Skin creases and folds

Several lines on the skin serve to anatomically define the periocular and facial anatomy. The upper eyelid skin crease separates the upper eyelid skin fold from the flat pretarsal component of the upper eyelid (Figure 2-1). In your study of oculoplastic surgery, you will see that the upper eyelid crease is an anatomic landmark that is commonly referred to in oculoplastic surgery. Incisions hidden in this crease for upper eyelid ptosis repair or blepharoplasty and other procedures are among the most common incisions that you will use in oculoplastic surgery.

Figure 2-1 Surface landmarks of the periorbital area. The facial wrinkles are oriented 90 degrees to the underlying muscle.

The eyelid skin above and below the crease is the thinnest in the body. The skin must be thin to allow for the spontaneous quick blinking movements of the eyelids. A lower eyelid crease is common in children (Figure 2-2), but is usually not visible in adults. The eyelid skin becomes thicker as you move further away from the eyelid margins toward the brow and cheek. The nasojugal and malar folds separate the thin lower eyelid skin from the thicker skin of the cheek. In younger patients, the inferior orbital rim contour is not visible or easily palpable. With age, the malar fat pad (sometimes called the suborbicularis oculi fat or SOOF) descends, and the rim becomes more noticeable, both visually and by palpation (compare some of your 20-year-old patients with your 50-year-old patients in this regard). The melolabial fold extends inferolaterally from the ala of the nose to the corner of the mouth. Subtle facial asymmetry resulting from paralysis of the facial nerve is often evident in the melolabial fold where the fold is softer or absent.

Figure 2-2 The lower eyelid crease, usually seen only in children.

Skin creases (rhytids or wrinkles) form as a result of the movement of the underlying muscles of facial expression. The most familiar of these creases are the “crow’s feet” arising at the lateral canthus caused by contraction of the orbicularis muscle. The direction of these wrinkles can be predicted by recognizing that they always form perpendicular to the underlying muscle fibers (Figures 2-3 and 2-16). This explains the radial orientation of the crow’s feet lines to the circular orientation of the orbicularis muscle. Other prominent creases caused by underlying muscle contraction that you will see include the horizontal forehead furrows and the vertical and horizontal lines of the glabella. These lines suggest redundancy in the tissue perpendicular to the lines. That redundancy represents lax tissue that is “tightened” to reverse aging changes. The same redundancy is what you are looking for when you are trying to close a tissue defect after excision of a facial skin cancer. You will also learn to hide incisions in these creases so that the resulting scar is not easily seen.

Figure 2-3 “Happy face” demonstrating how brow position reflects mood

(after Ellenbogen R: Transcoronal eyebrow lift with concomitant upper blepharoplasty. Plast Reconst Surg 71(4):490–499, 1983).

The eyebrows

The brows, technically a part of the scalp, are divided into three anatomic parts:

The orientation of the brow hairs varies in each part of the brow. The brow hairs in the head of the brow tend to be vertical. As you move toward the tail of the brow, you will notice that the hairs tend to lie flatter or slightly downward. It has been suggested that incisions made within the brow hairs should be oriented parallel to the shafts of the hairs to minimize the number of follicles damaged. This seems reasonable, but makes closure of the wound more difficult.

The eyebrows are an important feature of an individual’s facial appearance and are primary indicators of facial expression and mood. Look at Figure 2-3. Many texts include variations of this “happy face” eyebrow model. Look at your friends’ brows carefully and you will be impressed by how the slope, shape, and position of the eyebrows give you an immediate impression of mood. You will be impressed to see that lifting a drooping tail of the brow will make a melancholic-appearing patient look happier. We will see this later in Chapter 6.

The male and female brows differ in shape and position (Figure 2-4). The normal male brow is flat and full in contrast to the thinner and more arched female brow. The superior margin of brow hairs is “feathered” in men and smooth in women. The male brow sits squarely at the superior orbital rim. The female brow is typically arched, with the highest point being above the lateral canthus or slightly more medial. The position of the female brow is well above the rim, especially temporally, where the superior lateral part of the bony rim contour is visible and easily palpable. The male rim is generally more prominent than the female rim because of a larger frontal sinus. The male brow tends to encroach upon the otherwise hairless glabella between the brows.

Figure 2-4 Normal eyebrow contour. (A) Female. (B) Male.

The features of the brow are secondary sexual characteristics that differ in men and women. Women manicure the brows to make the female face more attractive. Epilation of the brow hairs accents differences between male and female brows in thickness, smooth margins, arched contour, and position. Although the shape and position of the brow change some with the current fashion, I suspect we all have the same image of male and female movie supermodel eyebrows. With age, the appearance of the brow changes also. The normally high arch of the young woman is lost as the brow tends to droop temporally. A ptosis of the brow accentuates the upper eyelid skin fold and fills in the deep superior sulcus of the upper eyelid seen in younger patients. Lifting a drooping eyebrow always improves the appearance of a cosmetic blepharoplasty. With a severe brow ptosis, as in facial nerve palsy, the superior visual field is obstructed. Lifting the brow will help to restore the visual field. You can see that your appreciation of the eyebrow anatomy is important for you to do cosmetic or reconstructive surgery of the face.

The eyelids

The function of the eyelids is to protect the eyes and distribute the tears. It is important for you to understand the normal anatomy of the eyelids and to recognize conditions that may prevent normal function.

The lateral canthus is usually slightly higher than the medial canthus, although the slope of the eyelid fissures can vary widely among individuals (see Figure 2-1). The upper lid contour is more arched than that of the lower lid. The peak of the upper lid is just nasal to the pupil. The lowest point of the lower eyelid is below the lateral limbus. The normal contour of the eyelid must be recreated in a variety of procedures, including ptosis repair and reconstruction of the lateral canthal angle.

The horizontal length of the eyelids is 30 mm. The distance between the upper and lower eyelids, the palpebral aperture or fissure, is about 10 mm. A useful way to measure the position of the upper and lower eyelids is the margin reflex distance. This distance is the number of millimeters from the corneal light reflex to the lid margin. The upper lid margin reflex distance (MRD₁) usually measures 4–5 mm. That means that the upper lid margin rests slightly below the limbus. The lower lid rests at the lower limbus, making the lower lid margin reflex distance (MRD₂) 5 mm (Figure 2-5). These distances can be measured with a ruler or estimated. When you estimate the distance, keep in mind that midway between the corneal light reflex and the limbus is 2.5 mm. The eyelid aperture measurements, especially the MRD, are an essential part of the eyelid examination, one of the eyelid vital signs. A drooping upper eyelid is known as ptosis or blepharoptosis. An upper eyelid resting above the upper limbus or a lower eyelid resting below the lower limbus is said to have lid retraction. The white between the limbus and the lid is known as scleral show.

Figure 2-5 The margin reflex distance.

There are three or four rows of eyelashes along the upper lid margin and one or two rows of eyelashes along the lower lid margin. The eyelashes extend from just lateral to the puncta to the lateral canthus. Misdirection of the eyelashes against the eye, also known as trichiasis, causes a foreign body sensation. In some cases, trichiasis can cause severe corneal problems. Treatment is focused at redirecting or eliminating the eyelashes.

The eyelids attach to the orbital bones via the medial and lateral canthal tendons. The tendons attach to the tarsal plates, which are the fibrous skeleton of the eyelids. A favorite board examination question asks if the tarsal plates are made of cartilage (which they are not; they are made of fibrous tissue). The upper lid tarsal plate is about 10 mm high, corresponding with the skin crease height. The lower lid tarsal plate is about 4–6 mm high. Within the tarsal plates are the meibomian glands, modified sebaceous glands that secrete the majority of the oil layer of the tear film. The eyelash follicles originate on the anterior surface of the tarsal plate and exit the eyelid on the margin. The orbicularis muscle is tightly bound to the anterior surface of the tarsus.

The orbital rim

The bones of the orbital rim

Let’s move from the superficial anatomy to the deep anatomy, the orbital bones. The orbit is made of a strong bony rim and relatively weak orbital walls. Several openings, foramina, into and out of the orbit allow the passage of the veins, arteries, and nerves that supply the orbital tissues. We will discuss the orbital rims, walls, and foramen in the paragraphs below.

The orbital rim provides protection for the eye without compromising visual field. The rim is made of thick strong bones, especially the superior and lateral rims where protection from injury is needed most. The superior orbital rim protects the eye from blows from above as well as sunlight (you will rarely see skin cancers on the upper eyelid). The lateral orbital rim curves posteriorly so that there is good peripheral vision at the sides. The inferior rim is posterior enough so that the inferior visual field is not blocked for close work and reading. The orbital rim is made of three bones, the frontal, the zygomatic, and the maxillary (Figure 2-6).

Figure 2-6 The frontal view of the orbit.

Tripod fracture

Rarely do the bones of the superior and lateral rims themselves break. More commonly, the suture lines between the bones separate. The most common facial fracture is a zygomaticomalar complex fracture (ZMC fracture) (Figure 2-7). In this fracture, the zygoma is separated from the other orbital bones at the sutures connecting the zygoma to the rim. Fracture or separation occurs superiorly at the frontozygomatic suture and inferiorly at the zygomaticomaxillary suture. A fracture also occurs along the zygomatic arch posteriorly at the suture line between the temporal bone and zygoma. Because three suture lines are fractured, this type of fracture is also known as a tripod fracture. The bones of the medial and inferior rims are not as strong as the superior and lateral rims. Injury to the medial and inferior rims may cause the bones to fracture in many pieces, a comminuted fracture.

Figure 2-7 “Tripod” or zygomatic malar complex fracture (ZMC fracture). Note that the left lower lid and lateral canthus are displaced inferiorly.

The orbital rims provide the sites for attachment of the medial and lateral canthal tendons. Look at a skull or Figure 2-8. Follow the inferior and superior rims as they form the medial orbital rim. You will notice that the paths of the rims diverge. The superior rim moves posteriorly to form the posterior lacrimal crest. The inferior rim moves anteriorly to form the anterior lacrimal crest. The fossa between the two crests is the lacrimal sac fossa where the lacrimal sac sits. The medial canthal tendon splits into two limbs, the anterior and posterior limbs, which attach to the lacrimal crests, respectively, surrounding the lacrimal sac (Box 2-2).

Figure 2-8 Anterior and posterior lacrimal crests diverge to form the lacrimal sac fossa.

Box 2-2 The Orbital Rim

Superior rim

• Frontal bone

Lateral rim

• Zygomatic bone

Medial rim

• Frontal bone

• Zygomatic bone

Inferior rim

• Zygomatic bone

• Maxillary bone

The orbital walls

Boundaries of the walls

There are four orbital walls. The walls angle posteriorly to form a conical or pyramidal orbit. The orbital roof is concave in contour and forms the floor of the anterior cranial fossa. The concavity of the orbital roof is particularly steep laterally and anteriorly where the lacrimal gland sits in the lacrimal gland fossa. The orbital roof is separated from the lateral orbital wall by the superior orbital fissure (Figure 2-9; see also Figure 2-7). The lateral orbital wall (Figure 2-10; see also Figure 2-6) is relatively flat on the orbital side, but curved on its exterior surface to accommodate the temporalis muscle. The inferior orbital fissure separates the lateral wall from the orbital floor (Figure 2-11). The orbital floor is the roof of the maxillary sinus. The orbital floor slopes upward posteriorly to the apex and medially toward the medial orbital wall. The medial orbital wall is the lateral wall of the ethmoid sinus. Notice that both the medial wall and the floor are normally convex. The anatomic separation of the medial wall and orbital roof is the suture line separating the ethmoid bone and the frontal bone (the frontoethmoid suture) (Figure 2-12). This suture line is easy to see because the anterior and posterior ethmoid arteries and nerves travel through the foramina in the suture line.

Figure 2-9 The orbital roof.

Figure 2-10 The lateral wall of the orbit.

Figure 2-11 The floor of the orbit.

Figure 2-12 The medial orbital wall.

Fissures, foramina, grooves, and canals

There are several openings into and out of the orbit (Table 2-1). I like to think about what these openings are for. What spaces do the openings connect? Once you know what spaces are connected, it’s easier to remember what goes through the openings. The most obvious of these are the superior and inferior orbital fissures. These fissures form a V on the lateral side of each orbit. As we said, the superior orbital fissure separates the roof from the lateral wall, and the inferior orbital fissure separates the floor from the lateral orbital wall. See if you can visualize this (if you can’t, look at Figure 2-6). Because the superior orbital fissure connects the orbit to the brain, it must carry cranial nerves to the orbit (cranial nerves III, IV, and VI). The inferior orbital fissure connects the orbit to the infratemporal fossa and the pterygopalatine fossa (“behind and around the maxillary sinus”—posterior and lateral to the maxillary sinus).

Table 2-1 Fissures, foramina, grooves, and canals

Opening	From orbit to	Contains
Superior orbital fissure	Cavernous sinus	Cranial nerves III, IV, and VI Superior ophthalmic vein
Inferior orbital fissure	Pterygopalatine fossa	Inferior ophthalmic vein
Foramen rotundum	Brain	Maxillary nerve (V2)
Optic canal	Chiasm	Optic nerve (cranial nerve II)
Anterior ethmoidal foramen	Sinus mucosa	Anterior ethmoidal artery, vein, and nerve
Posterior ethmoidal foramen	Sinus mucosa	Posterior ethmoidal artery, vein, and nerve
Zygomaticotemporal foramen	Superior lateral orbital rim tissues	Nerve, artery, and vein
Zygomaticofacial foramen	Inferior lateral orbital rim tissues	Nerve, artery, and vein
Bony nasolacrimal duct	Inferior meatus of nose	Membranous nasolacrimal duct

At the apex of the V formed by the superior and inferior orbital fissures is the infraorbital groove (Figure 2-11). As the groove extends anteriorly along the orbital floor, it gets a bony covering and is known as the infraorbital canal. The canal leaves the orbit at the infraorbital foramen. As you would assume, the infraorbital nerve travels in the infraorbital groove and through the infraorbital canal. The infraorbital nerve is the major sensory nerve of the second division of the trigeminal nerve. Go back to the apex of the V. Follow the infraorbital groove posteriorly and you will be in the pterygopalatine fossa. This fossa, as mentioned earlier, is the space posterior to the maxillary sinus and anterior to the skull base (the bottom of the cranial vault). The trigeminal nerve leaves the cranium through the foramen rotundum, entering the pterygopalatine fossa. The trigeminal nerve then crosses the fossa and enters the orbit via the posterior portion of the inferior orbital fissure, the infraorbital groove.

Let’s talk about the other important opening out of the orbit into the cranium, the optic canal. The optic nerve leaves the orbit via the optic canal to enter the cranial vault. Look at Figure 2-6 or at a skull. The optic canal is the most posterior landmark in orbit. The length of the optic canal is 10 mm. Medially, the posterior ethmoid foramen is 4–7 mm anterior to the optic canal, an important surgical landmark when operating deeply along the posterior orbital wall (see Figure 2-12). Laterally, the optic canal is separated from the superior orbital fissure by a small piece of bone, the optic strut. If you follow the optic strut posteriorly and superiorly, it becomes the anterior clinoid process. Although not important for you now, if you approach the optic canal from an intracranial exposure with your neurosurgical colleagues, knowledge of this relationship may help you. (Next time you pick up a skull, look at how the optic strut extends to form the anterior clinoid process. It will help you learn some of this complicated anatomy.) When you look at a computed tomography (CT) scan, the thin piece of bone separating the optic canal from the superior orbital fissure is the optic strut. Earlier, we said that the posterior portion of the lateral orbital wall was made up of the greater wing of the sphenoid bone (Figure 2-13). The optic strut and the optic canal are a part of the lesser wing of the sphenoid bone. The sphenoid bone forms a large part of the skull base and posterior orbit. Its shape is complicated. For now, just remember that the greater wing lies lateral to the superior orbital fissure and the lesser wing lies medial to the superior orbital fissure.

Figure 2-13 Axial CT scan of orbit. (A) Superior orbital fissure. (B) Optic canal. (C) Anterior clinoid process. You can see how the inferior extension of the anterior clinoid process, the optic strut, separates the optic canal from the superior orbital fissure. When you want to identify the optic canal, find the scan that shows the anterior clinoid process. Arrow points to optic canal fracture.

Look at the CT scans shown in Figure 2-13. It is easy to recognize the superior orbital fissure because it opens into the intracranial space. Similarly, it is easy to recognize the inferior orbital fissure because it opens into the space posterior to the maxillary sinus (the pterygopalatine fossa) and into the infratemporal fossa laterally. The inferior orbital fissure does not open into the brain. The optic canal is adjacent to the anterior clinoid processes (seen on the same CT cut). The optic canal also opens into the intracranial space.

There are two other sets of foramina to mention. All carry the related arteries, veins, and nerves. These foramina are:

• Anterior ethmoidal

• Posterior ethmoidal

• Zygomaticotemporal

• Zygomaticofacial

The anterior and posterior ethmoidal foramina are important surgical landmarks along the medial orbital wall. These foramina are found in the frontoethmoid suture. If you break the medial wall inferior to the suture, you will be in the ethmoid sinus. If you break the bone above the suture, you will be in the brain (causing a cerebrospinal fluid (CSF) leak). The anterior–posterior location of the foramina is a helpful indicator of how far posterior an orbital dissection along the medial wall is proceeding. The anterior ethmoidal foramen is about 24 mm posterior to the anterior lacrimal crest. The posterior ethmoidal foramen is another 10–12 mm posterior. As we already mentioned, the optic canal is 4–7 mm more posterior. A helpful way to remember is 24–12–6 mm. During an operation, it is easy to overestimate your position on the medial orbital wall, so these numbers are surprisingly helpful as you learn orbital surgery. When you operate along the medial orbital wall, it is important to recognize the ethmoidal vessels because significant bleeding can occur if they are inadvertently torn. The ethmoidal veins are valveless and permit flow into the orbit from the ethmoid sinus. Purulent sinusitis can spread into the orbit through these vessels or directly into the orbit through the thin lamina papyracea of the medial orbital wall. We will talk more about the vessels and sensory nerves that travel in these foramina later.

The zygomaticotemporal and zygomaticofacial foramina transmit the arteries, veins, and nerves of the same name. The nerves are sensory branches of the trigeminal nerve (V₂). The arteries are small branches that originate off the lacrimal artery (a main branch of the ophthalmic artery, which arises directly off the internal carotid artery). You will see these foramina when you lift the periorbita off the lateral wall. Cauterization is appropriate before you cut the arteries. If the artery retracts into the foramen, bleeding can be stopped by packing the foramen with a bit of bone wax. Cutting these nerves during a lateral orbitotomy results in some hypesthesia of the surrounding area that is minimal because of collateral innervation. Note that the overlap of these vessels and nerves with adjacent vessels and nerves of differing origin is typical of the collateral innervation and vascularization of the facial area. Infraorbital arterial branches (from the internal maxillary artery) medially and inferiorly overlap with the branches of the ophthalmic artery above. Anastomoses of the zygomaticotemporal nerve (from V₂) with the lacrimal nerve (from V₁) provide sensory overlap. This overlap of blood and nerve supply helps to preserve function after accidental trauma. Incisions can be made and flaps formed with relatively low risk of ischemia or sensory loss.

The periorbita

The bones of the orbit are covered with periosteum like all the other bones of body. The periosteum covering the inside of the orbit is known as the periorbita. The periorbita is tightly adherent to the bone at the orbital suture lines and along the orbital rims. Over the orbital walls, the periorbita is loosely adherent. You will see these differing degrees of adhesion when pus or blood accumulates under the periorbita as a result of infection or trauma. The periorbita is elevated off the orbital walls in a characteristic dome-shaped elevation ending at suture lines where the periorbita is adherent (Figure 2-14). The orbital septum is an extension of fibrous tissue continuous with the periosteum, extending from the orbital rim to lids. Where the orbital septum attaches to the rim is known as the arcus marginalis. Three structures meet at the arcus marginalis, the orbital septum, the periorbita, and the periosteum. We will discuss the orbital septum in more detail later.

Figure 2-14 Subperiosteal abscess on the orbital roof and the medial wall of the orbit attributable to ethmoid sinus infection. Note how the abscess elevates the periorbita to form a dome. The periorbita remains fixed to the frontoethmoid suture (arrow), making two abscess spaces.

Checkpoint

Imagine having a skull in your hand. You should be able to point out 5 or 10 minutes’ worth of bone anatomy and some of the clinically relevant features:

• Name the bones of the orbital rims. Which bone rarely breaks? Point to the fracture lines of a ZMC fracture?

• Describe the boundaries of the orbital walls. Name the bones of the walls. Where does a blowout fracture occur? Why is hypesthesia of the infraorbital nerve and subcutaneous emphysema common? What are other signs of a blowout fracture?

• Name three openings in the orbital walls and describe what spaces they connect. Try to identify these on each orbital axial CT scan:

— Optic canal

— Superior orbital fissure

— Inferior orbital fissure

• What two openings in the orbit form a V?

• What structure separates the superior orbital fissure from the optic canal?

If you know the answers to these questions, you are doing very well. If not, review the last section. This is basic information that you should know.

The orbicularis muscle

For the eyelids to function, there must be muscles that close the eye and muscles that open the eye. The orbicularis muscle (Figure 2-15) is the muscle primarily responsible for closing the eyelids. The orbicularis muscle is anatomically divided into the pretarsal portion, the preseptal portion, and the orbital portion. The pretarsal and preseptal portions overlay the tarsus and the septum, respectively. These muscles are responsible for involuntary spontaneous blinking. The orbital portion covers the orbital rims and is responsible for forced eyelid closure. All parts of the orbicularis muscle are innervated by the facial nerve with innervation entering from the underside of the muscle like all muscles of facial expression.

Figure 2-15 Muscles that close the eyes.

The corrugator and procerus muscles

Other protractors of the eyelids (protractors being the opposite of retractors, which open the eyes) include the corrugator muscle and the procerus muscle (Figure 2-15). The corrugator muscle originates on the bone of the superonasal rim and inserts into the skin of the head of the eyebrow. Firing of the corrugator muscle pulls the heads of the eyebrows together and makes the vertical furrows of the glabella (Figure 2-16). The procerus muscle originates on the frontal bone above the glabella and inserts into the skin of the glabella. The action of these vertically oriented muscle fibers pulls the heads of the brows inferiorly and causes the horizontal furrows of the glabella.

Figure 2-16 The glabellar furrows. (A) Corrugator muscle action causing vertical furrows in the glabella. (B) Procerus muscle causing horizontal furrows in the glabella.

Underactive muscles: facial nerve palsy

A number of clinical problems result from under- or overactivity of the muscles that close the eyes. Facial nerve palsy results in poor eyelid closure seen as lagophthalmos (the eyelids do not close with passive lid closure) or an incomplete spontaneous blink (quick normal blinks that do not completely cover the cornea). All the facial muscles on the affected side are also weakened, resulting in the brow ptosis, flattening of the melolabial fold, and drooping of the corner of the mouth that you have seen in patients.

Overactive muscles: orbicularis myokymia, facial tics, essential blepharospasm, and hemifacial spasm

The disorders resulting from overactivity of the orbicularis muscles are orbicularis myokymia, facial tics, essential blepharospasm, and hemifacial spasm. Probably you have suffered from orbicularis myokymia at one time or another. Hyperexcitability of the muscle, caused by stress or lack of sleep, causes a quick twitch of a few muscle fibers. Orbicularis myokymia is self-limited and usually lasts a few days or less. The other conditions involve different patterns of overactivity of the facial muscles, including the orbicularis muscle. These will be discussed in detail later in Chapter 9.

The lateral canthal tendon

Before we leave the topic of the orbicularis muscle, we should discuss the canthal tendons. As we have already noted, the canthal tendons attach the eyelids to the lateral and medial orbital rims (Figure 2-17). The tendons are extensions of the orbicularis muscle that attach to the periorbita overlying the bone. The anatomy of the lateral canthal tendon is easy to understand (Figure 2-18, A). The pretarsal and preseptal portions of the orbicularis muscle of each eyelid taper to form the superior and inferior limb of the lateral canthal tendon. The upper and lower limbs unite to form the lateral canthal tendon, which attaches to the inner aspect of the lateral orbital rim on Whitnall’s tubercle. Imagine the lateral canthal tendon complex as a Y lying on its side with contributions from both the upper and the lower eyelids.

Figure 2-17 The canthal tendons.

Figure 2-18 (A) The lateral canthal tendon. (B) The medial canthal tendon. (C) The medial canthal tendon complex surrounding the lacrimal sac.

Lower eyelid laxity: the cause of ectropion

In the following chapters, you will learn that proper horizontal tension on the lower eyelid is necessary for the eyelid to maintain its position. Laxity of the lower eyelid is the major cause of lower eyelid eversion or ectropion (Figure 2-19). This laxity does not occur from stretching of the tarsal plate; rather, it is attributable to lengthening of the lateral canthal tendon with age. You may have heard of older patients stating that their eyes look smaller than they did in their youth. You have probably already noticed that, with age, the upper eyelid droops (ptosis) and the lower eyelid actually rises up a bit (stretching of the lower eyelid retractors). Less apparent, but equally common, is a horizontal narrowing of the eyelid as a result of stretching of the canthal tendons. Thus, the “small eyes” that your older patients may notice are caused by both horizontal and vertical narrowing of the palpebral fissure.

Figure 2-19 Involutional ectropion of the lower eyelid caused by horizontal lid laxity, the result of stretching of the canthal tendons.

The medial canthal tendon

The medial canthal tendon is much more complex than the lateral canthal tendon because of the relationship of the medial canthal tendon to the lacrimal drainage system. The pretarsal and preseptal portions of the orbicularis muscle extend medially to form the two limbs of the medial canthal tendon (Figure 2-18, B). You will recall from the discussion of the anatomy of the medial orbital rim that the anterior limb attaches to the frontal process of the maxilla along the anterior lacrimal crest. The posterior limb attaches at the posterior lacrimal crest. Remember that the two limbs of the tendon surround the lacrimal sac (Figure 2-18, C).

The levator muscle

Two muscles are responsible for opening the upper eyelids, the levator muscle and Müller’s muscle. The levator muscle is the primary retractor of the upper eyelid. This skeletal muscle is responsible for voluntary elevation of the upper eyelid. Innervation to the levator muscle is via the superior division of the third cranial nerve (the oculomotor nerve).

One of the most common operations in oculoplastic surgery is the correction of drooping upper eyelids, so your knowledge of the anatomy and function of the levator muscle is critical to your success in oculoplastic surgery. The levator muscle originates at the orbital apex and extends forward inferior to the bone of the orbital roof (Figure 2-20). At the orbital aperture, the levator is supported by Whitnall’s ligament. As the levator muscle travels anteriorly, it becomes a fibrous aponeurosis that extends inferiorly into the eyelid to insert on the anterior aspect of the tarsal plate. Fibrous extensions of the aponeurosis pass through the orbicularis muscle to create the upper eyelid skin crease (Figure 2-21).

Figure 2-20 The levator muscle complex.

Figure 2-21 Cross-section of the upper eyelid.

Whitnall’s ligament

Whitnall’s ligament is an important anatomic landmark. The ligament extends from the fascia surrounding the lacrimal gland temporally to the trochlea medially. Whitnall’s ligament is usually easy to see intraoperatively as a strong white band of fibrous tissue (Figure 2-22). Generally, the tissue superior to the ligament is muscle while the tissue inferior to the ligament is aponeurosis, although variation among individuals exists. It has been suggested that Whitnall’s ligament serves as a “pulley” for the levator muscle. Although the levator muscle complex does not slide through the ligament, the concept of the ligament allowing the muscle to change direction is a helpful one.

Figure 2-22 Whitnall’s ligament.

Müller’s muscle

Müller’s muscle is responsible for the involuntary upper eyelid elevation seen in the sympathetically innervated “fight or flight” phenomenon. Müller’s muscle is “sandwiched” between the conjunctiva posteriorly and the levator aponeurosis anteriorly. Müller’s muscle extends from the superior margin of the upper tarsal plate to the level of Whitnall’s ligament (see Figure 2-21). A prominent surgical landmark on the surface of Müller’s muscle is the peripheral arcade, a vascular arcade extending across the muscle a few millimeters above the tarsal plate (Figure 2-23). The term peripheral arcade is easily confused with the marginal arcade, a vessel that travels on the anterior surface of the tarsus along the lid margin.

Figure 2-23 The peripheral arcade in Müller’s muscle (in this case, with fatty infiltration of Müller’s muscle).

Ptosis of the upper eyelid

Ptosis of the upper eyelid is one of the most commonly encountered clinical problems in oculoplastic surgery. Many causes of ptosis exist. Most cases of upper eyelid ptosis are caused by abnormalities of the levator muscle or aponeurosis. Congenital ptosis (Figure 2-24) results from abnormal development of the levator muscle itself. Intraoperatively, this dystrophy presents as fatty infiltration of an otherwise normal muscle. The most common type of acquired ptosis, involutional ptosis, is generally thought to occur as a result of stretching or thinning of the aponeurosis, rather than of the muscle itself (we will talk more about the etiology of involutional ptosis later; an entire chapter is dedicated to the evaluation and treatment of ptosis). Advancement or tightening of the aponeurosis will elevate the ptotic eyelid in most patients. Loss of sympathetic innervation to Müller’s muscle will cause a mild ptosis of the upper eyelid. This problem is known as Horner’s syndrome.

Figure 2-24 Congenital ptosis of the left upper eyelid. Note that the skin crease is absent. The eyebrows are elevated to help lift the upper eyelid above the pupil.

The frontalis muscle

No doubt you have already seen patients with drooping upper lids who lift their eyebrows to provide a tiny bit more upper eyelid elevation. The frontalis muscle lifts the brows and is a weak retractor of the upper eyelids. The frontalis muscle is a part of the occipitofrontalis musculofascial complex (frontalis muscle, galea aponeurotica, and occipitalis muscle) of the scalp. This broad band of tissue extends across the top of the skull from the occiput to the eyebrows (Figure 2-25). The A in the mnemonic for remembering the layers of the “SCALP” is this aponeurosis (S, scalp, C, subcutaneous tissue, A, aponeurosis, L, loose areolar tissue, P, periosteum.)

Figure 2-25 Frontalis muscle.

The fibrous aponeurosis becomes the frontalis muscle inferior to the hairline. Contraction of the frontalis muscle causes the horizontal furrows in the forehead (Figure 2-26). You may notice that the forehead furrows do not extend to the temporal hairline. The frontalis muscle thins laterally and does not extend to the tail of the brow. The lack of frontalis pull over the tail of the brow explains the temporal brow ptosis seen so commonly in older adults.

Figure 2-26 Forehead furrows form perpendicular to the direction of pull of the frontalis muscle.

Like the other muscles of facial expression, the frontalis muscle is innervated by a branch of the facial nerve. Unlike with other branches of the facial nerve, there is no redundancy in the innervation of the frontalis muscle. A single branch, the frontal nerve (Figure 2-27), innervates the frontalis muscle. The path of the frontal nerve can be estimated by drawing a line from the tragus of the ear to the point 1 cm above the tail of the eyebrow. You will learn to take special care to avoid damage to the frontal nerve during any surgery near the path of the frontal branch. Damage to the nerve may leave the patient with a permanent paresis or paralysis of the frontalis muscle, resulting in a brow ptosis.

Figure 2-27 The path of the frontal branch of the facial nerve.

The lower eyelid retractors

Although we don’t think about the lower eyelid moving much, there are retractors in the lower eyelid as well. The retractors of the lower eyelid are analogous to those of the upper eyelid, but are less well developed. The lower eyelid equivalent to the levator muscle is the capsulopalpebral fascia, which is a band of fibrous tissue that extends from the inferior rectus muscle to the inferior margin of the lower eyelid tarsus (Figure 2-28). As the capsulopalpebral fascia travels anteriorly from the inferior rectus muscle, the fascia splits to surround the inferior oblique muscle. Anterior to the inferior oblique muscle, the fascia reunites as a condensation of fibrous tissue known as Lockwood’s suspensory ligament. This ligament is the equivalent of Whitnall’s ligament in the upper eyelid.

Figure 2-28 Cross-section of the lower eyelid retractors.

The lower eyelid equivalent of Müller’s muscle is known as the inferior tarsal muscle. This poorly developed smooth muscle travels from Lockwood’s ligament to the inferior tarsus between the capsulopalpebral fascia and the conjunctiva. In the lower eyelid, the voluntary and autonomic portions of the retractors are not easily separated during surgery and are known collectively as the lower eyelid retractors.

Involutional entropion

Two clinical examples of problems with the lower eyelid retractors are worth considering. Involutional entropion (turning in of the lower eyelid attributable to aging) is caused by laxity of the lower eyelid retractors. The posterior and inferior pull of the normal retractors into the orbit stabilizes the inferior margin of the tarsus. In combination with other factors, loss of the tension on the tarsus as a result of stretching or “laxity” of the retractors allows the inferior margin of the retractors to rotate upward. The eyelid margin turns inward against the eyeball (Figure 2-29). An operation to tighten the lower eyelid retractors (analogous to correction of upper eyelid ptosis) corrects the entropion.

Figure 2-29 Entropion of the lower eyelid caused by laxity of the lower eyelid retractors.

The preaponeurotic fat

Before we leave this topic, we should cover two other important surgical structures, the preaponeurotic fat and the orbital septum. The preaponeurotic orbital fat (Figure 2-30) is the surgical landmark identifying the levator aponeurosis. Every time you perform ptosis surgery from the skin approach, you will see the orbital fat. In your early experience, you will intentionally identify the fat to help you find the underlying aponeurosis. There are two fat pads that compose the upper eyelid preaponeurotic fat, the central and the medial fat pads. Later, you will learn the terms, intraconal space and extraconal space, regarding compartments in the orbit. For now, keep in mind that the preaponeurotic fat is extraconal fat, or fatty tissue lying outside the muscle cone of the orbit. The central and medial fat pads are enclosed in a thin fibrous capsule with small vessels. The medial fat pad is smaller than the central fat pad and whiter in color. No one knows why this fat is whiter. There is no lateral fat pad in the upper eyelid. The lacrimal gland is in the preaponeurotic space laterally. You will be able to differentiate the lacrimal gland from the fat because the gland is more irregular in texture and is whitish-gray in appearance rather than yellow. The fat itself is relatively avascular, whereas the lacrimal gland is well vascularized.

Figure 2-30 The preaponeurotic fat.

As in the upper eyelid, identification of the fat pads is the key to identifying the lower eyelid retractors. In the lower eyelids, there are three fat pads: the medial, central, and lateral fat pads (see Figure 2-30). As you would expect, these fat pads are found posterior to the orbital septum and anterior to the lower eyelid retractors. Prolapse, or bulging of the lower eyelid fat pads, is a common cosmetic concern. The main goal of the lower eyelid blepharoplasty operation is to eliminate this prolapse.

The orbital septum

Anterior to the preaponeurotic fat is a tough fibrous layer that extends from the orbital rims to the tarsal plates known as the orbital septum (Figure 2-31). The septum is the anatomic boundary between the eyelids and the orbit, lying between the orbicularis muscle and the orbital fat. Fat seen in an eyelid laceration means that the septum has been cut and that deeper tissues, including the eye or even the brain, may be injured. An intact septum means that there has been no penetration into the orbit from the anterior aspect. Infections of the eyelid are prevented from extending posteriorly by the orbital septum. As well as preventing infection from spreading posteriorly, the septum prevents the orbital contents from bulging anteriorly. As we discussed earlier, with age, the septum thins and the orbital fat prolapses forward, accounting for some of the fullness seen in the upper and lower eyelids of adults (Figure 2-32). You will notice this difference in the thickness of the septum in pediatric and adult eyelid operations.

Figure 2-31 The orbital septum.

Figure 2-32 Upper eyelid fat prolapse caused by thinning of the orbital septum. Note the prominent upper eyelid nasal fat pad.

You will see the septum often in eyelid surgery. The eyelid incisions that you will make for ptosis correction typically start with an incision through the skin and then a cut through the orbicularis muscle to the level of the orbital septum. Once the septum is exposed, you will open the septum to expose the preaponeurotic fat, your landmark for the aponeurosis. The attachment of the origin of the septum along the orbital rim is called the arcus marginalis

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The Diagnosis and Management of Misdirected Eyelashes The Art of the Surgical Technique Aesthetic Surgery of the Face Evaluation and Treatment of the Patient with Ptosis Surgical Approaches to the Orbit Diagnosis of Malignant and Benign Lid Lesions Made Easy

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