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Anatomy & Development of The ANATOMY & DEVELOPMENT OF THE EYE PRESENTED BY Geetanjali Miglani MSN, RN, RM EYEBALL ■ Shape – Although, generally referred to as a globe, the eyeball is not a sphere but an ablate spheroid, consisting of two modified spheres fused together. Cornea is a part of the anterior smaller sphere with a radius of about 7.8 mm and sclera is a part of the posterior larger sphere with a radius of about 12 mm. ■ Poles – The central point on the maximal convexities of the anterior and posterior curvatures of the eyeball is called the anterior and posterior pole, respectively. ■ Equator of the eyeball lies at the mid plane between the two poles GEETANJALI MIGLANI 2 GEETANJALI MIGLANI 3 COATS OF THE EYEBALL The eyeball comprises three coats: outer (fibrous coat), middle ( vascular coat) and inner (nervous coat) ■ Fibrous coat – It is a dense strong wall which protects the intraocular contents. Anterior l/6th of this fibrous coat is transparent and is called cornea. Posterior 5/6th opaque part is called sclera. Cornea is set into the sclera like a watch glass. Junction of the cornea and sclera is called limbus. Conjunctiva is firmly attached at the limbus. GEETANJALI MIGLANI 4 ■ Vascular coat (uveal tissue) – It supplies nutrition to the various structures of the eyeball. It consists of three parts, from anterior to posterior, which are: iris, ciliary body and choroid. ■ Nervous coat (retina) – It is concerned with visual functions and projects co visual cortex through the visual pathway. GEETANJALI MIGLANI 5 SEGMENTS AND CHAMBERS OF THE EYEBALL The eyeball can be divided into two segments: anterior and posterior. 1. ANTERIOR SEGMENT: It includes crystalline lens (which is suspended from the ciliary body by zonules), and structures anterior to it, such as iris, cornea and two aqueous humour-filled spaces: anterior and posterior chambers. GEETANJALI MIGLANI 6 Anterior Chamber ■ It is bounded anteriorly by the back of cornea, and posteriorly by the anterior surface of iris and part of ciliary body. ■ The anterior chamber is about 2.5 mm deep in the center in normal adults. It is slightly shallower in hypermetropes and deeper in myopes. but is almost equal in the two eyes of the same individual. ■ It contains about 0.25 mL of the aqueous humour. It communicates with posterior chamber through the pupil. GEETANJALI MIGLANI 7 Posterior chamber ■ It is a triangular space containing 0.06 mL of aqueous humour. It is bounded anteriorly by the posterior surface of iris and part of ciliary body, posteriorly by the crystalline lens and its zonules, and laterally by the ciliary body. GEETANJALI MIGLANI 8 2. POSTERIOR SEGMENT: lt includes the structures posterior to lens, viz., vitreous humour (a gel-like structure which fills the space behind the lens), retina, choroid and optic disc. GEETANJALI MIGLANI 9 VISUAL PATHWAY ■ Each eyeball acts as a camera; it perceives the images and relays the sensations to the brain (occipital cortex) via visual pathway which comprises optic nerves, optic chiasma, optic tracts, geniculate bodies and optic radiations. GEETANJALI MIGLANI 10 ORBIT AND EXTRAOCULAR MUSCLES ■ BONY ORBIT – Each orbit is a quadrilateral pyramid shaped bony cavity, in which the eyeball is located in the anterior part, nearer to the roof and lateral wall than to the floor and medial wall ■ EXTRAOCULAR MUSCLES – Six in number on each side, control movements of the eyeball. GEETANJALI MIGLANI 11 APPANDAGES OF THE EYES These are essential for normal working of the eyeball include: ■ Eyelids: – These form the shutters which protect the eyeballs anteriorly. ■ Conjunctiva: – It is a thin translucent mucous membrane which lines the posterior surface of the eyelids and the anterior part of the sclera. ■ Lacrimal apparatus: – It comprises lacrimal glands, (which produce tears to keep the cornea and conjunctiva moist for smooth functioning) and lacrimal passages (which drain the continuously formed tears). GEETANJALI MIGLANI 12 BLOOD VESSELS ARTERIES VEINS ■ Ophthalmic artery, a Veins draining blood from the branch of internal carotid eyeball include: artery, constitutes the main source of blood ■ Central retinal vein- which supply for the eyeball and drains blood from the retina other orbital structures. Blood supply of each ■ Anterior ciliary veins, short ocular structure is posterior ciliary veins and described in the relevant venae verticosae- which drain chapters. blood from the uveal tissue. GEETANJALI MIGLANI 13 BRANCHES OF OPTHALMIC ARTERY OCULAR GROUP ORBITAL GROUP • Central retinal • Lacrimal artery artery • Recurrent • Long posterior meningeal artery ciliary arteries • Supraorbital • Short posterior artery ciliary arteries • Medial palpebral • Muscular artery branches • Posterior ethmoidal artery • Anterior ethmoidal artery • Dorsal nasal artery • Supratrochlear artery GEETANJALI MIGLANI 14 NERVES SENSORY NERVES MOTOR NERVES ■ Ophthalmic Nerve ■ 3rd Cranial Nerve i. Lacrimal Nerve (Occulomotor) ii. Frontal Nerve ■ 4th Cranial Nerve iii. Nasociliary Nerve (Trigeminal) ■ 6th Cranial Nerve (Abducens) ■ 7th Cranial Nerve (Facial) GEETANJALI MIGLANI 15 GEETANJALI MIGLANI 16 DEVELOPMENT OF THE EYE GEETANJALI MIGLANI 17 DEVELOPMENT OF THE EYE Development of the eyeballs can he considered to commence around day 22 when the embryo has eight pairs of so mites and is around 2 mm in length. GEETANJALI MIGLANI 18 ■ Eyeball and its related structures are derived from the following primordia: – Optic vesicle: an outgrowth from pros encephalon (a neuroectodermal structure) – Lens placode: a specialized area of surface ectoderm, and the surrounding surface ectoderm. – Mesenchyme surrounding the optic vesicle. GEETANJALI MIGLANI 19 FORMATION OF OPTIC VESICLE AND OPTIC STALK ■ The area of neural plate (Fig-A) which forms the pros-encephalon develops a linear thickened area on either side (Fig- B) ■ Which soon becomes depressed to form the optic sulcus (Fig-C). ■ As the optic sulcus deepens, the walls of the pros-encephalon overlying the sulcus bulge out to form the optic vesicle (Figs-D, E & F). ■ The proximal part of the optic vesicle becomes constricted and elongated to form the optic stalk (Figs-G and H) GEETANJALI MIGLANI 20 FORMATION OF LENS VESICLE ■ The optic vesicle grows laterally and comes in contact with the surface ectoderm. ■ The surface ectoderm, overlying the optic vesicle becomes thickened to form the lens placode, which sinks below the surface and is converted into the lens vesicle. ■ It is soon separated from the surface ectoderm at 33rd day of gestation GEETANJALI MIGLANI 21 FORMATION OF OPTIC CUP ■ During embryonic development of the eye, the outer wall of the bulb of the optic vesicles becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup. GEETANJALI MIGLANI 22 GEETANJALI MIGLANI 23 MESENCHYME ■ The developing neural tube (from which central nervous system develops) is surrounded by mesenchyme, which subsequently condenses to form meninges. ■ An extension of this mesenchyme also covers the optic vesicle. ■ This mesenchyme differentiates to form a superficial fibrous layer (dura) and a deeper vascular layer (pia- arachnoid). GEETANJALI MIGLANI 24 GEETANJALI MIGLANI 25 OTHER OCULAR STRUCTURES RETINA ■ Retina is developed from the two walls of the optic cup, namely- Nervous retina from the inner wall, and Pigment epithelium from the outer wall GEETANJALI MIGLANI 26 ■ OPTIC NERVE – The optic nerve is derived from optic stalks during the seventh week of development. ■ CRYSTALLINE LENS – The crystalline lens is developed from the surface ectoderm ■ CORNEA – This is also developed from surface ectoderm GEETANJALI MIGLANI 27 ■ SCLERA – Sclera is developed from the fibrous layer of mesenchyme surrounding the optic cup. ■ IRIS – The iris develops from both layers of the optic cup. The outer layer of optic cup forms the pigmented layer of the iris. The inner layer of optic cup forms the non-pigmented layer of the iris. GEETANJALI MIGLANI 28 EYELIDS ■ Eyelids are formed by reduplication of surface ectoderm above and below the cornea. ■ The folds enlarge and their margins meet and fuse with each other. ■ The lids cut off a space called the conjunctival sac. GEETANJALI MIGLANI 29 ■ Conjunctiva – Conjunctiva develops from the ectoderm lining the lids and covering the globe. GEETANJALI MIGLANI 30 AUTONOMIC NERVES GEETANJALI MIGLANI 31 PARASYMPATHETIC NERVES ■ Edinger-Westphal Nucleus, located in midbrain, sends: – Preganglionic fibers through the third cranial nerve to ciliary ganglion and accessory ganglion. – Postganglionic nerve fibers from ciliary ganglion travel along the short ciliary nerves to supply the sphincter pupillae muscle and postganglionic fibers from the accessory ganglion supply the ciliary muscleGEETANJALI. MIGLANI 32 ■ Lacrimal Nucleus, located in pons, sends: – Preganglionic fibers through facial nerve to the sphenopalatine ganglion. – Postganglionic secretomotor fibers finally reach the lacrimal gland through the lacrimal nerve. GEETANJALI MIGLANI 33 SYMPATHETIC NERVES ■ Preganglionic fibers arise from the cilio-spinal center of Budge and go to cervical sympathetic chain to relay in the superior cervical ganglion. ■ Postganglionic fibers from the superior cervical ganglion enter the skull with the internal carotid plexuses and supply following structures: – Orbital artery – Dilator pupillae muscle – Blood vessels inside the eyeball – Muscles of eyelid GEETANJALI MIGLANI 34 THANK YOU GEETANJALI MIGLANI 35.
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