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

Figure 1-7 The eight bones of the orbit basically create two significant facial buttresses, the frontal- zygomatic-maxillary and the frontal- nasal-maxillary. The sphenoid articulates with the zygoma and is the major delineator between the middle cranial fossa and the orbit. The optic foramen is in the body at the sphenoid. Medially, the lacrimal fossa is visualized between the anterior and posterior lacrimal crests. These crests serve as insertions for respective elements of the medial canthal tendon. The lacrimal sac lies within the fossa, between the anterior and posterior crests. Whitnall's tubercle is seen lying 2 to 3 mm within the orbit and 6 to 8 mm below the lacrimal fossa. The position of this important tubercle is salient in performing an anatomically functional and aesthetic canthoplasty procedure.

Lacrimal fossa

Zygomatico frontal suture

Whitnall's

tubercle

Zygomaticofacial

foramina

Inferior orbital fissure

Lacrimal bone

Zygomatic bone

Lacrimal fossa

Infraorbital foramen

Maxilla bone

EXTRAOCULAR MUSCLES

The so-called check ligaments serve to prevent extremes in extraocular muscle excursion with resulting snapping or uncontrolled spastic movements. The versions or movement of the eyeball is controlled by the extraocular muscles. The fascial system within the orbit supports the globe and limits ocular movement. This fascial system provides an interconnecting scaffold from one structure to the other and extends both extraconally (outside the muscle cone) and intraconally, transgressing the orbital fat. The extraocular muscles form a conical network within the orbit with the apex forming the origin of the extraocular muscles at a fibrous thickening of the periosteum known as the annulus of Zinn (Fig. 1-8A). The orbital apex delineated by the greater sphenoid wing separates the middle cranial fossa from the orbit, and it is at this juncture where a number of nerves pass between the intracranial compartment and the orbit. These include the optic, oculomotor, trochlear, and abducens nerves. The superior oblique and the levator muscles arise at the orbital apex but outside the common tendinous ring of Zinn. The functions of the extraocular muscles include not only abduction and adduction but also intorsion and extorsion. These latter functions allow the world to remain upright when one tilts one’s head toward the shoulders. Of course this is all orchestrated by the vestibulocochlear system and the brain stem. The vascular supply to the extraocular muscles is principally from the ophthalmic artery, with each muscle receiving two anterior ciliary arteries, except for the lateral rectus, which

receives only one. The anterior ciliary arteries continue on to penetrate the sclera of the eyeball beyond the muscular insertions and thus contribute significantly to nourishing the anterior segment of the globe. Therefore, disinsertion of more than two rectus muscles from the globe can result in anterior segment necrosis.

Two important muscles in anterior orbital surgery are the inferior oblique and, to a lesser extent, the superior oblique. The inferior oblique is the most anterior muscle within the orbit and is the most commonly damaged muscle in blepharoplasty or surgical approaches to the orbital rim and zygoma in fracture treatment. The inferior oblique muscle originates from the periosteum lateral to the nasolacrimal canal and then courses posteriorly and laterally within the orbit to insert on the eyeball. Therefore, one can see by the origin and insertion the mechanical results of its contraction on the globe. These are primarily elevation, secondarily abduction, and finally extorsion or rotating the eyeball clockwise as viewed from inside the skull. The superior oblique muscle that arises superomedial to the annulus of Zinn functions in depression, abduction, and intorsion. From a practical standpoint, the inferior oblique muscle should always be identified in transconjunctival blepharoplasty, as it divides the medial and central fat pads. In a transcutaneous route this is less important; however, I prefer to identify it in every approach. The superior oblique muscle divides the medial and central fat pads in the upper compartment, and, although it arises at the orbital apex, it changes direction and vector forces after looping around the trochlear in the superomedial orbit, producing a near mirror image of the vector forces created by the inferior oblique muscle (see Fig. 1-8).

THE MEDIAL CANTHUS

The medial canthus contains a number of structures compactly arranged in a small space oriented around the lacrimal fossa. Pretarsal, preseptal, and preorbital orbicularis oculi fibers have both superficial and deep heads, and these components envelop the lacrimal sac, inserting on the anterior and posterior lacrimal crest, respectively. The medial canthal tendon extends beyond the anterior lacrimal crest to the frontal process of the maxilla and like the orbicularis oculi fibers has both anterior, posterior, and even a superior component (Fig. 1-9). The anterior and posterior components of the medial canthal tendon similarly envelop the lacrimal sac. Hence, the lacrimal system is an active pump mechanism in which orbicularis fibers inserting on fascia surrounding the lacrimal sac actively dilate and passively contract the sac, altering pressure within the middle and distal lacrimal system. These orbicularis fibers also envelop the canaliculi of the upper and lower lids, allowing this proximal aspect of the lacrimal drainage system to alter length and width with cyclical muscular contraction.

The medial canthus is less likely to be addressed in standard cosmetic and periocular surgery, that is, in the absence of nasal orbital ethmoid trauma and/or elective osteotomies. However, there are instances in which the medial canthal tendinous complex needs to be

addressed. Generally, the upper and lower puncta lie midway between the caruncle or medial lid commissure and the medial limbus (corneal scleral junction). Laxity of the medial canthal tendinous complex produces both lateral and inferior displacement of the medial commissure and canaliculi. This is especially true when concomitant lateral canthal laxity is noted and the surgeon chooses to address the lateral canthal complex with a tightening or suspension procedure. In these instances, the laxity of the medial canthal tendon allows the puncta to be displaced temporally on lateral canthal tendon tightening alone. This can have significant consequences in terms of tear drainage and patient discomfort. The surgeon must be cognizant of significant laxity in the medial canthal complex when he or she chooses to tighten or suspend the lower lid. In these cases, the medial canthal tendon may require plication or reefing before lateral canthal tightening, to obviate displacement of the lacrimal drainage system. In plication or suspension of the medial canthal tendinous complex, one must be aware of the course of the lacrimal drainage system and protect it. I recommend intubation of the lacrimal system as a prophylactic measure in many cases (Fig. 1-10). The lacrimal pump refers to the dynamic nature of the medial canthal complex, including the lacrimal sac, which sits between the anterior and posterior lacrimal crest with two thirds of it lying within the bony fossa.

Figure 1-9 The medial canthal tendon envelops the lacrimal sac. It is tripartite, with anterior, posterior, and superior limbs. Like the lateral canthal tendon, its limbs are continuous with the tarsal plates. The components of this tendon along with its lateral counterpart are enveloped by deep and superficial aspects of the orbicularis muscle. This arrangement is important in maintaining a functional and active lacrimal drainage system. The upper, lower, and common canaliculi closely approximate this tendon system; and care should be taken to preserve their integrity when altering any aspect of the medial canthal tendon. This tendon may require an elective tightening procedure, especially in cases in which a lateral canthal procedure alone would produce punctal and lacrimal dystopia.

Posterior limb,

medial canthal tendon

Superior limb,

medial canthal tendon

Anterior limb,

medial canthal tendon

Lacrimal fossa

Anterior and posterior lacrimal crests

The upper and lower canalicular systems are basically two pipes connected to the lacrimal sac, which in 90% of instances coalesce into a common canaliculus. Each system is approximately 2 mm in vertical height and 6 to 8 mm in horizontal distance before coalescing with the lacrimal sac. The lower canaliculus is slightly more lateral than the upper; and this entire system, as mentioned earlier, is enveloped by superficial and deep heads of the orbicularis muscle and respective components of the medial canthal tendon (Fig. 1-11). The lacrimal sac dilates and collapses with different phases of the blinking process and, hence, is an extremely

active or dynamic process that does not depend on gravitational forces. The lacrimal pump is related to orbicularis muscle contraction and relaxation and therefore cycles with blinking (Fig. 1-12). Tear drainage is independent of head position; therefore, epiphora does not generally occur even while one stands on his or her head. Cosmetic or reconstructive surgical procedures in addition to trauma can disrupt fibers of the orbicularis muscle, causing anatomic and/or physiologic alterations in lacrimal drainage and creating symptoms (Figs. 1-13 and 1-14).

Figure 1-13 Close-up view of the medial canthal region of a postoperative patient shown in Figure 1-14. Note the upper and lower canalicular system intubated with silicone tubes that course through the lacrimal sac and into the nose. The lower punctum is more lateral than the upper punctum.

Figure 1-14 The medial canthal incision is shown with the lacrimal sac reflected laterally out of the lacrimal fossa. Medially behind the retracted skin edge is the anterior lacrimal crest. The lower portion of the sac is fixed by the superior portion of the nasolacrimal duct that drains into the inferior meatus of the nose.