Eye and orbit LA BDS ho.pdf

The Eye and Orbit Laura Andreae The orbit The orbit (right eye) Superior wall nose The orbit (right eye) Medial wall (thin) nose The orbit (right eye) Lateral wall - thick nose The orbit (right eye) nose Inferior wall (floor) - thin Orbit: relation to surrounding sinuses Frontal sinus Ethmoid...

The Eye and Orbit Laura Andreae The orbit The orbit (right eye) Superior wall nose The orbit (right eye) Medial wall (thin) nose The orbit (right eye) Lateral wall - thick nose The orbit (right eye) nose Inferior wall (floor) - thin Orbit: relation to surrounding sinuses Frontal sinus Ethmoid sinus Maxillary sinus Blowout fractures of the orbit Suspensory ligament Eyeball is embedded in orbital fat and supported by a hammock-like suspensory ligament eye What protects the eye? – eyelids, tears, conjunctiva What protects the eye? – eyelids, tears, conjunctiva What protects the eye? – eyelids, tears, conjunctiva What protects the eye? – eyelids, tears, conjunctiva Production of lacrimal fluid (tears) is stimulated by parasympathetic impulses from CN VII and secreted through lacrimal ducts to surface of conjunctiva. When the eyelids blink (come together lateral to medial sequence) this pushes the fluid medially over the cornea. Fluid containing foreign material is pushed to the medial angle of the eye and drains through lacrimal canaliculi (begin at lacrimal puncta) into lacrimal sac (dilated part of nasolacrimal duct near top). Nasolacrimal duct conveys fluid to nasal cavity. Muscles of eyelid Levator palpebrae superioris muscle only in upper eyelid – raises eyelid (innervation CN III), inserts into tarsus. Also in companion with levator palpebrae superioris is a collection of smooth muscle fibres - superior tarsal muscle (some call it part of lev palp sup) - also raises eyelid (innervation sympathetic fibres from sup cervical ganglion). Loss of function of either lev palp sup (eg CN III lesion) or sup tarsal (eg sympathetic lesion) => ptosis (drooping eyelid) Muscles of eyelid Orbicularis oculi muscle Palpebral part of orbicularis oculi close eyelids during sleep and blinking, rest of muscle used to screw eyes tightly shut for protection. Damage to facial nerve (CN VII) leads to paralysis, preventing eyelids from closing fully and eversion of lower eyelid, which in turn can cause drying and damage to the cornea The eyeball Eyeball has 3 layers: sclera choroid retina Sclera – dense and white, continuous with transparent cornea Choroid – pigmented and highly vascular, continuous with ciliary body and iris Retina – light sensitive, neural part of eye Choroid and ciliary body Choroid is dark red-brown layer – pigmented and highly vascular (highest perfusion rate per gram in whole body), responsible for ‘red eye’ in flash photos. Choroid Ciliary body Continuous with ciliary body – ring like thickening, muscular and vascular, provides attachment for lens. Ciliary process – secretes aqueous humour. The iris lies on the anterior surface of lens and is a thin contractile diaphragm with a central aperture – pupil – for transmitting light. Pupil Two involuntary muscles control size of pupil: Dilator pupillae – radially arranged, sympathetic innervation Dilator pupillae Sphincter pupillae Sphincter pupillae – circularly arranged, parasympathetic innervation Dilator pupillae Sphincter pupillae Accommodation Ciliary muscle controls shape of lens and therefore focus Ciliary muscle Lens Zonules of Zinn! To focus on near objects, ciliary muscles contract (parasym, III) => release tension in zonal fibres => lens rounder. Increased curvature of lens means focal point shifts closer to eye Extra-ocular muscles Extra-ocular muscles 6 extra-ocular muscles move eyeball: Lateral view Superior view Extra-ocular muscles 2 pairs of recti: lateral and medial rectus Medial rectus Medial rectus Lateral rectus Lateral rectus Lateral view Superior view Extra-ocular muscles 2 pairs of recti: lateral and medial rectus, and superior and inferior rectus Superior rectus Superior rectus Inferior rectus Lateral view Superior view Extra-ocular muscles 1 pair of obliques: superior and inferior oblique Superior oblique Superior oblique Inferior oblique Lateral view Superior view Extra-ocular muscles Coronal MRI through the eye Extra-ocular muscles Extra-ocular muscles - innervation CN IV All other muscles: CN III (oculomotor) Superior oblique LR6SO4 CN VI Lateral rectus Lateral view Autonomic innervation Ciliary ganglion Sensory fibres Sympathetic fibres Parasympathetic preganglionic fibres Parasympathetic postganglionic fibres Superior orbital fissure and optic canal Superior orbital fissure Optic canal II Superior orbital fissure and optic canal V1 – frontal branch V1 – lacrimal branch Superior orbital fissure VI IV II Optic canal Opthalmic artery Sup branch of III V1 – nasociliary branch Inf branch of III The orbit: blood supply Optic nerve Central artery of retina Opthalmic artery Internal carotid artery The orbit: venous drainage Supra-orbital vein Cavernous sinus Suggested reading and sources The Head and Neck: Dean and Pegington (Volume 3, chapter 2) Gray’s Anatomy for Students: Drake et al Essential Clinical Anatomy: Moore et al