• External Landmarks

Some people think of themselves as having only one "eyelid." Actually, we 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 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

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 six muscles that move each eyeball are called the extraocular muscles and are not particularly pertinent to eyelid surgery, except for one of the smallest. The inferior oblique muscle may be encountered during the removal of lower eyelid fat.

• The Eyelid Support System

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.

• Eyelid Fat

If the orbital septum is stripped away (again, mind you, only for the purposes of this discussion), the eyelid fat will be exposed in all its glory. The upper eyelid fat lies just in front of the levator aponeurosis (recall, the tendon from the upper eyelid's main opening muscle).

The upper eyelid fat may be thought of as consisting of two pockets: a long thin middle fat pocket and a globular nasal fat pocket.

The lower eyelid fat may be thought of as consisting of three pockets, called the nasal, middle, and temporal fat pockets.

Eyelid fat is really an extension of the same orbital fat that fills the entire socket.

• The Deeper Eyelid

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.

• Socket

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.

Bone has a thin but strong outer lining called periosteum, which is put to good use in some variations of advanced blepharoplasty.

• The Midface

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 rather complicated names. For that reason, we will refer to them as the soft tissues of the midface.