Superior Palpebral Crease and Eyebrow Height of Japanese

Abstract and Introduction

Abstract

Objective: Anthropological studies divided the Japanese into the Yayoi migrants, who had narrow eye, no visible superior palpebral crease, and high-positioned round supraorbital margins for cold tolerance, and the Jomon natives, who had wide eye, visible superior palpebral crease, and low-positioned straight supraorbital margins, thus suggesting an anatomical discrepancy between the vertical palpebral fissure and the height of the supraorbital margin. Because Japanese subjects without visible superior palpebral crease open their eyelids by lifting the eyebrows with the anterior lamella owing to increased tonic contraction of the frontalis muscle, we hypothesized that persistently lifting the eyebrows in primary gaze mechanically remodels the supraorbital margin to be high positioned and round.

Method: We evaluated whether subjects without visible superior palpebral crease persistently lifted their eyelids more than subjects with visible superior palpebral crease, whether the presence of persistently lifted eyebrow in primary gaze affected the relative height of the supraorbital margin in coronal view 3-dimensional computed tomography imaging, and whether the shape of the supraorbital margin in the coronal view affected that in the sagittal view 3-dimensional computed tomography imaging.

Results: Eyebrow height in subjects without visible superior palpebral crease was significantly larger than that in subjects with visible superior palpebral crease. The supraorbital margin of subjects without visible superior palpebral crease who persistently lifted the eyebrows in primary gaze was higher (rounder) and more obtuse than that of Japanese subjects with visible superior palpebral crease who did not.

Conclusions: The mechanical pressure applied to the supraorbital margin by persistently lifting the eyebrows appears to functionally, rather than genetically, create the high (round) and obtuse supraorbital margin.

Introduction

According to anthropological studies, the Japanese are genetically divided into the Neolithic Jomon natives and the Bronze Yayoi migrants from the cold Asian continent.^[1–6] The Yayoi migrants were reported to possess eyelid structures for cold tolerance, such as narrow eye, no visible superior palpebral crease (SPC), and high-positioned round supraorbital margin (Figs 1a, 2b, and 3a), whereas the Jomon natives were reported to have features of wide eye, visible SPC, and low-positioned straight supraorbital margin (Figs 1b, 2d, 2f, and 3b). However, there is an anatomical discrepancy between the vertical palpebral fissure and the height of the supraorbital margin; the narrow-eyed Yayoi migrants have higher-positioned round supraorbital margins, whereas the wide-eyed Jomon natives have lower-positioned straight supraorbital margins.

(Enlarge Image)

Figure 1.

Anatomy and neurophysiology related to eyelid opening. (a) Subjects without visible superior palpebral crease (SPC) or Jomon natives. (b) Subjects with visible SPC or Yayoi migrants. ? indicates unknown nucleus; III CCN, central caudal nucleus of the oculomotor nuclear complex; FAST, fast-twitch muscle fibers; FEF, frontal eye field; LTL, lower-positioned transverse ligament; mesV, mesencephalic trigeminal nucleus; PHASIC, phasic contraction; PMN, premotor neurons in the rostral interstitial nucleus of the medial longitudinal fasciculus; REF, reflex contraction; SLOW, slow-twitch muscle fibers; TONIC, tonic contraction; VII FM, frontalis motor neurons; VOL, voluntary contraction; W, Whitnall's ligament.

(Enlarge Image)

Figure 2.

Digital immobilization of the eyebrow movement during eyelid opening classifies subjects as being without or with visible SPC as well as being with or without persistent lifting of the eyebrows in primary gaze. (a-c) A 25-year-old subject without visible SPC who did not have blepharoptosis but who persistently lifted the eyebrow in primary gaze. A 58-year-old man (d, e) and a 36-year-old man (f, g) with visible SPC who did not persistently lift the eyebrow in primary gaze.

(Enlarge Image)

Figure 3.

Differences in the eyebrow height in primary gaze and the coronal view of the supraorbital margin between subjects without and with visible SPC. (a) A representative 23-year-old subject without visible SPC who persistently lifted the eyebrows in primary gaze. (b) A representative 25-year-old subject with visible SPC who did not. (c) The eyebrow height in the subjects without visible SPC was significantly larger than that in the subjects with visible SPC. (d, e) The coronal views of 3D-CT imaging. To evaluate the relative height of the supraorbital margin, the vertical distance (VD) between the line of the horizontal distance (HD) and the highest point of the supraorbital margin was divided by the HD between the facial midline and the middle point of the frontozygomatic suture. (f) The relative height (VD/HD) in the subjects without visible SPC was significantly larger than that in the subjects with visible SPC.

We have reported that the presence of a developed lower-positioned transverse ligament (LTL) between the superior-medial orbital rim and the lateral orbital rim on the lateral horn in the lower orbital fat space, around which the superficial levator aponeurosis turns upward to become the orbital septum, produces distinct features that include narrow eye, full eyelid, and no visible SPC, all of which correspond to characteristics of the Yayoi migrants (Fig 1a).^[7–9] To maintain an adequate visual field in primary gaze under these circumstances, increased contraction of the levator nonskeletal fast-twitch muscle fibers stretches the mechanoreceptors in Müller's muscle to enhance the levator skeletal slow-twitch muscle fibers and induce not only phasic, but also tonic, reflex contraction of the frontalis skeletal slow-twitch muscle fibers (Fig 1a).^[8–21]

We have also reported that according to digital immobilization of eyebrow movement during eyelid opening and macro- and microscopic observation of the presence of visible SPC and the development of LTL, modern Japanese people are roughly divided into people without visible SPC who have a developed LTL and persistently lift the eyebrows (Figs 1a, 2b, and 3a) and people with visible SPC who have an undeveloped LTL and do not persistently lift the eyebrows (Figs 1b, 2d, 2f, and 3b).^[9] The former correspond to the Yayoi migrant ancestry, whereas the latter correspond to the Jomon native ancestry. Because a developed LTL antagonizes opening and folding of the anterior lamella of the upper eyelid in the Japanese without visible SPC, these individuals open their eyelids by lifting the eyebrow with the anterior lamella and the LTL owing to increased tonic contraction of the frontalis muscle, in addition to the retractile force of the levator aponeurotic expansions (Figs 1a, 2b, and 3a). In the Japanese with visible SPC, the undeveloped LTL does not antagonize opening and folding of the anterior lamella, and so they open their eyelids by folding the anterior lamella on the SPC via the retractile force of the levator aponeurotic expansions without the aid of lifting the eyebrow (Figs 1b, 2d, 2f, and 3b).

We hypothesized that since Japanese who have a developed LTL and no visible SPC always lift the eyebrows in primary gaze, their supraorbital margin may be high-positioned and round as a result of the lifting force by tonic contraction of the frontalis muscle, which mechanically presses on the supraorbital margin (Fig 1a). In contrast, because wide-eyed Japanese who have an undeveloped LTL and visible natural SPC do not lift the eyebrows on primary gaze, their supraorbital margin is presumed to be low-positioned and straight (Fig 1b).

To verify this hypothesis, we evaluated whether Japanese subjects who have no visible SPC and persistently lift the eyebrow in primary gaze had a high-positioned round supraorbital margin in comparison with those who do not.