Magnetic Resonance Imaging Demonstrates Differences in Brow and Upper Eyelid Fat and Muscle Layers Between East Asians and Caucasians

To objectively quantify, in East Asians and Caucasians, the width and distribution of the retro-orbicularis oculi and frontalis fat (ROOF) pad, subcutaneous fat, and orbicularis oculi muscle (OOM) at the superior orbital rim margin as well as 5 mm superior and inferior to this point. Thirty adults were studied by high-resolution, surface coil MRI. In the quasi-sagittal image through the globe center, the ROOF, subcutaneous fat, and OOM thickness were measured anterior to the orbital septum, at 3 points: at the superior orbital rim, and 5 mm superior, and 5 mm inferior to the rim. Seventeen subjects were of East Asian descent and 13 were Caucasian. Mean age (±standard deviation) was 49 (±16, range 18-72 years) and 53 (±17, range 29-80 years), respectively. Subcutaneous fat, OOM, and ROOF individual and total anteroposterior layer thickness at the superior orbital rim was similar between East Asians and Caucasians, with average ROOF 63% to 66% (4.5 ± 1.0, 4.7 ± 1.5 mm) of the width at the rim, and 33% to 34% (1.7 ± 0.7-1.8 ± 1.0 mm) 5 mm superiorly. In Caucasians, 12 of 13 patients (92%) had no measurable ROOF 5 mm inferior to the orbital rim. Values for Caucasians were significantly smaller than for East Asians 5 mm under the rim, where the East Asian eyelid layers anterior to the orbital septum averaged: subcutaneous fat 0.9 ± 0.4 mm, OOM 1.2 ± 0.3 mm, ROOF 1.8 ± 1.2 mm, and preaponeurotic fat 1.1 ± 0.9 mm. At the same level, the Caucasian eyelid measured: subcutaneous fat 0.6 ± 0.5 mm and OOM 1.4 ± 0.3 mm. Retro-orbicularis oculi and frontalis fat is the major contributor to the anteroposterior thickness of the eyelid at the level of the superior orbital rim in both East Asians and Caucasians. In East Asians, the ROOF comprises much of the total width inferior to the superior rim, whereas the Caucasian eyelid is mostly muscular. In Caucasians, ROOF is centered around the rim and extends intra-orbitally onto the roof as opposed to East Asians in which it continues inferiorly, into the upper eyelid. These anatomic variations explain some of the differences in surface anatomy between ethnic groups.