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Ocular Anatomy Learning Objectives At the end of this class students shall be able to Identify various structures of the eye Have a basic understanding of the structure and functions of various parts of the eye Orbit Lodges the eyeball Eye lids Cover and protect Lacrimal system Secretes and drain tears Extraocular muscles for ocular movements Layers of eyeball perform various functions Bony Orbit Made by 7 Bones Frontal Zygomatic Maxillary Ethmoidal Sphenoid Lacrimal Palatine Frontal view of bony orbit Outer eye Eyelids The eyelids fulfill two main functions protection of the eyeball secretion distribution and drainage of tears The eyelid muscles Lid structure and movement The levator muscle extends from an attachment at the orbital apex to attachments at the tarsal plate and skin The lids are securely attached at either end to the bony orbital margin by medial and lateral palpebral ligaments Innervation Sensory innervation is from the trigeminal fifth cranial nerve via the ophthalmic division upper lid and maxillary division lower lid The orbicularis oculi is innervated by the facial seventh nerve The levator muscle in the upper lid is supplied by the oculomotor third nerve Blood supply Network of blood vessels which form an anastomosis between branches derived from the external carotid artery via the face and from the internal carotid artery via the orbit Lymphatics Lymphatic fluid drains into the preauricular and submandibular nodes Preauricular lymphadenopathy is a useful sign of infective eyelid swelling especially viral Lacrimal system Lacrimal gland Lacrimal passage Lacrimal puncta Lacrimal canaliculi Lacrimal sac Naso lacrimal duct Tear production The lacrimal gland secretes most of the aqueous component of the tear film Location superotemporal part of the anterior orbit Innervation parasympathetic fibres carried by the facial nerve Lacrimal Apparatus Drainage system Extraocular muscles 4 Recti 2 Obliques Medial rectus MR Inferior Rectus IR Superior rectus SR Inferior oblique IO Superior Oblique SO Lateral Rectus LR Extra ocular muscles Action results in eye movements Medial Rectus Adduction Inferior Rectus Depression Extorsion Adduction Superior Rectus Elevation Intorsion Adduction Inferior Oblique Extorsion Elevation Abduction Superior Oblique Intorsion Depression Abduction Lateral Rectus Abduction EXTRAOCULAR MUSCLES Nerve supply of Extra Ocular Muscles Three Cranial Nerves supply the Extra Ocular Muscles CN 3rd Oculomotor MR IR SR IO CN 4th Trochlear SO CN 6th Abducens LR Overview of ocular anatomy Conjunctiva The conjunctiva is a mucous membrane lining the eyelids Covers the anterior eyeball up to the edge of the cornea At the upper and lower reflections between eyeball and eyelid conjunctiva forms two sacs the superior and inferior fornices Cornea and sclera The cornea and sclera form a spherical shell which makes up outer wall of eyeball Cornea and sclera The sclera is principally collagenous avascular apart from some vessels on its surface relatively acellular It is perforated posteriorly by the optic nerve and by sensory and motor nerves and blood vessels to the eyeball The cornea and sclera merge at the corneal edge the limbus Limbus Juncture between the cornea and the sclera Nourishes peripheral cornea Assists in corneal wound healing Pathway for aqueous outflow contains trabecular meshwork and canal of schlemm Corneoscleral limbus Transition zone anterior bowman s terminal Descemet s terminal posterior scleral spur iris root 1 5 2 0mm width Appearance Semitransparant zone White sclera Angle of AC The chief functions of the cornea Protection against invasion of microorganisms into the eye Transmission and focusing refraction of light Cornea Made up of 5 layers Specialized Transparent Tissue No blood vessels Primarily responsible for refracting light 43 44 diopters More nerve endings than anywhere else in the body Protection to the eye The only part of the eye that is transplanted from one person to another Cornea Epithelium Bowman membrane Stroma Descemet membrane posterior limiting layer of cornea Endothelium Cornea 5 layered Cornea Oval transverse 11 5 12mm vertical 10 5 11mm curvature anterior 7 8mm posterior 6 8mm thickness centre 0 5 0 55mm periphery 1mm Refractive index 1 377 Cornea 1 Epithelium 50 m 5 6 layers Squamous cell Basal cell Renewing cycle 7 days 2 Bowman s membrane 12 m No cell Collagen matrix Scar Cornea 3 Stroma 4 Descemet s membrane 500 m 2 3 corneal cells 1 matrix GAGs Fibrous lamina 200 250 layers Parallel to surface Parallel collagen fibers Ordered arrangement Scar 10 12 m No structure elasticity Secreted by endothelial cells Basal membrane of endothelial cell Regeneration Cornea 5 Endothelium 5 m Monolayer hexagon 500 000 cells Tight junctions Pump UVEA The uvea comprises the iris and ciliary body anteriorly choroid posteriorly Iris Consists of connective tissue containing muscle fibres blood vessels and pigment cells Its posterior surface is lined by a layer of pigment cells At its centre is an aperture the pupil The main function of pupil Control light entry to the retina and to reduce intraocular light scatter Ciliary body The ciliary body is a specialised structure uniting the iris with the choroid Secretes aqueous humour Anchors the lens via the zonules through which it modulates lens convexity The posterior part of the ciliary body merges into the retina at the ora serrata Choroid The choroid consisting of blood vessels connective tissue and pigment cells is sandwiched between the retina and the sclera It provides oxygen and nutrition to the outer retinal layers Lens The discus like lens comprises a mass of long cells known as fibres Has a hard nucleus surrounded by less dense fibres the cortex Relatively dehydrated Transparent Aqueous humour Fills the anterior and posterior chambers The anterior chamber is the space between the cornea and the iris Behind the iris and in front of the lens is the posterior chamber They are connected by the pupil Formation The ciliary body forms aqueous humour By ultrafiltration and active secretion Drainage Aqueous circulates from the posterior to the anterior chamber through the pupil Passes through the trabecular meshwork a specialised tissue in the anterior chamber angle between the iris and the cornea From here aqueous drains into Schlemm s canal Vitreous A thick transparent gel like substance that fills the center of eyeball giving it form and shape The vitreous body is 99 water but vitally


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ASHS ANAT 05 - Ocular Anatomy

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