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ANATOMY

The anatomy of the eyelids is complex with several layers which require attention during surgery. The layers consist of an external layer, the anterior lamella, and an internal layer, the posterior lamella. The anterior lamella is made up primarily of skin and muscle. The layer of muscle in the exterior layer is the orbicularis oculi muscle which is a flat ring of thin muscle that circles the upper and lower eyelids.

This is the muscle which creates blinking and closure of the eyelids, not movement of the eyeball. The posterior lamella is made up of the support structures of the eyelids. The tarsal plate, in the upper lid, and the tarsus, in the lower lid, are connected to the bone around the eye, the orbit, by ligaments. The septum is a thin membrane which separates the anterior and posterior lamellae and contains the perirobital fat pads, the fat around the eye.

This varies from individual to individual as well as between sexes and ethnic background. The fold above the crease which makes the eyes appear droopy or tired is made up of skin, muscle , and fat. The dark circles and puffiness below the eyes is often caused by a combination of loose skin and muscle as well as excess fat. The common terminology used to describe this condition is dermatochalasis.

Posterior Lamella
The shape and position of the eyelids are related to changes in the internal layer of the eyelids. The normal position of the upper eyelid is halfway between the pupil and the top of the iris, the colored part of the eye. A droopy upper eyelid can occur from looseness or laxity of the muscle that is responsible for keeping the upper eyelid open, the levator palpebrae muscle. The term used to describe this condition is ptosis.

The normal position for the lower lid is just at the bottom of the iris. A droopy lower lid can occur from laxity of the ligaments which hold the lid up and from scarring of the lower lid retractors. The term used to describe a droopy lower lid with the white part of the eye showing between the lid and iris is scleral show. When the droopy eyelid also turns outward, this is called an ectropion. When the droopy eyelid turns inward, this is called an entropion.

Orbicularis Oculi Muscle
The orbicularis oculi muscle is a thin layer of muscle which has a primary function to close the eyelids. The ring of muscles circle the eye and extends upward to the eyebrow and downward to the cheek. There are three main divisions of the muscle with different functions: the pretarsal orbicularis, the preseptal orbicularis, and the orbital orbicularis. The pretarsal muscle causes an involuntary blink and helps with drainage of the tears. The preseptal muscle causes the voluntary blink , the intentional closure of the eyelids. The orbital muscle causes squinting and protection of the eye by squeezing the lids closed.

The pretarsal muscle causes an involuntary blink and helps with drainage of the tears. The preseptal muscle causes the voluntary blink , the intentional closure of the eyelids. The orbital muscle causes squinting and protection of the eye by squeezing the lids closed.

Periorbital Fat Pads
The fat pads which surround the eye and contribute to the puffy appearance of the eyes are the periorbital fat pads. There are two pads in the upper lid and three pads in the lower lid.

The upper lid pads are called the nasal and central fat pads, and the lower lid pads are nasal, central, and lateral. These pads are extensions of deeper orbital fat which surrounds the eye socket and are only partially removed during blepharoplasty.

Midface Fat Pads
There are two additional fat pads below the periorbital fat which contribute to the aging appearance of the eyes and mid-section of the face. The fat layer just below the orbicularis muscle is the sub-orbicularis oculi fat or SOOF. The fat component of the cheek is the malar fat pad. Both of these fat pads sag with age which make the cheekbones look smaller and create lines between the nose and the upper lip, the nasolabial fold.

Lateral Canthus
The lateral canthus is located at the outer corner of the eyelid and connects the eyelid to the bone. The lateral canthus is part of the posterior lamella and is an important support structure for the eyelid. The lateral canthal ligament holds the lower lid in position. When laxity of the support structures occurs, the lower lid can become droopy.

Correction of a droopy lower lid often requires tightening of the lateral canthus. The lateral canthus is tightened by two main techniques. A lateral canthopexy is used to correct minimal laxity by suturing the lateral canathus and lateral retinaculum to the bone at the corner of the eye. A lateral canthoplasty is used to correct more significant laxity with a tiny incision at the corner of the eyelid by suturing the tarsus to the bone.