This chapter deals with the author’s concept of the natural biodynamic of the eyelid layers, the importance of fat within the eyelid’s preaponeurotic space, its facilitation and hindrance of the natural eye opening mechanism ( Figure 17-1 ).
Classically, the normal eyelid anatomy can be conceptualized as consisting of two layers: the anterior skin/orbicularis oculi muscle layer and the posterior layers of the levator muscle and aponeurosis, Müller’s muscle and the tarsal plate.
In general, Caucasian eyelids with a crease are thinner than those of their Asian counterparts. This is attributable to a combination of factors that include a higher point of fusion of the orbital septum onto the levator aponeurosis, the relatively higher position of preaponeurotic fat pads and the resultant thinner lower segment of eyelid, less preseptal fat and thinner orbicularis. Comparatively, Caucasians with an eyelid crease possess a greater number of distal fibers of the levator aponeurosis that terminate toward the skin along the superior tarsal border and the area above it to form the eyelid crease. When the levator contracts, the tarsal plate vectors upward and the eyelid crease invaginates easily. Caucasians may often have a deep-set supratarsal sulcus ( Figure 17-2 ).
In Asians who are born with a natural crease, although the eyelid may still be thicker than in Caucasians with an upper lid crease, there are distal fibers of the levator aponeurosis terminating toward the skin along the superior tarsal border. Despite the low point of fusion of the orbital septum, when the levator contracts, there is an invagination of skin along the superior tarsal margin to form a clinically apparent upper eyelid crease. When the lids are open and the subject is looking ahead, there is a greater degree of fullness in the preseptal region compared with a Caucasian with a crease, but less than that which is typically seen in Asians without an upper lid crease ( Figure 17-3 ).
Asians who are without an eyelid crease typically have thicker eyelids because of the presence of a hypertrophied orbicularis and the presence of fat in the pretarsal, preseptal and preaponeurotic areas. The orbital septum fuses with the levator aponeurosis at a lower point compared with those Caucasians with an upper eyelid crease. There are relatively few fibers or no attachment from the levator aponeurosis toward the skin along the superior tarsal border. Their pretarsal and preseptal zones are thicker compared with Caucasians or Asians who have an eyelid crease ( Figure 17-4 ).
In aesthetic Asian blepharoplasty, where the goal has always been to create an ethnically appropriate crease, there are two categories of methods used to achieve this goal. The first consists of the suture ligation methods, which are often described as being less invasive and simpler to perform, and use several buried sutures to tighten the soft tissues along the superior tarsal border, which includes orbicularis, levator aponeurosis and Müller’s muscle. The other category is the external incisional approach, whereby a skin incision is made along the designed crease and varying amounts of skin, muscle and soft tissues may be removed; this is then coupled with various methods of crease construction by means of fixation or attachment of skin to the levator aponeurosis, skin to the tarsus, or orbicularis to aponeurosis fixation.
The surgical results often depend on a complex interaction between the degree of excessive tissue overlying the pretarsal and preseptal areas, the presence of fat, the thickness of skin over each of the two areas mentioned above, the position of the globe, the brow position, levator function and whether there is a firm adhesion of skin to orbicularis in the pretarsal area. In a normal upper eyelid, when the eyes are looking straight ahead and the lids are open, the anterior layer is in passive relaxation, allowing the posterior levator/Müller’s muscle/tarsus to actively contract and pull the lid margin upward into an open position. The posterior layer only has to retract (glide) up and inward for 2–4 mm relative to the anterior layer for a reasonable crease to be observed. The vertical span (in millimeters) of the eyelid fold overhanging the crease can be measured simply by subtracting the ‘observed crease height’ (from eyelash to inferior border of eyelid fold) from the anatomical crease height (measured with the lid fold retracted away to expose the true crease line). (In Advanced: Chapter 20 , we can say
Dimension of the fold = Tilted crease height − Apparent crease height .