Normative measurements of the Chinese extraocular musculature by high-field magnetic resonance imaging.
OBJECTIVE
To establish the normal measurements of diameter and cross-sectional area of the Chinese extraocular muscles (EOMs) and optic nerve-sheath complex (ON) as seen on high-field (3-Tesla; 3T) magnetic resonance imaging (MRI).


METHODS
Coronal 3T MRI of the orbit (TR, 700 ms; TE, 15 ms; FOV, 160 mm; matrix, 256 x 256; slice thickness, 1 mm; and slice gap, 0) was performed on 80 normal Chinese volunteers. T1-weighted images were analyzed with computer-assisted segmentation. The diameter and the cross-sectional area of EOMs and the ON were measured from the image plane at the posterior aspect of the globe and at 7 mm behind the globe. The maximum diameter of EOM was measured from their respective reconstructed images.


RESULTS
The normal measurement (mean +/- SD) of diameter at the posterior aspect of the globe: medial rectus (MR), 3.6 +/- 0.4 mm; inferior rectus (IR), 3.7 +/- 0.8 mm; lateral rectus (LR), 2.3 +/- 0.5 mm; superior oblique (SO), 2.4 +/- 0.6 mm; and the ON, 5.4 +/- 0.7 mm. The normal measurement of diameter 7 mm behind the globe: MR, 3.2 +/- 0.6 mm; IR, 3.9 +/- 0.8 mm; LR, 4.0 +/- 0.8 mm; SO, 2.2 +/- 0.7 mm; and ON, 4.2 +/- 0.5 mm. The normal measurement of cross-sectional area at the posterior aspect of the globe: superior muscle group (SMG), 28.2 +/- 6.5 mm(2); MR, 25.5 +/- 3.2 mm(2); IR, 26.9 +/- 7.2 mm(2); LR, 17.3 +/- 3.9 mm(2); SO, 10.5 +/- 3.5 mm(2); and ON, 27.6 +/- 6.1 mm(2). The normal measurement of cross-sectional area 7 mm behind the globe: SMG, 24.1 +/- 6.6 mm(2); MR, 19.1 +/- 4.6 mm(2); IR, 29.5 +/- 6.6 mm(2); LR, 32.3 +/- 6.5 mm(2); SO, 9.7 +/- 3.9 mm(2); and ON, 17.1 +/- 2.9 mm(2). The normal measurement of maximum diameter: SMG, 4.8 +/- 1.1 mm; MR, 5.1 +/- 0.9 mm; IR, 5.4 +/- 1.0 mm; and LR, 4.5 +/- 0.9 mm.


CONCLUSIONS
The Chinese 3T MRI EOMs and ON normative data may be useful in determining pathologic enlargement of the EOMs and ON in various orbital conditions. (ClinicalTrials.gov number, NCT00348413.).
Shen
Sunny
S
Singapore National Eye Centre, Singapore.
Fong
Kee Siew
KS
Wong
Hwee Bee
HB
Looi
Audrey
A
Chan
Ling Ling
LL
Rootman
Jack
J
Seah
Lay Leng
LL
D000328:Adult; D017677:Age Distribution; D019412:Anatomy, Cross-Sectional; D044466:Asian People; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000033:anatomy & histology*; D009900:Optic Nerve / Q000033:anatomy & histology; D012016:Reference Values; D017678:Sex Distribution