Vector-Calibrated Incisional Technique (VCIT)
VCIT is the latest and most advanced technique for incision double eyelid surgery.
It was devised and is currently performed by Dr. Kenneth Kim, of Dream Medical Group, and other select surgeons in South Korea. This method has been gaining popularity in the Korean media and is considered to be a specialty in double eyelid surgery. This technique is unique in that it makes use of the septo-aponeurosis junctional thickening, a connective tissue in the eyelid. The septo-aponeurosis junctional thickening is comprised of the distal aspect of the levator and a thin layer of tissue that encases the eyelid fat. The identity of the septo-aponeurosis junctional thickening has been controversial among surgeons, mainly for the subtle role it plays and difficulty in locating it; it has often been simply known as a distal part of the levator. Despite its subtle and delicate nature, a selective group of surgeons found it had advantages as a base for suture anchorage through extensive research.
(A) Side view of eyelid before operation; (B) low fixation; (C) high fixation; (D) conjoined septo-aponeurosis junctional thickening fixation.
As observed in (B) and (C), neither the tarsus nor the levator aponeurosis stretches toward the suture to minimize depth. This lack of elasticity/recoil effect causes a static appearance in the crease for tarsus fixation and deep crease for levator fixation. However, in (D), the septo-aponeurosis junctional thickening (gray) has stretched toward the suture, as compared to pre-operation in (A), reducing unnecessary depth and resulting in a dynamic crease that moves with the eyelid’s natural movements.
In performing VCIT, the septo-levator complex must be meticulously uncovered – its position is challenging to locate as it is hidden by layers of soft tissue. Because the septo-levator complex is located at a more superficial level than the levator aponeurosis, the sutures fasten to a thinner layer of tissue resulting in less depth penetration. Furthermore, due to the higher resilience and flexibility of the septo-levator complex, fixation to this area accommodates for any extra depth by virtue of its elastic attributes, much like a rubber band. This results in a softer, gentler crease depth, which more closely resembles a natural double eyelid in both appearance and movement.
In performing VCIT, the septo-aponeurosis junctional thickening must be meticulously uncovered – its position is challenging to locate as it is hidden by layers of soft tissue.
Because the septo-aponeurosis junctional thickening is located at a more superficial level than the levator aponeurosis, the sutures fasten to a thinner layer of tissue resulting in less depth penetration. Furthermore, due to the higher resilience and flexibility of the septo-aponeurosis junctional thickening, fixation to this area accommodates for any extra depth by virtue of its elastic attributes, much like a rubber band. This results in a softer, gentler crease depth, which more closely resembles a natural double eyelid in both appearance and movement.
Suture fixation at the septo-aponeurosis junctional.
The left image depicts the eyelid before surgery. The right image depicts post-operation of the sutures fixed at the septo-aponeurosis junctional thickening (shown in gray). Note the difference in shape of the conjoined between pre-operation and post-operation – the conjoined has stretched to accommodate the extra tension from the sutures, adding to the dynamicity of a crease formed by VCIT.
This new open technique takes advantage of much more than an alternate eyelid tissue–it utilizes biomechanics to find the ultimate balance. Many factors apply in finding this balance: determination of the crease height, amount of skin, fat, and other soft tissue to be excised, how much tightening is needed in the eye-elevating muscles, and the vector-calibrated length of the septo-aponeurosis junctional thickening. The new incision technique is appropriately named “Vector-Calibrated” because it applies clinical scientific knowledge in biomechanics to achieve the ideal aesthetic and functional balance in the eyelid. It differs significantly from prior techniques in that it does not arbitrarily create a crease at any desired height, but aims for calculated results that complement the entire eye.
SIMPLIFIED ANALYSIS OF THE EYELID
The length between points 1 and 2 is the distance that the skin is displaced when it attaches to the septo-aponeurotic junctional thickening (SAJT). Refer to the dashed line as the “line of attachment.” The line of attachment between points 1 and 2’ represents the crease that forms when the eyes open. The SAJT acts as a hinge between the skin and levator aponeurosis. It stretches to its full length – which has been altered – to accommodate for the extra distance that the skin would normally cover. Thus, the distance between points 1 and 2’ is minimized with the use of the SAJT.
COMPARING DIFFERENT EYELID THICKNESSES
The spring constant for the spring model mainly depends on the thickness of the skin. The thicker the skin, the more resistant it is to external forces; therefore, the spring constant increases with thicker skin.
kthick > kthin
Note the skin stretching represented by the red arrow.
Notice that x1 > x2. The length of the septo-aponeurosis junctional thickening (SAJT) also changes depending on the thickness of the skin. The thicker the skin, the shorter the length of SAJT. Conversely, note that d2 > d1, since thicker skin must be stretched to attach to the SAJT.
FREE BODY DIAGRAM ANALYSIS
Thicker skin requires a greater pulling force (Fthick) than does thin skin for the formation of a crisp crease line. According to Hooke’s Law, this implies a greater displacement distance in the spring model. Thus, d2 > d1. Recall that kthick > kthin. Comparing the skin’s resistive forces,
Fthick = kthick • d2
Fthick = kthick • d1
Fthick > Fthin
Displacement distance is determined by length of the septo-aponeurosis junctional thickening. To have d2 > d1, we need x1 > x2.
Before skin is attached, spring is not compressed nor stretched, with spring constant k1. Note that thicker skin has higher resistance, and thus a higher k value in its model. After attachment: spring is stretched, with spring constant k1. Using Hooke’s Law,
Fspring = -k • d
where k is the spring constant, and d the spring’s displacement, the force experienced by the skin is equivalent to the resistance of the spring, which is
Fskin = -kskin • d
As the eyes open, the muscle fibers in the levator aponeurosis move upwards, stretching the spring even more relative to its position when the eyes are closed. The skin experiences an increased pull when the eye opens, as observed,
Fskin = -kskin • d / cos θ
where cos θ< 1, maximizing the pull on the skin. Note that a higher angle of elevation corresponds to increased force.
The increased force on the skin causes the crease to form:
- Higher on the eyelid due to the movement of the levator aponeurosis
- Deeper towards the levator aponeurosis due to increased displacement represented
THE SKIN: EYES CLOSED
Before skin is attached, spring is not compressed nor stretched with spring constant k1. Note that thicker skin has higher resistance, and thus a higher k value in its model. After attachment, the skin stretches. Spring is stretched, with spring constant k1.
Using Hooke’s Law,
Fspring = -k • d
Where k is the spring constant, and d the spring’s displacement. The force experienced by the skin is equivalent to the resistance of the spring, which is
Fskin = -kskin • d
The eyelid skin is modeled as an elastic spring. The skin’s elasticity is represented by spring constant kthin, which is used to determine how much force the skin experiences when it stretches.