Anatomy seems to be an inherently boring subject that rarely becomes "unbelievably interesting" to anyone other than anatomists, surgeons, and the occasional determined patient trying to figure out what went wrong. Still, without at least a working knowledge of eyelid anatomy basics, you won't be able to fully benefit from later discussions in this course. Not that you have to memorize all the technical terms that follow. Just remember where you saw them and that you can always come back for a quick refresher.
Far from just "a piece of skin covering the eye," the eyelid is one of the most complex structures in the body. Composed of multiple main layers with intricate connections, it's a remarkable tiny organ assigned a protective function far more important than "looking good."
To understand why perfectly healthy eyelids on one person can sometimes appear so different from those on another healthy person, you first have to learn the basic anatomy of not only the eyelid itself but also of the structures located immediately above, below, and behind the eye.
Likewise, to understand why some of the "beauty" of a youthful eyelid tends to fade over time, you also need to learn about the changing anatomical relationships and interactions between the lid, orbital, and surrounding periorbital tissues.
If you find yourself intimidated or bored by what may sound like technical minutiae, do consider this. Not until you've mastered at least the essentials of eyelid anatomy and physiology will you be able to evaluate the soundness (or lack thereof) or safety (or lack thereof) of the many disparate cosmetic procedures that now purport to restore aging lids to their once former glory. So, here we go . . .
|A||Medial Commissure||Inner corner where eyelids join|
|B||Lateral Commissure||Outer corner where eyelids join|
|C||Medial Canthus||Tissues just beyond medial commissure|
|D||Lateral Canthus||Tissues just beyond lateral commissure|
|E||Upper Eyelid Crease||Indentation or fold in upper eyelid|
|F||Lower Eyelid Margin||Edge of eyelid|
|G||Nasojugal Fold||Indentation extending from lid down along nose|
|H||Sclera||White layer of eyeball|
|I||Iris||Colored layer inside of eyeball|
|J||Pupil||Hole in iris that lets in light|
|K||Palpebral Fissure||(Not labeled) Opening between the eyelids|
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Many people think of themselves as having only one "eyelid" when we really all have two (or four, if you count both sides). The one that moves over the eyeball surface like a windshield wiper is called the upper eyelid. The one that sits below the eye is called --what else?--the lower eyelid. Anatomically speaking, the two are almost mirror images of one another.
The edge of either eyelid (the junction where the front and back sides join together) is called the eyelid margin. The eyelashes are located on the most forward edge of the lid margin.
The palpebral fissure is that empty space between the upper and lower eyelid margins when the eyelids are open (that is, the space between the eyelids that allows you to see your eyeball and your eyeball to see the world).
The points at which the upper and lower eyelids fuse together are called the commissures. The medial commissure is that point nearest the nose. The lateral commissure is on the other side closest to the temple.
The tiny openings to the tear drainage system are called the lacrimal puncta (singular: punctum) and are located on the eyelid margin just before the medial commissure.
The areas of "soft tissue" (skin, muscle, tendons, and fat) just beyond the commissures are called the canthi (the singular form of canthi is canthus). The medial canthus starts at the medial commissure and extends about 1/2 inch towards the nose. The lateral canthus starts at the lateral commissure and extends about 1/2 inch towards the temple.
The upper eyelid crease in the indentation extending across the upper eyelid. The crease may be poorly formed or even absent in many Asian patients.
Pertinent Muscles of the Eyelid, Brow, and Face
|A||Orbicularis Muscle (palpebral)||Eyelid closing muscle|
|B||Orbicularis Muscle (orbital)||Eyelid closing muscle|
|C||Frontalis Muscle||Forehead muscle|
|D||Procerus Muscle||Muscle that lowers brows|
|E||Corrugator Muscle||Muscle that brings brows together|
|F||Midfacial Muscles||Muscles of the cheek|
|G||Malar Fat Pad||Large cheek fat pad|
|H||Suborbicularis Fat (SOOF)||Fat pad beneath orbicularis muscle|
|I||Temporalis Muscle & Fascia||Muscle of temple|
The muscle that closes the eyelids is called the orbicularis muscle. It's a large muscle that widely encircles each eye.
The main muscle that opens the eyelids is called the levator muscle. The levator muscle actually starts off deep in the socket, extends up over the top of the eye, and then turns into a tendon (called the levator aponeurosis) as it connects to the eyelid itself.
The muscle of the forehead that pulls up the eyebrows and caused forehead wrinkling is called the frontalis muscle.
The nasal muscles that pull the skin between the eyebrows down causing horizontal wrinkles are called the procerus muscles.
The nasal muscles that push the skin between the eyebrows into vertical folds are called the corrugator muscles.
The Eyelid Support System
|A||Orbital Septum||Layer holding back orbital fat|
|B||Levator Aponeurosis||Eyelid muscle tendon seen through septum|
Deeper Eyelid and Anterior Orbit
(orbital septum removed)
|A||Medial Canthal Tendon||Tendon anchoring lids to bone|
|B||Lateral Canthal Tendon||Tendon anchoring lids to bone|
|C||Upper Tarsus (Tarsal Plate)||Stiffening element (like cartilage)|
|D||Lower Tarsus (Tarsal Plate)||Stiffening element (like cartilage)|
|E||Levator Muscle (cut off at tendon)||Main opening muscle of upper lid|
|F||Superior Oblique Tendon||Tendon of muscle moving eyeball|
|G||Inferior Oblique Muscle||Muscle moving eyeball|
|H||Lacrimal Gland (Tear Gland)||Gland that produces watery tears|
|I||Lacrimal Sac (Tear Sac)||Part of tear drainage system|
|J||Fat||Orbital fat extending into eyelids|
|K||Orbital Rim||Rim of socket bone|
If, for the purposes of this discussion, the skin and orbicularis muscles of the eyelids are removed, the main structural support system of the eyelid is exposed. This system is important in understanding the cause of eyelid deterioration and the operations designed to restore a more youthful appearance.
The easiest way to think of the lower lid support system is to imagine a hammock hanging between two trees. The equivalent of the main body of the hammock would be a thin cartilage-like structure that gives shape to the eyelid and is known as the tarsus or tarsal plate.
The tarsal plate is connected to the orbital rim of bone (the two trees) by a tendon on each side (the connecting ends of the hammock), known as the medial canthal tendon (on the side towards the nose) and the lateral canthal tendon (on the side towards the temple).
A similar basic support system exists in the upper lid, although the "hammock analogy" is a little harder to visualize. Just for your information, the system of support described above is known more formally as the tarsoligamentous sling.
The orbital septum is a fibrous membrane that can be thought of as holding back the fat that fills the socket and cushions the eyeball. In the lower eyelid, the orbital septum connects to the tarsoligamentous and extends all the way to rim of bone beneath the eye. In the upper lid, the orbital septum connects very near the top of the tarsal plate and extends all the way to the rim of bone above the eye.
Muscles of the Eyeball
The six muscles that move the eyeball are called the extraocular muscles and are not particularly pertinent to eyelid surgery, except for one. The inferior oblique muscle may be encountered during the removal of lower eyelid fat. If damaged, double vision may result.
|Bright red||Superior Rectus|
|Light blue||Medial Rectus|
|Dark blue||Inferior Oblique|
|Brick red||(Levator Muscle)|
If the orbital septum is stripped away (again, mind you, only for the purposes of this discussion), the fat in the eyelid will be exposed in all its glory. This fat coming forward from the deeper orbit fat lies just in front of the levator aponeurosis (recall, the tendon from the upper eyelid's main opening muscle).
The upper orbital fat may be thought of as consisting of two pockets: a long thin middle fat pocket and a globular nasal fat pocket.
The lower orbital fat may be thought of as consisting of three pockets, called the nasal, middle, and temporal fat pockets.
Why do we call it "orbital fat" instead of "eyelid fat"? The fat inflating the eyelids is really an extension of the same orbital fat that fills up the entire socket.
The Deeper Eyelid
Lower Eyelid in Cross-Section
|B||Skin||Epidermis on surface, dermis below|
|C||Orbicularis Muscle||Eyelid closing muscle|
|D||Tarsus (Tarsal Plate)||Stiffening element (like cartilage)|
|E||Orbital Septum||Layer holding back the orbital fat|
|F||Orbital Fat||Fat from the socket extending into lid|
|G||Inferior Oblique Muscle||Muscle moving the eyeball|
|H||Lower Eyelid Retractors||Structures that move the lid downward|
|I||Orbital Bone||Bone surrounding the eye; socket|
|J||Conjunctiva||Lining of the back of eyelid and front of eye|
|K||Periosteum||Lining of the bone (called 'periorbita' in orbit)|
Upper Eyelid in Cross-Section
As mentioned earlier, the eyelid fat sits just in front of the tendons of the main opening muscles and tendons (known also as the "retractors") of the eyelids.
The main opening muscle/tendon system in the upper eyelid is, as noted above, the levator muscle and aponeurosis. Small strands of tissue extending from the levator aponeurosis help to create the upper eyelid crease.
The main opening muscle/tendon system in the lower eyelid (yes, the lower lid moves a little, too) is called the capsulopalpebral fascia, which is a term we will try to use sparingly if at all.
The deepest layers of the upper eyelid consist of a minor retractor muscle (Müller's muscle) that is not very important in blepharoplasty. The back lining of the eyelids is known as the conjunctiva.
This section is a breeze. Suffice it to say that the eyeball is cushioned inside of a protective socket of bone, the rim of which is known as the orbital rim (orbital bones shown in illustration above labeled "Muscles of the Eyeball."
Bone has a thin but strong outer lining called periosteum, which is put to good use in some variations of advanced blepharoplasty.
(illustration of muscles near top)
The tissues of the midface begin with the cheek and are thus not "formally" part of the eyelid. However, since the lower eyelid and cheek combine to form a single functional unit, the mention of several structures of relevance follows.
The suborbicularis oculi fat (SOOF) is a layer of fat located just beneath the lowest part of the orbicularis muscle of the lower eyelid. You'll find out later why it's important.
The malar fat pad is a larger layer of cheek fat starting just below the orbital rim of bone.
The numerous muscles of the midface, as well as their fibrous support system and surrounding fat pockets, have complicated names that are tongue-twisters to say the least. For that reason, we will refer to them as the soft tissues of the midface and leave it at that.
* * *
Congratulations! You are now an expert in eyelid anatomy. In later chapters, all of what you just learned will be used and reviewed as different surgical procedures are presented and discussed.
If, instead, you found the discussion too technical and simply skipped to the end to continue to the next topic, try the following video.