AN31.1-5 | Orbit — Glossary

Common tendinous ring at the orbital apex from which the four rectus muscles originate; transmits the optic nerve, ophthalmic artery, and CN III, VI.

Extraocular muscle supplied by CN III (superior division) that primarily elevates the eye; also adducts and medially rotates it.

Extraocular muscle supplied by the abducens nerve (CN VI) that abducts (laterally deviates) the eyeball.

Extraocular muscle supplied by the trochlear nerve (CN IV); passes through the trochlea and primarily intorts, depresses, and abducts the eye.

Extraocular muscle arising from the orbital floor, supplied by CN III; primarily extorts and elevates the eye.

A fibrocartilaginous pulley on the superomedial orbital margin through which the tendon of the superior oblique muscle passes before inserting on the sclera.

Cranial nerve supplying the superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris; also carries parasympathetic fibres to the sphincter pupillae and ciliary muscle.

The only cranial nerve that exits from the dorsal brainstem; supplies the superior oblique muscle. Has the longest intracranial course, making it vulnerable to head trauma.

Cranial nerve with a long intracranial course that supplies the lateral rectus muscle; vulnerable to raised intracranial pressure causing a false localising sign.

First division of the trigeminal nerve providing sensory innervation to the orbit, upper eyelid, forehead, and nose via its frontal, lacrimal, and nasociliary branches.

Branch of the internal carotid artery that enters the orbit through the optic canal; supplies the eye, orbital contents, and adjacent facial structures including the central retinal artery.

Sympathetic cell bodies at spinal cord levels C8–T2 (of Budge) that give rise to the second-order neuron of the ocular sympathetic pathway.

Clinical triad of miosis (constricted pupil), ptosis (drooping eyelid), and anhidrosis (loss of facial sweating) caused by disruption of the sympathetic pathway to the eye at any of its three neuron levels.

The uppermost sympathetic ganglion in the neck where the second-order sympathetic neuron synapses; the third-order neuron then ascends along the internal carotid artery to reach the eye.

Smooth muscle of the iris with radial fibres supplied by sympathetic nerves; contraction causes mydriasis (pupil dilation). Paralysis in Horner's syndrome causes miosis.

Serous gland in the superolateral orbit divided into orbital and palpebral parts by the levator aponeurosis; produces the aqueous component of the tear film.

Bony canal draining tears from the lacrimal sac into the inferior meatus of the nasal cavity; blockage causes epiphora (watery eye) and may lead to dacryocystitis.

Parasympathetic ganglion in the pterygopalatine fossa that relays secretomotor fibres (from CN VII via the greater petrosal nerve) to the lacrimal gland, nasal, and palatal glands.

Misalignment of the eyes (squint) where the visual axes do not converge on the fixation point; may be paralytic (nerve palsy) or non-paralytic (congenital).

Double vision resulting from misalignment of the visual axes; binocular diplopia disappears when one eye is covered and is a key symptom of extraocular muscle or nerve palsy.

Drooping of the upper eyelid; in CN III palsy it is complete (levator palpebrae paralysis), while in Horner's syndrome it is partial (Mueller's muscle denervation).

Dilation of the pupil; in CN III palsy, parasympathetic disruption causes a fixed dilated pupil unresponsive to light ("blown pupil").