The preseptal fat occurs mainly outside the orbital rim on the lower lateral brow and upper malar areas. Superiorly, this fat is positioned deep to orbicularis and frontalis, extending over the brow onto the surface of the adjacent septum orbitale of the upper lid. This 'brow fat pad of Charpy' has more recently been termed the retro-orbicularis oculi fat (ROOF)1' and the lid part as the preseptal fat pad. It can be up to 6 mm thick as it passes over the rim, tapering as it descends toward the lid margin to terminate where the fibers of the septum orbitale fuse with the fascia on the under-surface of orbicularis just millimeters above the supra-tarsal crease. Aesthetically, the ROOF provides fullness and projection for the brow and the preseptal component contributes to the supratarsal fold fullness. The equivalent layer inferiorly is the sub-orbicularis oculi fat (SOOF), which differs in being thinner and it usually does not cross the orbital margin into the lid. The SOOF is discussed in the midcheek anatomy section.
The postseptal fat is conventionally divided into compartments: two (medial and central fat pads) in the upper lid and three (medial, central and lateral fat pads) in the lower lid. These compartments are made up of fat extensions from the adipose body of the orbit except for the upper lid central fat pad, which is separate preaponeurotic fat. The two types of fat differ in their color and consistency, however all the fat is linked by interconnecting septa that transgress the intrinsic muscle cone. Hence traction on fat just posterior to the septum orbitale can produce forces in the posterior extraconal and even intraconal and peri-optic nerve region.
The adipose body of the orbit is pale yellow and fills the orbital cavity, reaching the septum orbitale anteriorly. It has a central portion included in the cone of intrinsic muscle around the optic nerve (intraconal) and extensions coming out of the cone to reach the orbital walls through the orifices between the muscles (extraconal). As this fat reaches the septum orbitale it is divided into compartments by structures within the anterior orbit. Thus inferomedially the fat passes either side of the inferior oblique muscle to appear as the medial and central compartments of the lower lid. Inferolaterally the arcuate expansion of the capsulo-palpebral fascia separates the central from the lateral compartment.
In the upper lid, the fat of the adipose body only reaches the septum orbitale superomedially, where it extends forward as the medial fat pad. The preaponeurotic fat, which is the central fat pad encountered in blepharoplasty, appears to be a different type of fat and perhaps separate from the adipose body of the orbit. It is deep yellow in color and is the most cepha-lad fat compartment. It is located under the orbital roof and lies on the levator aponeurosis, in contact with the septum orbitale. It is usually limited medially by a fibrous septum containing the reflected tendon of the superior oblique muscle, separating it from the medial compartment. With aging changes, a medial herniation of the central fat pad occasionally develops and comes to overlie the true medial fat pad. Judicious adjustment of this fat extension may be required during upper lid blepharoplasty. A lateral extension of the preaponeurotic fat is always present behind the lacrimal gland, and in many older patients it protrudes anteriorly beyond the inferior border of the lacrimal gland becoming clinically apparent.18 The individual appearance of upper lid fullness is determined by the summation of the volume and precise location of both the preaponeurotic fat and the preseptal fat.
Eisler's fat pad is a small pocket of fat situated between the orbital septum anteriorly and the lateral canthal tendon posteriorly. It is inferior to the lateral extension of the preaponeurotic fat and is not encountered during standard blepharoplasty. It is however useful as a landmark for Whitnall's tubercle during canthoplasty.
No comments:
Post a Comment