| Inferior rectus | |
|---|---|
 Theinferior rectus muscle, is shown in this superior view of the eye, along with its axis of rotation. The other muscle is the superior oblique muscle, which angles around the trochlea. | |
| Details | |
| Origin | Common tendinous ring at the orbital apex |
| Insertion | 6.8 mm inferior to thecorneal limbus |
| Artery | Inferior muscular branch of theophthalmic artery,infraorbital artery |
| Vein | Inferior muscular branch of theophthalmic vein |
| Nerve | Inferior branch of oculomotor nerve |
| Actions | Depression,adduction,extorsion |
| Identifiers | |
| Latin | musculus rectus inferior bulbi |
| TA98 | A15.2.07.011 |
| TA2 | 2043 |
| FMA | 49036 |
| Anatomical terms of muscle | |
Theinferior rectus muscle is amuscle in theorbit near theeye. It is one of the fourrecti muscles in the group ofextraocular muscles. It originates from thecommon tendinous ring, and inserts into the anteroinferior surface of the eye. It depresses the eye (downwards).
The inferior rectus muscle originates from thecommon tendinous ring (annulus of Zinn).[1] It inserts into the anteroinferior surface of the eye.[2] This insertion has a width of around 10.5 mm.[2] It is around 6.6 mm from thecorneal limbus.[2]
The inferior rectus muscle is supplied by an inferior muscular branch of theophthalmic artery.[1] It may also be supplied by a branch of theinfraorbital artery.[1] It is drained by the corresponding veins: the inferior muscular branch of theophthalmic vein, and sometimes a branch of theinfraorbital vein.[1]
The inferior rectus muscle is supplied by the inferior division of theoculomotor nerve (III).[1]
The inferior rectus muscle develops from the embryonicmesoderm in theorbit of theskull.[1][3] This is similar to the otherextraocular muscles.[3]
The insertion of the inferior rectus muscle is around 6 mm from the insertion of themedial rectus muscle, and around 8 mm from the insertion of thelateral rectus muscle.[2] Aparasympathetic branch that supplies theciliary muscles of thepupil passes close to the inferior rectus muscle.[1]
Very rarely, the inferior rectus muscle may be congenitally absent.[3][4] This may cause inferior rectus palsy, where the eye cannot be depressed.[3]
The inferior rectus muscledepresses,adducts, and helpsextort the eye.[1] It is the only muscle that is capable of depressing thepupil when it is in a fully abducted position.[5]
If the inferior rectus muscle isdamaged,weak, orparalysed, this can causestrabismus.[1][6] This can lead to elevation of theeye, as thesuperior rectus muscle remains stronger.[6] For minor cases, prism glasses can be used to gradually realign the eye.[6] Alternatively for serious cases, it may be surgically corrected by slightly weakening thesuperior rectus muscle (opposite) - this reduces the elevation of the eye, and corrects the strabismus.[6] This procedure may lead to overcorrection of the strabismus, but is otherwise generally successful.[7]
Anysurgery on the inferior rectus muscle may damage theparasympathetic branches to theciliary muscles of thepupil.[1] This may cause problems with control of the pupil.[1] Nearby blood vessels and nerves may also be damaged.[1]
