HFA 213 Week 12 The Orbit STRUCTURE OF THE EYEBALL INTRA-OCULAR SMOOTH MUSCLE Connective tissue layer = Sclera + Cornea Ciliary muscle Vascular layer = Choroid + Iris Neural layer = Retina Accommodation (focussing) Circular and longitudinal fibres Both act to allow the lens to become more spherical (close up) Nerve supply: parasympathetic fibres in Oculomotor (CN III) nerve Pupillary muscles (sphincter and dilator) Control pupil size (aperture) Sphincter Pupillae Circular muscle in inner 1/3 of the iris Nerve supply: parasympathetic fibres in Oculomotor (CN III) nerve Dilator Pupillae Radial muscle in outer 2/3 of the iris Ciliary body, Suspensory ligament and lens Nerve supply: Sympathetic fibres from superior cervical ganglion Vitreous humor Light reflex Aqueous humor (Anterior and Posterior chambers) Increased light on retina (Optic nerve - CN II) Pupil constricts (Oculomotor nerve - CN III) Accommodation reflex CN III - focus, constrict, converge HFA 213 Week 12 The Orbit GEOMETRY OF THE ORBIT EXTRA-OCULAR STRIATED MUSCLES THE ORBITS DIVERGE but THE OPTIC AXES ARE PARALLEL The rectus muscles The origin of the rectus muscles is from a tendinous ring surrounding the optic foramen. The rectus muscles attach in front of the equator of the eye They pull posteriorly and medially. Therefore the superior and inferior rectus muscles adduct as Medial and lateral rectus are pure adductors and abductors well as elevate and depress the eye. Elevation is performed by superior rectus and inferior oblique The oblique muscles The oblique muscles attach behind the equator Depression is performed by inferior rectus and superior oblique They pull anteriorly and medially Therefore they abduct the eye Intorsion and extortion cancel each other out HFA 213 Week 12 The Orbit ELEVATION AND DEPRESSION NERVES OF THE ORBIT Acting alone, superior oblique will turn the eye “down and out”. The Optic nerve (II) enters through the optic canal BUT Other nerves enter through superior orbital fissure: People with a trochlear nerve lesion can’t look at the end of their nose. Three enter outside the tendinous ring: 1 BECAUSE Lacrimal nerve (V ) 1 Superior oblique never acts alone. Frontal nerve (V ) It works with inferior rectus to depress the eye. Trochlear nerve (IV) These are all found superficially just under the orbital roof If the eye is abducted Inferior rectus is an effective depressor Three enter inside the tendinous ring: Superior oblique can only cause intorsion Oculomotor nerve (III) 1 Nasociliary nerve (V ) Abducens nerve (VI) These are located deeper inside the cone of muscles If the eye is adducted 1 Inferior rectus can only cause extorsion The branches of the Ophthalmic (V ) are all sensory: Superior oblique is the effective depressor Frontal => Supraorbital and Supratrochlear Lacrimal supplies lateral part of upper eyelid (and receives some parasympathetic fibres from the pterygopalatine ganglion) The same applies to superior rectus and inferior The Nasociliary supplies the surface of the cornea (long oblique which couple to produce effective ciliary nerves) and has branches to the ethmoid air cells, elevation of the eye nose and nasal cavity HFA 213 Week 12 The Orbit AUTONOMIC NERVES OF THE ORBIT MOTOR NERVES OF THE ORBIT Nerve lesions: 1. Intraocular smooth muscle (short ciliary nerves) Parasympathetic (Oculomotor nerve and ciliary ganglion) Trochlea nerve (IV) - Supplies superior oblique muscle Sphincter pupillae and ciliary muscle Patient has trouble depressing the adducted eye can’t look at Sympathetic (via internal carotid plexuses) tip of nose, or at feet going down stairs Dilator pupillae 2. Extraocular smooth muscle (Sympathetic) In order to avoid diplopia, the patient tends to tilt head Superior tarsal muscle (in levator palpebrae superioris) because the affected eye also becomes extorted (rotated “Muller’s” muscle (Not well understood – or seen) holds the eye in the by the unopposed action of inferior oblique) front of the orbit 3. Lacrimal gland Abducens nerve (VI) – Supplies lateral rectus muscle Parasympathetic fibres from pterygopalatine ganglion Patient has trouble abducting the affected eye. initially carried with the zygomatic nerve transfer to the In order to avoid diplopia, the patient tends to look sideways lacrimal nerve so that the affected eye can be used in adduction. Oculomotor nerve (III) – Supplies all other extra ocular muscles as well as parasympathetic innervation to intraocular muscles Patient has trouble with: Elevating the eye or upper eyelid Close-up vision: Horner’s Syndrome: Damage to the cervical sympathetic trunk: Lens accommodation 1. Ptosis - drooping of the upper eyelid (loss of superior tarsal muscle) Constricting the pupil 2. Miosis - pupillary constriction (loss of dilator pupillae) Adducting the eye 3. Enophthalmia – sunken eye (loss of Muller’s muscle) 4. Anhydrosis – loss of facial sweating and vasodilatation .