GNK485 The eye and related structures Prof MC Bosman 2012
Surface anatomy Bony orbit Eyeball and Lacrimal apparatus Extra-ocular muscles Movements of the eye Innervation Arterial supply and venous drainage Visual- and reflex pathways Clinical applications
Surface anatomy Sclera Cornea Palpebral fissure Sclerocorneal juncture Pupil Iris Superior eyelid Inferior eyelid Eyelashes Conjunctiva bulbar and scleral Conjunctival sac Medial angle of the eye: lacrimal lake, lacrimal caruncle, semilunar conjunctival fold lacrimal punctum, lacrimal papilla
Bony orbit Orbit - Cone-shaped - Roof - Floor - Medial wall lamina papyracea - Lateral wall - Apertures optic canal orbital fissures superior inferior nasolacrimal canal
Bony orbit Orbit - Cone-shaped - Roof - Floor - Medial wall lamina papyracea - Lateral wall - Apertures optic canal orbital fissures superior inferior nasolacrimal canal
Eyeball
Eyeball
Eyeball
Eyeball - layers Outer: Fibrous [white of eye] Sclera opaque [posterior 5/6] Cornea transparent [anterior 1/6] Middle: Vascular [uvea] Choroid dark, reddish brown, blood vessels located near sclera, capillaries innermost Ciliary body folds are ciliary processes secrete aqueous humor suspensory ligaments to lens Iris pupil sphincter and dilator pupillae [autonomic control] Inner layer Retina - optic part: neural layer, pigmented layer non-visual part: covers ciliary body and iris Fundus posterior part with optic disc, macula lutea with fovea centralis Ora serrata optic part terminates
Eyelids Eyelids Conjunctiva Peri-orbital fat Fibrous attachments
Eyelids Orbital septum Palpebral ligaments
Lacrimal apparatus
Extra-ocular muscles Rectus muscles - Superior - Inferior - Medial - Lateral Superior oblique Inferior oblique (Levator palpebrae superioris)
Movements of the eye
Movements of the eye Superior oblique Inferior oblique Superior rectus Inferior rectus Medial rectus Lateral rectus Depression Intorsion, Abduction Elevation Extorsion, Abduction Elevation Adduction, Intorsion Depression Adduction, Extorsion Adduction Abduction Levator palpebrae superioris Elevation of upper eyelid
Innervation III IV VI V1 Lacrimal glands Eyelids VII (Greater petrosal n) Lacrimal glands Autonomic Sympathetic Deep petrosal n via plexus on ICA Parasympathetic Short ciliary nn from ciliary ganglion (III) (LR 6 SO 4 ) 3
Arterial supply Arterial supply from the ophthalmic branch of the internal carotid artery Facial artery joins the dorsal nasal branch of the ophthalmic artery Maxillary artery infra-orbital artery
Venous Drainage Venous drainage via superior and inferior ophthalmic veins Pterygoid venous plexus Facial vein and danger area Cavernous sinus
Visual pathway Optic radiations (Meyer s loop) Visual association cortex, areas 18 & 19 involve posterior temporal lobe (Wernicke)
Reflex pathway Constrictor pupillae Ciliary muscle Short ciliary nerves (postganglionic fibres) Optic nerve Ciliary ganglion CN III (preganglionic fibres) Substantia nigra Optic tract Red nucleus Lateral geniculate body Medial geniculate body Edinger-Westphal nucleus Pretectal area Brachium of superior colliculus Pulvinar of thalamus Superior colliculus Posterior commissure
Reflex pathway
Corneal reflex Any stimulus to the conjunctiva or cornea excites blinking. Afferent fibres travel via the ophthalmic division of the trigeminal nerve and synapse in the spinal tract and nucleus of CN V. Efferent impulses in branches of the facial nerve to orbicularis oculi. Patient not blinking: Either V1 or VII Test V1 on forehead to exclude
Accommodation reflex Pathways from visual cortex Pretectal area Fibres from III, IV and VI cause: (i) Vergence of the extra-ocular muscles via frontal eye fields (squint) (ii) Parasympathetic activation of the constrictor and ciliary muscles within each eye
Clinical applications
Trochlear nerve (IV) The patient is attempting to look down and to the left, but his movement is impaired in the right eye. The patient present with diplopia, especially when reading, and difficulty in walking downstairs.
Oculomotor nerve (III) Dense ptosis due to CN III lesion - eye rests in down and out position Parasympathetic component ciliary ganglion dilated pupil with lack of constriction sphincter pupillae = loss of normal pupillary reflex Loss of accommodation ciliary muscle
Abducent nerve (VI) Strabismus en diplopia Weakness or paralysis of ipsilateral lateral rectus cannot abduct past midline (LMN lesion) Several mechanisms: vascular (aneurysms, infarct in pons) 4 th ventricle (will also affect CN VII), infection (esp. in otitis media), skull-base fractures, cavernous sinus pathology
Sympathetic supply Horner s syndrome: (oculosympathetic paresis) Ipsilateral injury to cervical sympathetic trunk / T1 C8 Ptosis (partial) Miosis (parasymp) Facial anhidrosis
Facial nerve palsy Paralysis of orbicularis oculi closure of eyelids Ectropion turning outward of eyelid margin Movement of eye unaffected Lacrimation affected dry eye
Entropion Old age Spasm of orbicularis oculi
Hyphema http://www.eyeatlas.com Blood in the anterior chamber of the eye
Tumours Position: In ethmoid or sphenoid sinuses erodes orbital walls Compression of CN II Proptosis Tumour metasteses Middle cranial fossa Temporal / Infratemporal fossa superior orbital fissure inferior orbital fissure
Trauma Foreign object Retinal detachment http://www.oftalmo.com
Trauma Blowout fracture http://www.eyecasualty.co.uk Restricted left upgaze caused by orbital floor fracture. Displacement of orbital wall Unstable muscle attachments Medial wall: -Ethmoid -Sphenoid Floor: Maxillary sinus Proptosis: intra-ocular bleeding
Trauma Raccoon eyes Peri-orbital bruising, # frontal skull area, cavernous sinus thrombosis