The Supraorbital Margin of Japanese Who Have No Visible Superior Palpebral Crease and Persistently Lift the Eyebrow in Primary Gaze Is Higher and More Obtuse Than Those Who Do Not

Yoshito Mishima, MD; Kiyoshi Matsuo, MD, PhD; Shunsuke Yuzuriha, MD, PhD; Ai Kaneko, MD

Disclosures

ePlasty. 2013;13 

In This Article

Discussion

According to our evaluation of the coronal shape of the supraorbital margin using VD/HD, the supraorbital margin of 10 subjects without visible SPC who persistently lifted the eyebrow in primary gaze was significantly higher than that of 13 subjects with visible SPC who did not, even though the vertical palpebral fissure of the former appeared to be narrower. The relative height of the supraorbital margin appears not to be consistent with the vertical palpebral fissure, but rather with the height of the persistently lifted eyebrow. According to our analysis of the relationship between the coronal and sagittal shapes of the supraorbital margin, the relative coronal height significantly correlated to the obtuseness of the sagittal angle of the supraorbital margin among all subjects. These results suggest that the persistently lifted eyebrow due to the presence of tonic reflex contraction of the frontalis muscle in primary gaze may functionally lift the soft tissues around the supraorbital margin to mechanically apply pressure to the supraorbital margin, resulting in creation of characteristically high (round) and obtuse supraorbital margin in the subjects without visible SPC.

To explain the anatomical discrepancy between the vertical palpebral fissure and the relative height of the supraorbital margin of the 2 groups, Baba et al[4] hypothesized that the facial flatness and narrow eye in Yayoi migrants for cold tolerance caused the brain to become larger and/or move anteriorly and enlargement of the maxillary sinus. Consequently, the face became extended in the vertical plane, resulting in a flat face. The supraorbital region shows a flat nasion and frontal sinus as well as a round supraorbital margin. However, it seems controversial that the round supraorbital margin, which more greatly exposes the orbital contents to the open air, is considered to be an adaptation to cold exposure, although since anthropological studies depended on skeletons and bones, they could not evaluate eyebrow movement due to tonic reflex contraction of the frontalis muscle as well as the presence of SPC.

The bones and articulations of the craniofacial skeleton grow and function in an environment of mechanical forces. These forces, which include muscle activity, mastication, the expansile growth of the brain, gravity, and man-made orthodontic appliances, influence the shape and relative position of each bone in the complex through the process of biological adaptation termed remodeling.[22–24] For instance, orthodontic tooth movement is dependent on the remodeling of the periodontal ligament and alveolar bone by mechanical means,[24,25] and the temporomandibular joint can be remodeled by Herbst treatment,[26] wherein an increase in mandibular prognathism in both adolescents and young adults seems, in particular, to be a result of condylar and glenoid fossa remodeling. Furthermore, masseter muscle hypertrophy was reported to frequently accompany bone thickening in the region of the mandibular angle, even in unilateral cases;[27] the hyperostotic change was thought to be a secondary phenomenon to the mechanical stretching of the region of the mandibular angle by contraction of the masseter muscle. These reports suggest a possibility that the shape of the supraorbital margin may too be subject to remodeling by the mechanical force of the persistently lifted eyebrow by tonic contraction of the frontalis muscle in primary gaze.

Although we have proven an association between higher and more obtuse supraorbital margins in the group of subjects who had no visible SPC and persistently lifted the eyebrows, the cause of this relationship remains unclear and is only hypothesis driven. To prove causal relationship, Jomon Japanese or European patients with severe unilateral congenital ptosis, who persistently lift the eyebrow on the ptotic side and do not on the nonptotic side, should be evaluated. Because the small numbers of subjects were studied in the 2 groups to prove our hypothesis based on the anthropological discrepancy, a power analysis should be performed to determine the numbers required to prove or refute our hypothesis.

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