| Extraocular muscles | |
| Latin: | musculi externi bulbi oculi |
| Width: | 200b |
| Origin: | Common tendinous ring, maxillary and sphenoid bone |
| Insertion: | Tarsal plate of upper eyelid, eye |
| Blood: | Ophthalmic artery, lacrimal artery, infraorbital artery, anterior ciliary arteries, superior and inferior orbital veins |
| Nerve: | Oculomotor, trochlear and abducens nerve |
| Action: | See table |
| System: | Visual system |
The extraocular muscles, or extrinsic ocular muscles, are the seven extrinsic muscles of the eye in humans and other animals.[1] Six of the extraocular muscles, the four recti muscles, and the superior and inferior oblique muscles, control movement of the eye. The other muscle, the levator palpebrae superioris, controls eyelid elevation. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction.[2]
Since only a small part of the eye called the fovea provides sharp vision, the eye must move to follow a target. Eye movements must be precise and fast. This is seen in scenarios like reading, where the reader must shift gaze constantly. Although under voluntary control, most eye movement is accomplished without conscious effort. Precisely how the integration between voluntary and involuntary control of the eye occurs is a subject of continuing research.[3] It is known, however, that the vestibulo-ocular reflex plays an important role in the involuntary movement of the eye.
The levator palpebrae superioris is responsible for raising the upper eyelid, and this can be a voluntary or involuntary action. The other six extraocular muscles are involved in movements of the eye; these are the four recti (straight) muscles, and two oblique muscles.
The four recti muscles are named according to their relative positions of attachment – the superior rectus muscle, lateral rectus muscle, medial rectus muscle, and inferior rectus muscle. The recti muscles are all of almost equal length of around 40 mm but the lengths of their associated tendons differ.[4]
The two oblique muscles are the inferior oblique muscle and the superior oblique muscle.
| thumb | 250px | Extraocular muscles are shown in this image of the left eye (lateral view). Click on the structures for more information.default Picture: left eye from the side; Click to view informationpoly 1191 533 1187 447 1254 444 1279 490 1263 529 1191 533 Lateral rectuspoly 421 124 459 129 484 145 524 134 500 97 421 124 Trochlea of superior obliquepoly 470 198 456 180 450 153 452 137 459 130 483 145 483 155 501 170 530 183 519 184 470 198 Superior obliquepoly 524 134 557 136 657 156 770 191 856 222 927 248 981 273 1045 309 1101 341 1216 409 1208 374 1006 261 891 207 780 161 670 130 567 111 507 108 524 134 Superior obliquepoly 669 252 690 249 672 243 680 238 664 224 684 225 736 255 810 275 792 240 758 228 689 217 599 216 548 224 501 239 466 259 519 311 554 281 577 269 627 259 676 258 669 252 Superior rectuspoly 828 281 812 245 912 281 905 286 920 293 904 294 910 299 934 302 943 312 945 320 868 294 828 281 Superior rectuspoly 961 327 1054 369 1154 409 1228 438 1221 428 1091 366 992 315 952 298 961 327 Superior rectuspoly 1196 424 1238 441 1208 440 1172 434 1049 393 1015 368 968 346 859 311 813 294 740 265 705 256 676 258 669 252 689 249 672 243 679 238 665 224 685 226 737 255 810 275 792 240 770 219 732 213 727 197 770 211 798 232 804 219 812 246 828 281 834 293 860 304 908 318 954 333 945 320 943 312 933 302 910 299 904 294 920 292 905 287 912 281 929 287 920 276 898 271 902 261 896 250 909 254 939 276 937 263 953 270 951 297 953 298 962 327 965 335 1016 359 1054 382 1146 417 1196 424 1196 424 Oculomotor nervepoly 1608 418 1615 416 1619 421 1618 426 1580 443 1523 462 1466 474 1382 497 1382 487 1434 472 1394 467 1409 457 1452 461 1483 461 1567 437 1608 418 Oculomotor nervepoly 1564 449 1523 462 1466 474 1382 497 1379 512 1485 496 1539 484 1566 455 1564 449 Optic nervepoly 1383 475 1382 487 1434 472 1395 466 1383 475 Optic nervepoly 1559 439 1554 429 1521 425 1483 436 1462 438 1416 451 1409 457 1452 461 1483 461 1559 439 Optic nervepoly 1262 529 1216 559 1236 589 1332 562 1453 552 1402 538 1379 512 1382 497 1382 497 1382 487 1383 475 1394 467 1409 457 1416 452 1463 438 1422 433 1387 419 1370 385 1367 356 1350 362 1280 351 1269 364 1238 377 1208 374 1216 409 1221 428 1228 437 1238 441 1254 444 1279 490 1262 529 Common tendinous ringpoly 460 728 518 748 570 745 604 717 659 643 695 564 756 557 803 589 723 706 675 752 609 781 543 785 494 765 460 728 Inferior obliquepoly 570 744 604 717 540 696 522 679 535 725 532 747 570 744 Inferior rectuspoly 659 759 814 735 962 682 1136 623 1236 589 1217 559 1178 580 1011 635 983 659 966 653 922 687 887 688 912 675 955 651 849 678 803 709 776 735 767 733 781 715 761 715 761 710 802 698 828 682 747 699 717 711 675 752 659 759 Inferior rectuspoly 1187 453 1028 454 954 461 864 451 849 444 856 502 888 516 942 525 1016 523 1051 518 1018 496 978 507 969 518 965 516 973 498 985 494 924 487 898 489 896 481 931 476 907 469 912 465 955 474 1025 487 1054 503 1046 485 1024 479 1030 466 1049 475 1062 495 1068 514 1083 509 1189 475 1187 453 Medial rectuspoly 1193 533 1124 557 1068 514 1187 475 1193 533 Optic nervepoly 1111 563 1051 518 1011 523 1004 555 985 579 995 582 1027 588 1111 563 Optic nervepoly 944 525 951 561 924 579 897 569 853 541 856 502 890 517 944 525 Optic nervepoly 964 574 988 558 988 524 955 525 962 553 964 574 Optic nervepoly 1052 581 1111 563 1123 568 1052 581 Medial rectuspoly 1126 556 1138 562 1233 530 1191 533 1126 556 Medial rectuspoly 945 632 971 626 1004 616 1004 616 993 607 997 593 1034 596 1049 593 1043 584 1027 588 995 582 986 579 1004 556 1011 523 988 524 988 558 964 574 961 553 954 525 944 525 950 561 924 579 896 568 853 541 839 520 835 524 856 552 915 587 922 594 918 596 866 576 852 573 824 572 825 578 852 579 878 587 857 586 882 596 901 598 906 602 853 606 826 612 805 621 808 626 841 615 868 612 920 610 939 612 945 632 Ciliary ganglionpoly 912 465 908 469 931 476 896 481 898 489 924 487 985 494 973 499 965 516 969 517 978 507 1018 496 1051 518 1111 563 1123 568 1142 576 1058 606 1027 616 1005 616 1004 616 1004 616 971 626 945 632 945 634 926 644 802 675 739 694 725 702 721 708 746 699 772 689 841 674 827 683 802 698 761 710 761 715 781 715 767 733 776 735 802 710 849 678 859 672 939 649 998 631 954 651 888 687 922 687 966 653 983 659 1012 635 1033 624 1159 581 1216 559 1244 541 1240 537 1156 569 1139 562 1126 556 1124 556 1068 514 1062 495 1048 475 1030 466 1024 478 1046 485 1054 503 1025 488 912 465 Oculomotor nervepoly 460 728 518 748 531 747 535 727 522 679 541 696 604 717 659 643 696 564 756 558 803 590 727 700 741 694 774 683 819 623 808 626 805 621 827 612 841 579 825 578 824 572 846 572 851 546 835 524 839 521 853 541 856 502 849 444 841 406 815 350 778 303 729 263 701 257 676 258 719 288 761 343 691 363 626 355 634 439 630 569 565 574 529 593 511 494 540 414 634 439 626 354 587 307 554 281 519 311 466 259 420 290 386 330 355 376 370 389 374 487 373 547 365 593 355 602 395 668 460 728 Globe (human eye)poly 355 602 365 593 373 547 374 492 370 389 355 376 341 452 351 459 350 498 348 521 340 525 355 602 Irispoly 341 452 351 459 350 498 348 521 340 525 338 486 341 452 Pupilpoly 355 376 341 452 339 482 340 525 355 602 323 540 316 510 315 466 321 438 355 376 355 376 Anterior chamberpoly 630 396 634 439 630 569 565 574 529 593 511 494 540 414 634 439 630 396 Lateral rectuspoly 812 246 871 266 929 287 920 276 898 271 903 261 896 250 910 254 939 276 937 263 953 270 951 298 991 314 1093 367 1221 428 1216 409 1101 341 984 275 936 257 809 209 761 193 709 181 605 174 519 184 433 209 336 251 363 304 376 286 420 254 494 221 549 211 624 205 697 211 758 226 792 240 770 219 732 213 728 197 769 211 798 232 804 219 812 246 812 246 Levator palpebrae superioris musclepoly 676 258 628 260 577 269 554 281 588 307 627 355 692 363 762 343 720 288 676 258 Superior obliquepoly 599 216 586 208 551 211 494 221 488 224 501 239 548 224 599 216 599 216 Superior obliquepoly 851 546 846 572 852 573 866 576 918 596 922 594 915 587 856 552 851 546 Optic nervepoly 839 579 841 579 827 612 853 606 906 602 901 598 882 596 857 586 878 587 852 579 839 579 Medial rectuspoly 962 327 965 335 1016 359 1054 382 1146 417 1190 423 1154 409 1054 369 962 327 Orbitpoly 945 320 868 294 828 281 834 293 860 304 908 318 954 333 945 320 Orbitpoly 1238 441 1208 440 1172 434 1049 393 1015 368 968 346 859 311 813 294 740 265 729 263 778 303 815 350 841 406 849 444 864 451 954 461 1028 454 1187 453 1189 475 1187 447 1254 444 1238 441 Orbitdesc bottom-right |
The movements of the extraocular muscles take place under the influence of a system of extraocular muscle pulleys, soft tissue pulleys in the orbit. The extraocular muscle pulley system is fundamental to the movement of the eye muscles, in particular also to ensure conformity to Listing's law. Certain diseases of the pulleys (heterotopy, instability, and hindrance of the pulleys) cause particular patterns of incomitant strabismus. Defective pulley functions can be improved by surgical interventions.[5] [6]
Four of the extraocular muscles have their origin in the back of the orbit in a fibrous ring called the common tendinous ring: the four recti muscles. The four recti muscles attach directly to the front half of the eye (anterior to the eye's equator), and are named after their straight paths.[3]
Medial and lateral are relative terms. Medial indicates near the midline, and lateral describes a position away from the midline. Thus, the medial rectus is the muscle closest to the nose. The superior and inferior recti do not pull straight back on the eye, because both muscles also pull slightly medially. This posterior medial angle causes the eye to roll with contraction of either the superior rectus muscle or the inferior rectus muscle. The extent of rolling in the recti is less than the oblique, and opposite from it.[3]
The superior oblique muscle originates at the back of the orbit (a little closer to the medial rectus, though medial to it), getting rounder as it[3] courses forward to a rigid, cartilaginous pulley, called the trochlea, on the upper, nasal wall of the orbit. The muscle becomes tendinous about 10mm before it passes through the pulley, turning sharply across the orbit, and inserts on the lateral, posterior part of the globe. Thus, the superior oblique travels posteriorly for the last part of its path, going over the top of the eye. Due to its unique path, the superior oblique, when activated, pulls the eye downward and laterally.[7]
The last muscle is the inferior oblique, which originates at the lower front of the nasal orbital wall, passes inferiorly over the inferior rectus muscle on its path laterally and posteriorly, and inserts under the lateral rectus muscle on the lateral, posterior part of the globe. Thus, the inferior oblique pulls the eye upward and laterally.[7] [8] [9]
The extraocular muscles are supplied mainly by branches of the ophthalmic artery. This is done either directly or indirectly, as in the lateral rectus muscle, via the lacrimal artery, a main branch of the ophthalmic artery. Additional branches of the ophthalmic artery include the ciliary arteries, which branch into the anterior ciliary arteries. Each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one. The exact number and arrangement of these ciliary arteries may vary. Branches of the infraorbital artery supply the inferior rectus and inferior oblique muscles.
| Cranial nerve | Muscle | |
|---|---|---|
| Oculomotor nerve ( N. III) | Superior rectus muscleInferior rectus muscle Medial rectus muscle Inferior oblique muscle | |
| Levator palpebrae superioris muscle | ||
| Trochlear nerve ( N. IV) | Superior oblique muscle | |
| Abducens nerve ( N. VI) | Lateral rectus muscle |
The extraocular muscles develop along with Tenon's capsule (part of the ligaments) and the fatty tissue of the eye socket (orbit). There are three centers of growth that are important in the development of the eye, and each is associated with a nerve. Hence the subsequent nerve supply (innervation) of the eye muscles is from three cranial nerves. The development of the extraocular muscles is dependent on the normal development of the eye socket, while the formation of the ligament is fully independent.
See main article: Eye movement.
The oculomotor nerve (III), trochlear nerve (IV) and abducens nerve (VI) coordinate eye movement. The oculomotor nerve controls all muscles of the eye except for the superior oblique muscle controlled by the trochlear nerve (IV), and the lateral rectus muscle controlled by the abducens nerve (VI). This means the ability of the eye to look down and inwards is controlled by the trochlear nerve (IV), the ability to look outwards is controlled by the abducens nerve (VI), and all other movements are controlled by the oculomotor nerve (III).[10]
Intermediate directions are controlled by simultaneous actions of multiple muscles. When one shifts the gaze horizontally, one eye will move laterally (toward the side) and the other will move medially (toward the midline). This may be neurally coordinated by the central nervous system, to make the eyes move together and almost involuntarily. This is a key factor in the study of strabismus, namely, the inability of the eyes to be directed to one point.
There are two main kinds of movement: conjugate movement (the eyes move in the same direction) and disjunctive (opposite directions). The former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is usually triggered by the nearness of the target object. A "see-saw" movement, namely, one eye looking up and the other down, is possible, but not voluntarily; this effect is brought on by putting a prism in front of one eye, so the relevant image is apparently displaced. To avoid double vision from non-corresponding points, the eye with the prism must move up or down, following the image passing through the prism. Likewise conjugate torsion (rolling) on the anteroposterior axis (from the front to the back) can occur naturally, such as when one tips one's head to one shoulder; the torsion, in the opposite direction, keeps the image vertical.
The muscles show little inertia - a shutdown of one muscle is not due to checking of the antagonist, so the motion is not ballistic.[3]
The vestibulo-ocular reflex is a reflex that stabilizes gaze when the head is moved. The reflex involves compensatory eye movements driven by inhibitory and excitatory signals.
Below is a table of each extraocular muscle and their innervation, origins and insertions, and the primary actions of the muscles (the secondary and tertiary actions are also included, where applicable).[11]
| Muscle | Innervation | Origin | Insertion | Primary action | Secondary action | Tertiary action | |
|---|---|---|---|---|---|---|---|
| Medial rectus | Oculomotor nerve (inferior branch) | Common tendinous ring | Eye (anterior, medial surface) | Adduction | |||
| Lateral rectus | Abducens nerve | Common tendinous ring | Eye (anterior, lateral surface) | Abduction | |||
| Superior rectus | Oculomotor nerve (superior branch) | Common tendinous ring | Eye (anterior, superior surface) | Elevation | Incyclotorsion | Adduction | |
| Inferior rectus | Oculomotor nerve (inferior branch) | Common tendinous ring | Eye (anterior, inferior surface) | Depression | Excyclotorsion | Adduction | |
| Superior oblique | Trochlear nerve | Sphenoid bone via the Trochlea | Eye (posterior, superior, lateral surface) | Incyclotorsion | Depression | Abduction | |
| Inferior oblique | Oculomotor nerve (inferior branch) | Maxillary bone | Eye (posterior, inferior, lateral surface) | Excyclotorsion | Elevation | Abduction | |
| Levator palpebrae superioris | Oculomotor nerve | Sphenoid bone | Tarsal plate of upper eyelid | Elevation/retractionof the upper eyelid |
Damage to the cranial nerves may affect the movement of the eye. Damage may result in double vision (diplopia) because the movements of the eyes are not synchronized. Abnormalities of visual movement may also be seen on examination, such as jittering (nystagmus).[12]
Damage to the oculomotor nerve (III) can cause double vision and inability to coordinate the movements of both eyes (strabismus), also eyelid drooping (ptosis) and pupil dilation (mydriasis).[13] Lesions may also lead to inability to open the eye due to paralysis of the levator palpebrae muscle. Individuals suffering from a lesion to the oculomotor nerve may compensate by tilting their heads to alleviate symptoms due to paralysis of one or more of the eye muscles it controls.
Damage to the trochlear nerve (IV) can also cause double vision with the eye adducted and elevated. The result will be an eye which can not move downwards properly (especially downwards when in an inward position). This is due to impairment in the superior oblique muscle.
Damage to the abducens nerve (VI) can also result in double vision.[13] This is due to impairment in the lateral rectus muscle, supplied by the abducens nerve.
Amblyopia also known as lazy eye is a condition of diminshed sight in one eye.
Ophthalmoparesis is weakness or paralysis of one or more extraocular muscles.
See also: Eye examination and Cranial nerve examination. The initial clinical examination of the extraoccular eye muscles is done by examining the movement of the globe of the eye through the six cardinal eye movements. When the eye is turned out (temporally) and horizontally, the function of the lateral rectus muscle is tested. When the eye is turned in (nasally) and horizontally, the function of the medial rectus muscle is being tested. When turning the eye down and in, the inferior rectus is contracting. When turning it up and in the superior rectus is contracting. Paradoxically, turning the eye up and out uses the inferior oblique muscle, and turning it down and out uses the superior oblique. All of these six movements can be tested by drawing a large "H" in the air with a finger or other object in front of a patient's face and having them follow the tip of the finger or object with their eyes without moving their head. Having them focus on the object as it is moved in toward their face in the midline will test convergence, or the eyes' ability to turn inward simultaneously to focus on a near object.
To evaluate for weakness or imbalance of the muscles, a penlight is shone directly on the corneas. Expected normal results of the corneal light reflex is when the penlight's reflection is located in the centre of both corneas, equally.[14]