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HFA 213 Week 12 The Orbit STRUCTURE OF THE EYEBALL Connective tissue layer = Sclera + Cornea Vascular layer = Choroid + Iris Neural layer = Retina INTRA-OCULAR SMOOTH MUSCLE Ciliary muscle 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 Vitreous humor Aqueous humor (Anterior and Posterior chambers) Nerve supply: Sympathetic fibres from superior cervical ganglion Light reflex 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 well as elevate and depress the eye. Medial and lateral rectus are pure adductors and abductors Elevation is performed by superior rectus and inferior oblique The oblique muscles The oblique muscles attach behind the equator They pull anteriorly and medially Therefore they abduct the eye Depression is performed by inferior rectus and superior oblique Intorsion and extortion cancel each other out HFA 213 Week 12 The Orbit ELEVATION AND DEPRESSION Acting alone, superior oblique will turn the eye “down and out”. BUT People with a trochlear nerve lesion can’t look at the end of their nose. BECAUSE Superior oblique never acts alone. It works with inferior rectus to depress the eye. NERVES OF THE ORBIT The Optic nerve (II) enters through the optic canal Other nerves enter through superior orbital fissure: Three enter outside the tendinous ring: Lacrimal nerve (V1) Frontal nerve (V1) Trochlear nerve (IV) These are all found superficially just under the orbital roof If the eye is abducted Inferior rectus is an effective depressor Superior oblique can only cause intorsion Three enter inside the tendinous ring: Oculomotor nerve (III) Nasociliary nerve (V1) Abducens nerve (VI) These are located deeper inside the cone of muscles If the eye is adducted Inferior rectus can only cause extorsion Superior oblique is the effective depressor The branches of the Ophthalmic (V1) are all sensory: 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 oblique which couple to produce effective elevation of the eye The Nasociliary supplies the surface of the cornea (long ciliary nerves) and has branches to the ethmoid air cells, 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) Sphincter pupillae and ciliary muscle Sympathetic (via internal carotid plexuses) Trochlea nerve (IV) - Supplies superior oblique muscle Patient has trouble depressing the adducted eye can’t look at tip of nose, or at feet going down stairs Dilator pupillae 2. Extraocular smooth muscle (Sympathetic) Superior tarsal muscle (in levator palpebrae superioris) “Muller’s” muscle (Not well understood – or seen) holds the eye in the In order to avoid diplopia, the patient tends to tilt head because the affected eye also becomes extorted (rotated by the unopposed action of inferior oblique) front of the orbit 3. Lacrimal gland Parasympathetic fibres from pterygopalatine ganglion initially carried with the zygomatic nerve transfer to the lacrimal nerve Abducens nerve (VI) – Supplies lateral rectus muscle Patient has trouble abducting the affected eye. In order to avoid diplopia, the patient tends to look sideways 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 Horner’s Syndrome: Damage to the cervical sympathetic trunk: 1. Ptosis - drooping of the upper eyelid (loss of superior tarsal muscle) 2. Miosis - pupillary constriction (loss of dilator pupillae) 3. Enophthalmia – sunken eye (loss of Muller’s muscle) 4. Anhydrosis – loss of facial sweating and vasodilatation Patient has trouble with: Elevating the eye or upper eyelid Close-up vision: Lens accommodation Constricting the pupil Adducting the eye