tarsal plates and measures approximately 2 mm in width and 6 mm in length. It is a rather thin structure that splits into an anterior and posterior leaflet, with the anterior being contiguous with the orbital rim periosteum and the posterior element inserting on the lateral orbital tubercle (Whitnall’s), approximately 3 mm behind the orbital rim. This structure lies approximately 6 mm below the lacrimal gland fossa. Superficial and deep components of the orbicularis oculi muscle (both preseptal and pretarsal) accompany the superficial and deep layers of the lateral canthal tendinous complex. The lateral horn of the levator aponeurosis, which splits the lacrimal gland into orbital and palpebral lobes, also inserts on Whitnall’s tubercle, blending with the insertion of the lateral canthal tendon. Therefore, Whitnall’s tubercle is analogous to the lacrimal fossae in that there is a convergence of support and suspensory structures that coalesce as anchor points for the eyelids, which otherwise are “floating in space” (Fig. 1-15). The

lateral canthal tendon complex or lateral retinaculum additionally contains a coalescence of the inferior suspensory ligament of Lockwood and the check ligament of the lateral rectus muscle. It is also firmly adherent to the orbital septum and lateral orbital periosteum, which is definitively thickened in this region. From a clinical perspective one key anatomic point is that division of the lateral canthal tendon in and of itself is not sufficient to mobilize the lateral canthal tendon complex or lateral retinaculum and, hence, lower and/or upper eyelid mobility and transposition can only be achieved with division of additional structures in the lateral canthal tendon complex. Failure to address all key elements of the lateral retinaculum will result in an inability to mobilize the lateral canthus in repositioning and/or tightening procedures. Typically, this is illustrated when “lateral canthopexies” do not achieve lower eyelid or lateral canthal elevation or suspension and tightening. Topographically, the lateral canthal tendon should be inclined 10 to 15 degrees when compared with the medial canthal tendon, and it is this position that is anatomic, physiologic, and most aesthetically pleasing.

ORBITAL FAT

Orbital fat is generally the focus of much of the cosmetic surgery in the periocular region. Whether resection, repositioning, or a combination of both is chosen for an individual patient, some fundamental anatomic points are helpful. First, all fat lies behind the orbital septum, which is contiguous with the periosteum of the bone surrounding the orbit. Here the orbital septum serves as a boundary against infection and tumor spread and basically prevents contiguous access from the anterior tissue planes to the deeper orbit where vital structures transgress bony apertures into the anterior and middle cranial fossae. In the upper lid all fat that is to be addressed is anterior to the levator aponeurosis and, hence, is termed preaponeurotic. Analogously, all postseptal fat in the lower eyelid is in the precapsulopalpebral fascial plane (see Fig. 1-2B). All fat accessed through the orbital septum is contiguous with the entire extraconal (outside the muscle cone) and intraconal (within the muscle cone) spaces (see Fig. 1-8B). Therefore, traction on fat just posterior to the orbital septum can produce forces in the posterior extraconal and even posterior intraconal and perioptic nerve region (see Fig. 1-8). The linkage of fat within the orbit by way of septa that transgress the extraocular muscle cone is the reason why there is a small but definitive risk of orbital hemorrhage and even blindness when addressing anterior orbital fat in surgical procedures. These interconnecting septa are also the reason why orbital hemorrhages do not spontaneously decompress with opening the orbital septum. Blood is generally trapped within the intraconal and extraconal spaces by this fascial network, and “indirect” decompression requires division of the inferior crus of the lateral canthal tendon and sometimes decompression of the anterior chamber of the eye, along with medical therapy such as corticosteroids, acetazolamide, and mannitol. I

use the term indirect because the decompression is only aimed at decreasing intraocular pressure and not at evacuation of intraorbital blood.

THE LACRIMAL APPARATUS

The lacrimal apparatus consists of structures that produce, distribute, and drain tears. The tear film is extremely important because it provides a wetting surface for gliding of the eyelids and eyeball structures against one another. Tears are rich in immunoglobulins and lysozymes and are the reason the eye can be exposed to ambient air without breakdown and infections. The tear film in and of itself has refractive properties and bends light with the power of approximately 0.5 diopter. Tears are basically trilaminal with an inner layer consisting of a mucoprotein that serves to decrease surface tension and allows the middle aqueous phase to spread out more uniformly over the cornea. This is produced by goblet cells within the conjunctival tarsus and limbus. The middle layer, or aqueous phase, is produced by the subconjunctival glands of Krause and Wolfring. The aqueous phase is augmented by the reflexly stimulated main lacrimal gland. Oil-producing glands such as the meibomian glands located in the upper and lower eyelids and the palpebral glands of Zeis and Moll provide an oily covering to the tears that prevent evaporative loss and provide stabilization and duration to the tear film. The reflexly stimulated lacrimal gland is divided into two portions by the lateral horn of the levator palpebrae superioris. The main orbital lobe is approximately three times the size of the palpebral lobe, and in many instances the palpebral lobe is visible with eversion of the upper lid (Fig. 1-16). Prolapse of this gland can be corrected by suspension with the use of surrounding periosteal sutures (Figs. 1-17 and 1-18).

Figure 1-17 The upper eyelid is everted, demonstrating a prolapsed lacrimal gland. Lacrimal gland prolapse must be distinguished

from subconjunctival orbital fat. The latter can be resected, and the former should be suspended, except in cases of malignancy, and so on.

Figure 1-18 An upper lid incision exposing the levator aponeurosis has been disinserted from the tarsal plate. The levator is thickened secondary to thyroid infiltrative disease. The lacrimal gland and orbital and palpebral lobes are visualized in their respective positions. The orbital lobe is prolapsed from its usual cephalic location within the lacrimal fossa. The lobes of the gland are divided by the lateral horn of the levator, which has been lysed surgically in this photograph.

The aqueous phase of tears is produced in the upper lateral fornix or cul-de-sac and then structured into three layers and distributed by means of the squeegee action of the upper and lower eyelids. These are distributed across the eye and then repeatedly pumped into and through the lacrimal system with the cyclic action of blinking. This forceful yet subtle muscular action eventually propels tears, which begin in the upper outer corner of the orbit, into the nasal cavity beneath the inferior turbinate.

In the context of cosmetic surgery one can see how easily the precorneal tear film can be disturbed by, for example, changing the pattern in which the eyelids mix, distribute, and pump tears. A patient who has borderline tear production and/or quality may be sufficiently altered by surgery so that he or she may complain of dry eyes or epiphora. A change in the refractive index of the precorneal tear film may lead the patient to complain of a change in the quality of his or her vision, even when objective testing (Snellen chart) does not discern a difference from the preoperative and postoperative examinations.

The blinking cycle is an important physiologic mechanism for draining tears. This mechanism is propulsive and, therefore, independent of gravity. The movement of tears into the nose is assisted by an active “lacrimal pump,” which is dependent on the superficial and deep heads of both the pretarsal and preseptal orbicularis oculi muscles as well as the lacrimal diaphragm, which is a condensation of fascia around the lacrimal sac (see Fig. 1-11). The canaliculi remain patent with the ampullae in contact with the tear lake formed in the medial canthus when the eyelids are open and the orbicularis oculi muscle is relaxed. On contracture of the orbicularis muscle, eyelid closure ensues with a milking of tears from superolateral to inferomedial over the ocular surface. Muscular contracture causes shortening of the canaliculi and closing of their ampullae. Concomitantly, the deep heads of the preseptal muscles attached to the fascia or lacrimal diaphragm dilate the

sac and, hence, create a negative pressure within its lumen. The closing of the ampullae with shortening of the canalicular system causes propulsion of tears medially, and the negative pressure generated within the lacrimal sac causes tears to be sucked into the sac nasally on eyelid closure. As the lids reopen, the orbicularis muscle relaxes, causing collapse of the lacrimal sac and propulsion of tears into the nose beneath the inferior turbinate along with a relaxation and lengthening of the canaliculi and a redilatation of the ampullae. This cycle repeats over and over again with efficient smooth drainage of tears (see Fig. 1-12). The lacrimal sac is approximately 15 mm in height with one third of it extending above or superior to the medial canthal tendon. The nasolacrimal duct refers to the intraosseous portion, and this is approximately 12 mm in length. The duct empties into the inferior meatus of the nose approximately 15 mm from the floor (see Fig. 1-11). To commit this to memory, I prefer to divide each of these three distinct vertical segments into 15-mm lengths.

The balance between tear production and evaporation is critical to patient comfort because this determines whether there is sufficient wetting of the corneal surface. Production of adequate tears is a function of both quantity and quality. That is, a patient may make a lot of tears as measured on Schirmer’s test but produce insufficient oils, which prevents evaporative loss to ambient air and, hence, may have a relatively dry eye despite adequate volumetric tear production. The homeostasis between production and evaporative loss is a critical concept in appreciating nuances in patient presentation and in deciding which procedures appropriately address aesthetic and/or reconstructive issues. For example, a patient who produces a small amount of good quality tears but has a small lid aperture that minimizes evaporative tear loss must be approached in a different way than the patient who has a large lid aperture (higher evaporative loss) with tears of a similar quantity and quality. Therefore, in choosing an appro-

priate procedure for a patient, one must take into account the aesthetic objectives and weigh those against the need to maintain an adequate precorneal wetting surface. Some patients may require an overall reduction in lid aperture, some may not tolerate an increase in aperture and maintenance is the goal, and still others may produce enough of a quality tear film so as to tolerate a larger lid aperture, which may be an ideal cosmetic result. The concept of production and evaporation, taking quantity as well as quality into account, should be part of the surgeon’s preoperative thought process for every patient. In some cases it may only require a few seconds, and the surgeon and patient may have great latitude in choosing an optimal procedure. In others it may require a more prolonged consideration and leave the surgeon and patient with few options. Nevertheless, this preoperative process will serve to limit postoperative complications and complaints.

HOMEOSTASIS OF THE LOWER EYELID

As we have discussed, the normal lower eyelid position is 1 to 2 mm over the corneoscleral junction, with the central lower eyelid being the lowest point with a gentle sweeping upward inclination toward the lateral and medial canthi. The lateral canthus is approximately 15 degrees more inclined than the medial canthus. If one views the lower eyelid as floating in space anchored between the medial and lateral canthi, there is a balance of forces maintaining this normal anatomic position. A knowledge of the forces acting on the lower eyelid and how they interact is important in understanding, treating, and providing prophylaxis against lower eyelid malposition. I like to term the forces holding the lower eyelid above the limbus and against the eye as intrinsic support. Intrinsic support is generated in part by cephalic

vector forces contributed by the tarsal plate. It is also produced by the cephalic and posterior support generated by the orbicularis muscular complex (anterior and posterior heads) and the medial and lateral canthal tendons. The tarsal plate integrates these appropriate vector forces by providing three-dimensional spatial orientation. There are physiologic forces always working on the lower eyelid whose net effect is to distract the lower lid inferiorly and anteriorly away from the globe. Generally, there is a balance or homeostasis of these forces with intrinsic support overcoming extrinsic distraction forces. Patients will be comfortable with an adequately shielded and wet cornea, provided intrinsic support is greater than extrinsic distraction forces (Fig. 1-19). There are two basic scenarios in which the normal balance of forces can be disturbed with distraction overcoming support. These are when intrinsic support is weakened by the normal senescent process or by intervention in which intrinsic support forces imparted by the canthal, tarsal, or muscular elements are surgically weakened. A second mechanism for displacement of the lower eyelid down and/or away from the globe is to increase distraction forces while maintaining intrinsic support forces intact. In this case, the lower eyelid would be displaced away from the globe by excessive distraction forces despite an intrinsic support mechanism that would otherwise be adequate. This scenario may be created by burns, contractures, or surgical intervention (e.g., excessive skin resection in a transcutaneous blepharoplasty, laser contracture, or chemical peels) (Figs. 1-20 and 1-21). Therefore, lower eyelid position is dependent on a balance of vector forces, with intrinsic support always exceeding extrinsic distraction forces in the maintenance of normal anatomic position. This normal anatomic position is critical in maintaining adequate corneal wetting, eliminating excessive evaporative loss, assisting in the physiologic squeegee and distribution effects of the lid, and maintaining an intact lacrimal pump mechanism, not to mention appropriate aesthetic appearance.

Intrinsic

Support

Forces (ISF)

Extrinsic

Distraction

Forces (EDF)

IS

ED

1.The orbital septum is confluent with the periosteum of the skull and orbit and serves as the defining structure of the deep orbit.

2.The orbital septum must be violated in order to access preaponeurotic and/or pre-capsulopalpebral fat.

3.Whitnall’s tubercle is a common insertion point for a number of structures, including the orbital septum, Lockwood’s ligament, Whitnall’s ligament, deeper aspects of the orbicularis, and check ligaments of the lateral rectus muscle.

4.The bony anatomic location of Whitnall’s tubercle (below the lacrimal fossa and several millimeters within the orbit) must be appreciated to properly execute lateral canthal suspension procedures.

5.The upper and lower eyelids and orbit are anatomically analogous and are suspended in space by the medial and lateral canthal anchors. The eyelids are laminar, like most structures in the body (external, middle, and lining).

6.In the lower eyelid, the post-orbicularis pre-capsulopalpebral space is fundamental in the execution of both transconjunctival and transcutaneous procedures.

7.The capsulopalpebral fascia is an extension off the extraocular muscles and is always divided at some level in the transconjunctival route to the orbit.

8.The levator palpebrae superioris runs horizontally from the lesser wing of the sphenoid and reorients to a vertical direction at Whitnall’s ligament.

9.Whitnall’s ligament divides the lacrimal gland laterally where it contributes to the lateral retinaculum. Medially it anchors on the trochlear.

10.The anatomic complexity at Whitnall’s tubercle can lead to complications from canthopexy procedures. For example, care must be taken to exclude the lateral horn of the levator in lateral canthal suspension procedures.

11.The fascial system of the orbit provides a scaffold that extends intraand extraconally from anterior to posterior within the orbit. This system allows the transduction of forces from one location to another distant site within the orbit.

12.The greater wing of the sphenoid is the primary delineator of the orbit from the middle cranial fossa. Laterally it articulates with the zygoma.

13.The extraocular muscles serve as conduits for the blood supply to the anterior eyeball. Disinsertion of more than two muscles can lead to anterior segment necrosis.

14.The inferior oblique muscle is most anterior in the orbit, followed by the superior oblique muscle. They should be visualized and protected in retroseptal dissections. Both muscles delineate the medial from the central fat compartment.

15.The medial canthus is enveloped by deep and superficial muscular and fascial extensions, which contribute to the active lacrimal pump mechanism.

16.Significant medial canthal laxity can lead to a displaced and compromised lacrimal pump when a lateral canthal tightening procedure is performed alone. This problem can be obviated with a concomitant medial canthal tightening.

17.Division of the lateral canthal tendon in and of itself is not sufficient to mobilize the lower and/or upper eyelid.

18.The lateral canthus is optimally inclined, compared with the medial canthus, from an anatomic, physiologic, and aesthetic point of view.

19.In the upper lid, all the fat that is altered (removed, repositioned, grafted) is preaponeurotic.

20.Orbital hemorrhage and possible visual loss can be produced by traction on the most anterior orbital fat.

21.Tears are trilaminar, are important for corneal integrity, and have refractive properties.

22.Eyelid integrity and the blinking cycle are important for proper tear distribution and drainage.

23.The balance between tear production and evaporative tear loss determines whether there is sufficient corneal wetting. The third element in this equation is tear quality.

24.The surgeon can alter evaporative loss by changing eyelid aperture.

25.The lower eyelid is suspended in space, and its normal anatomic position is sustained by a balance between intrinsic supportive and extrinsic distraction forces.

26.The tarsal plate provides spatial orientation and integrates components of the intrinsic support system.

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