Table 1. Mensuration of Human Extraocular Muscles*
|
INSERTIONS |
|
|
Distance of Insertion Midpoint from
Cornea |
|
|
Adults |
Infants |
|
|
Fuchs50 |
Weiss56 |
Apt64 |
Whitnall44 |
Weiss56 |
|
Muscle |
Average |
Range |
Average |
Range |
Average |
Range |
Average of 12 authors |
Average |
Range |
Range of Insertion Distance from Cornea Across
Entire Tendon, Greatest-shortest Motais52 |
Medial rectus |
5.5 |
4.3–6.7 |
5.85 |
5.0–6.7 |
5.3 |
3.6–7.0 |
5.84 |
3.6 |
3.0–4.3 |
5.5–7.0 |
Inferior rectus |
6.5 |
5.3–8.2 |
6.85 |
6.0–7.5 |
6.8 |
4.8–8.5 |
6.65 |
5.0 |
4.0–5.5 |
5.5–8.0 |
Lateral rectus |
6.9 |
5.3–8.2 |
6.75 |
6.25–7.75 |
6.9 |
5.4–8.5 |
7.18 |
4.9 |
4.0–5.5 |
6.7–7.0 |
Superior rectus |
7.7 |
6.8–9.0 |
8.01 |
6.75–9.0 |
7.9 |
6.2–9.2 |
7.88 |
5.8 |
5.0–7.0 |
6.5–11.0 |
|
TENDON AT INSERTION† |
|
|
|
Width |
|
|
|
Adults |
Infants |
|
|
Length |
Fuchs50
(emmetropic eyes) |
Weiss56 |
Adachi46 |
Weiss56 |
|
Muscle |
Merkel43 |
Hesser48 |
Average |
Range |
Average |
Range |
Average |
Average |
Shape |
Medial rectus |
3.7 |
3.5 |
10.3 |
8.8–12.0 |
10.76 |
10.0–12.5 |
9.9 |
7.35 |
Straight or slightly convex forward |
Inferior rectus |
5.5 |
4.5 |
9.8 |
7.8–13.2 |
10.35 |
10.0–11.1 |
9.0 |
6.35 |
Convex forward, lateral part more anterior,
frequently greater width lateral to vertical meridian |
Lateral rectus |
8.8 |
8.0 |
9.2 |
8.5–10.2 |
9.67 |
8.3–12.0 |
8.4 |
5.85 |
Straight |
Superior rectus |
5.8 |
5.0 |
10.6 |
8.5–13.2 |
10.75 |
10.0–11.25 |
10.0 |
6.95 |
Convex forward, lateral part more anterior,
⅔ of width lateral to vertical meridian |
MUSCLES |
Cross Section (mm2) |
|
Length Excluding Tendon |
Measured Maximum |
|
|
|
|
|
|
|
|
|
Adults |
Infants |
Nakagawa53§ |
|
|
Ratio of Area to Lateral Rectus Area
Volkmann55 |
|
Thickness Schneller66 |
Width Schneller66 |
Muscle |
Whitnall44 |
Volkmann55 |
Adachi46 |
Mühlendyck65 |
Schneller66 |
Male |
Female |
Calculated: Volkmann55‖
|
Infants Schneller66 |
Weight (g) |
Adult |
Infant |
Adult |
Infant |
Medial rectus |
|
40.8 |
40.7 |
22.6 |
28.0 |
31.0 |
28.1 |
17.39 |
10.27 |
1.04 |
0.75 |
1.69 |
1.3 |
10.3 |
7.9 |
Inferior rectus |
|
40.0 |
|
17.8 |
|
31.1 |
28.3 |
15.85 |
|
0.95 |
0.67 |
|
|
|
|
Lateral rectus |
|
40.6 |
45.8 |
24.8 |
31.6 |
47.6 |
40.8 |
16.73 |
8.63 |
1.0 |
0.72 |
1.6 |
1.25 |
9.2 |
6.9 |
Superior rectus |
|
41.8 |
|
23.5 |
|
24.0 |
20.9 |
11.34 |
|
0.68 |
0.51 |
|
|
|
|
Superior oblique |
40 |
32.2 |
|
|
|
10.0 |
11.4 |
8.36 |
|
0.50 |
0.29 |
|
|
|
|
Inferior oblique |
37 |
34.5 |
|
|
|
17.3 |
14.1 |
7.89 |
|
0.47 |
0.29 |
|
|
|
|
|
Angle to Vertical Plane (%)
Duke-Elder39 |
Arc of contact (mm) |
Innervation: |
Action‖ |
|
Muscle |
Average |
Range |
Zoth57 |
Cranial Nerve |
Primary |
Secondary |
Medial rectus |
|
|
6.33 |
III |
Adduction (99.9%) |
None |
Inferior rectus |
23 |
|
9.83 |
III |
Infraduction (74%) |
Excycloduction (16%) |
|
|
|
|
|
|
Adduction (10%) |
Lateral rectus |
|
|
13.25 |
VI |
Abduction (99.9%) |
None |
Superior rectus |
23 |
|
8.92 |
III |
Supraduction (76%) |
Incycloduction (16%) |
|
|
|
|
|
|
Abduction (8%) |
Superior oblique |
54 |
32–64 |
5.23 |
IV |
Incycloduction (64%) |
Infraduction (33%) |
|
|
|
|
|
|
Abduction (3%) |
|
51 |
33–57 |
16.74 |
III |
Excycloduction (59%) |
Supraduction (40%) |
Inferior oblique |
|
|
|
|
|
Abduction (1%) |
|
Number of Muscle Fibers¶ |
|
|
|
Children |
|
|
Adults |
Infants |
18 Months |
Size of Motor Unit** |
Muscle |
Bors230 |
Kato51 |
Tergast229 |
Torre232 |
Goldschmidt47 |
Kato51 |
Goldschmidt47 |
Mühlendyck65 |
Tergast229 |
Torre232 |
Bors230 |
Goldschmidt47 |
Medial rectus |
21,950 |
28,631 |
5,580 |
|
41,575 |
45,529 |
41,515 |
25,932 |
1:1.7 |
|
1:4.8 |
1:3.9 |
Inferior rectus |
20,809 |
25,880 |
10,350 |
|
|
23,79 |
|
|
1:2.0 |
|
1:6.3 |
|
Lateral rectus |
27,214 |
35,058 |
11,965 |
24,400 |
31,639 |
22,608 |
28,075 |
23,327 |
1:3.3 |
1:4.9, 1:6 |
1:5.8 |
1:6.6 |
|
|
|
19,760 |
31,735 |
|
|
|
|
|
|
|
|
Superior rectus |
20,156 |
|
|
|
28,084 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1:4.3 |
|
Superior oblique |
9,254 |
14,866 |
|
|
|
16,135 |
|
|
|
1:5.3,1:6.8 |
1:5.2 |
|
Inferior oblique |
17,557 |
|
|
|
|
15,488 |
|
|
|
|
1:7.0 |
|
Nerves¶ |
Number of Nerve Fibers |
|
|
|
Bors230 |
Bjorkman & Wolfahrt231 |
Torre232 |
Nerve |
Rosenthal228 |
Tergast229 |
Proximal |
Distal |
Proximal |
Proximal |
Distal |
III |
15,000 |
|
13,763 |
|
24,000 |
|
|
IV |
1100–1200 |
|
1782 |
|
3400 |
2440 |
|
|
|
|
|
|
|
2100 |
|
VI |
2000–2500 |
3600 |
3862 |
4698 |
6600 |
5000 |
4650 |
|
|
|
|
|
|
3300 |
|
*Dimensions in millimeters; dimensions refer to adults
unless otherwise specified.
†See Figure 6 for oblique muscles.
‡Maximum cross section occurs at the approximate level of the posterior
pole of the globe.
§Based on length, weight, and assumed density.
‖Percentages calculated from Robinson.344
¶Double entries refer to two specimens.
**Number of muscle fibers per nerve fiber.
|