RIMT UNIVERSITY SCHOOL OF PHYSIOTHERAPY BACHELOR OF PHYSIOTHERAPY STUDY MATERIAL Topic: Anatomy Of Eye Provided By: Dr Ambuja Bhardwaj (PT) Subject: HUMAN ANATOMY II Subject code: BPT1201 Anatomy of Eye Introduction 1. The three coats of the eye are as follows: (a) Outer fibrous layer: The eye is the primary organ of vision. Each one • cornea of the two eyeballs is located in the orbit, where • sclera it takes up about one-fifth of the orbital volume • lamina cribrosa. (Figure 2.1). The remaining space is taken up (b) Middle vascular layer (“uveal tract”): by the extraocular muscles, fascia, fat, blood vessels, nerves and the lacrimal gland. •iris The eye is embryologically an extension of • ciliary body – consisting of the pars the central nervous system. It shares many plicata and pars plana common anatomical and physiological proper- • choroids. ties with the brain. Both are protected by bony (c) Inner nervous layer: walls, have firm fibrous coverings and a dual • pigment epithelium of the retina blood supply to the essential nervous layer in • retinal photoreceptors the retina. The eye and brain have internal cav- • retinal neurons. ities perfused by fluids of like composition and under equivalent pressures. As the retina and 2. The three compartments of the eye are as optic nerve are outgrowths from the brain, it is follows: not surprising that similar disease processes (a) Anterior chamber – the space between affect the eye and central nervous system. The the cornea and the iris diaphragm. physician should constantly remind himself or (b) Posterior chamber – the triangular space herself of the many disease conditions that can between the iris anteriorly, the lens and simultaneously involve the eye and the central zonule posteriorly, and the ciliary body. nervous system. (c) Vitreous chamber – the space behind the lens and zonule. 3. The three intraocular fluids are as follows: Basic Structure of the Eye and (a) Aqueous humour – a watery, optically Supporting Structures clear solution of water and electrolytes similar to tissue fluids except that The Globe aqueous humour has a low protein content normally. The eye has three layers or coats, three com- (b) Vitreous humour – a transparent gel partments and contains three fluids (Figure 2.2). consisting of a three-dimensional 7 8 Common Eye Diseases and their Management Upper palpebral furrow Mucocutaneous junction Cornea Iris Ciliary body Conjunctiva Upper punctum Sclera Caruncle Choroid Retina Lower punctum Openings of tarsal glands Figure 2.2. Layers of the globe. Semilunar folds Figure 2.1. Surface anatomy. sixths are formed by the sclera and lamina cribrosa. The cornea is transparent, whereas the sclera, which is continuous within it, is white. network of collagen fibres with the The junction of cornea and sclera is known as interspaces filled with polymerised the limbus. The cornea has five layers antero- hyaluronic acid molecules and water. It posteriorly (Figure 2.3): fills the space between the posterior surface of the lens, ciliary body and 1. Epithelium and its basement membrane – retina. stratified squamous type of epithelium (c) Blood – in addition to its usual func- with five to six cell layers of regular tions, blood contributes to the main- arrangement. tenance of intraocular pressure. Most 2. Bowman’s layer – homogeneous sheet of of the blood within the eye is in the modified stroma. choroid. The choroidal blood flow rep- 3. Stroma – consists of approximately 90% resents the largest blood flow per unit of total corneal thickness. Consists of tissue in the body. The degree of lamellae of collagen, cells and ground desaturation of efferent choroidal substance. blood is relatively small and indicates 4. Descemet’s membrane – the basement that the choroidal vasculature has membrane of the endothelium. functions beyond retinal nutrition. It 5. Endothelium – a single layer of cells lining might be that the choroid serves as a the inner surface of Descemet’s membrane. heat exchanger for the retina, which absorbs energy as light strikes the retinal pigment epithelium. Clinically, the eye can be considered to be Epithelium composed of two segments: Bowman’s membrane 1. Anterior segment – all structures from (and including) the lens forward. 2. Posterior segment – all structures post- Stroma erior to the lens. The Outer Layer of the Eye Descemet’s membrane Endothelium The anterior one-sixth of the fibrous layer of the eye is formed by the cornea. The posterior five- Figure 2.3. The cornea. Basic Anatomy and Physiology of the Eye 9 In the region of the limbus, the epithelium on of the triangle (mainly ciliary muscles) lies the outer surface of the cornea becomes con- against the sclera. The inner side is divided into tinuous with that of the conjunctiva, a thin, two zones: (1) the pars plicata forms the ant- loose transparent nonkeratinising mucous erior 2mm and is covered by ciliary processes membrane that covers the anterior part of the and (2) the pars plana constitutes the posterior sclera, from which it is separated by loose con- 4.5-mm flattened portion of the ciliary body. nective tissue.Above and below, the conjunctiva The pars plana is continuous with the choroid is reflected onto the inner surface of the upper and retina. and lower lids. This mucous membrane, there- The choroid consists of the following: fore, lines the posterior surface of the eyelids • Bruch’s membrane – membrane on the and there is a mucocutaneous junction on the external surface of the retinal pigment lid margin. Although the conjunctiva is con- epithelium (RPE). It consists of the base- tinuous,it can be divided descriptively into three ment membrane of RPE cells and chorio- parts: palpebral (tarsal), bulbar and fornix. capillaris. Between the two layers of The sclera consists of irregular lamellae of basement membrane are the elastic and collagen fibres. Posteriorly, the external two- collagenous layers. Small localised thick- thirds of the sclera become continuous with the enings of Bruch’s membrane (which dural sheath of the optic nerve, while the inner increase with age) are called drusen. one-third becomes the lamina cribrosa – the fenestrated layer of dense collagen fibres • The choriocapillaris – a network of capil- through which the nerve fibres pass from the laries supplying the RPE and outer retina. retina to the optic nerve. The sclera is thickest • Layer of larger choroidal blood vessels posteriorly and thinnest beneath the insertions external to the choriocapillaris. of the recti muscles. There is a layer of loose • Pigmented cells scattered in the choroid connective tissue deep to the conjunctiva, over- external to the choriocapillaris. lying the sclera, called the episclera. Inner Layer Middle Layer The inner layer of the eye, which lines the vas- The middle layer is highly vascular. If one were cular uvea, is the neurosensory layer. This layer to peel the sclera away from this layer (not an forms the retina posteriorly; but, anteriorly it easy task), the remaining structure would comes to line the inner surface of the ciliary resemble a grape, as this middle layer, which is body and iris as a two-layered pigment epithe- called the uvea, is heavily pigmented as well as lium. These same layers can be traced into the being vascular. The anterior part of the uvea retina, which is composed of an outer pigment forms the bulk of the iris body and hence epithelium and an inner sensory part, which inflammation of the iris is called either anterior contains the rods and cones, bipolar cells and uveitis or iritis. The posterior part of the uvea is ganglion cells (Figure 2.4). The junction of the called the choroid. retina and the pars plana forms a scalloped The iris is the most anterior part of the uvea. border known as the ora serrata. It is a thin circular disc perforated centrally It is important to note that the photoreceptor by the pupil. Contraction of the iris sphincter cells are on the external side of the sensory muscle constricts the pupil, while contraction of retina. The relationship of the retinal elements the dilator pupillae muscle dilates the pupil. can be understood most readily by following the The ciliary body is part of the uveal tissue and formation of the optic cup. As the single-cell is attached anteriorly to the iris and the scleral layer optic vesicle “invaginates”to form the two- spur; posteriorly it is continuous with the cell layered optic cup, the initially superficial choroid and retina. The ciliary body is also cells become the inner layer of the cup. The RPE referred to as the intermediate uvea. develops from the outer layer of the cup, facing The ciliary body is triangular in cross- the photoreceptors across the now obliterated section. The anterior side of the ciliary body is cavity of the optic vesicle. The neurons of the the shortest and borders the anterior chamber sensory retina differentiate from the inner layer angle; it gives origin to the iris. The outer side of the optic cup. 10 Common Eye Diseases and their Management Ganglion cells Bipolar cells Lacrimal gland Lacrimal artery Rods and cones Long posterior ciliary artery Optic nerve Pigment epithelium Ophthalmic artery Choroid Internal carotid artery Figure 2.4. The retina. Figure 2.5. Blood supply of the eye. Optic Nerve The optic nerve meets the posterior part of the Blood Supply globe slightly nasal to the posterior pole and slightly above the horizontal meridian. Inside The blood supply of the globe is derived from the eye this point is seen as the optic disc. There three sources: the central retinal artery, the are no light-sensitive cells on the optic disc – anterior ciliary arteries and the posterior ciliary and hence the blind spot that anyone can find in arteries.