Eye Anatomy PDF

Okay, here is the converted text from the images/document you sent, formatted in Markdown. # Organs of special senses ## The eye The eye is a highly specialized organ for vision & photoreception. It permits an accurate analysis of the form, intensity & color of light reflected from objects. ###...

Okay, here is the converted text from the images/document you sent, formatted in Markdown. # Organs of special senses ## The eye The eye is a highly specialized organ for vision & photoreception. It permits an accurate analysis of the form, intensity & color of light reflected from objects. ### Location The human eye ball is about 24 mm in diameter. It is located in the orbit of skull & protected anteriorly by eyelids. ### Oculomotor Muscles Here is a description of an image of the eye and the oculomotor muscles: * superior Olique * Superior Rectus * Medial Rectus * Lateral Rectus * Inferior Rectus * Inferior Oblique Extraocular muscles allow the eye to move within its orbit as a conjugate gaze for both eyes; the eyes move symmetrically (in the same direction at the same time). ## Structure of the eye Each eyeball includes: * a tough, fibrous globe to maintain its shape * a system of transparent tissues that refract light to focus the image * a layer of photosensitive cells, & a system of neurons to collect, process, and transmit visual information to the brain Here is an description of diagram of the structure of the eye: * **Fibrous tunic** * Sclera * Cornea * **Vascular tunic** * Iris * Ciliary body * Choroid * **Retina** * Pigmented layer * Neural layer The eye contains 3 compartments: * Anterior chamber, which contains aqueous humor * Posterior chamber * Vitreous space, contains Vitreous humor Here is an description of diagram of the structure of the eye: * Sclera * Anterior chamber * Cornea * Vitreous space * Aqueous humor * Vitreous humor * Posterior Chamber * Lens * Iris * Ciliary body * Choroid * Retina * Optic nerve ### Sclera * Posterior 5/6 of the external layer * Opaque & white, relatively avascular * Consists of dense CT: * Collagen type I bundles * Ground substance * Fibroblasts Here is a description of an image of Sclera: Tenon's capsule surrounds the eye ball. Tenon's space is between episclera & tenon's capsule (rotating movement). * Tenon's fascia * Sclera * Tenon's space * Muscle * Cellular tissue * Optic nerve ### Cornea * Anterior 1/6 of the external layer * It is convex anteriorly (dome shaped) * Colorless, transparent & sensitive * Avascular, can be successively transplanted * Function: * Refract light onto the lens (focusing), due to its transparency & curvature * Protection ### Structure of the cornea * Consists of 5 layers: (3 cellular layers separated by 2 a cellular layers) * Epithelium * Bowman's membrane * Stroma (substantia propria) * Descemet's membrane * Endothelium Here is a description of an image of Structure of the cornea: * anterior corneal epithelium stratified squamous * keratocyte nuclei * corneal stroma * posterior limiting lamina * posterior endothelium #### 1. Epithelium of the cornea * Stratified squamous non keratinized * Formed of 5-6 layers of cells * The surface cells joined by tight junctions * Cells of other layers connected by desmosomes * Thick basement membrane for stability & protection against infection * Basal cells responsible for regeneration & turn over (7 days) #### Protective adaptations of corneal epithelium * Surface cells provided by microvilli protruding in space filled with Precorneal tear film of lipids, glycoprotein & water which keep cornea wet & prevent ulceration * Absorb oxygen & nutrients from the tear film * Have rich sensory nerve supply * Stimulation of nerves lead to blinking of eye lid & flowing of tears * Surface cells connected by tight junction #### 2. Bowman's membrane anterior limiting membrane * The basement membrane of the stratified epithelium * Consists of randomly arranged collagen I fibers * Has no cells * Contributes to stability & strength * Can not be regenerated #### 3. Stroma (substantia propria) * Thick layer (90%) of the cornea thickness * Consists of parallel lamella of collagen fibrils * Collagen fibers within each layer will run parallel to each other but at right angles to the fibers in the next layer * Flattened fibroblasts (keratocytes) like the wings of butterfly between the bundles * Ground substance rich in glycoproteins & chondroitin sulfate #### 4. Decemet's membrane posterior limiting membrane * The basement membrane of the endothelium * Thick & homogenous * Fine collagen (VIII) filaments arranged in three dimensional net work #### 5. Endothelium * Simple squamous epithelium * Connected by tight junction * Possess characteristic of active transport & protein synthesis cells * Have limited proliferative potential(can not regenerate) * Function: * to keep the cornea clear by pumping the excess Fluid out of the stroma (active transport of $Na^+$ & $Cl^-$) * Endothelium function in maintaining the transparency of the cornea through the dehydration of the stroma * Forms Descemet's membrane * This provide maximum transparency and optimal light refraction ### Transparency of the cornea * Due to: * Avascular * Dehydration state (low water content) * Regular parallel arrangement of collagen fibrils ( destructive interference ) *Fibrils & ground substance have the same refractive index *Clinically * The shape or curvature of the cornea can be changed surgically to improve certain visual abnormalities involving the ability to focus * In laser-assisted in situ keratomileusis (LASIK) surgery, the stroma reshaped by an excimer laser which vaporizes collagen and keratocytes in a highly controlled manner with no damage to adjacent cells or ECM ### Corneo-scleral junction (limbus) * It is transition zone between the cornea & sclera * Highly vascularized, supplies the cornea by diffusion * Contains the Schlemm's canal which drains the aqueous humor from the anterior chamber to the venous system Here is a description of an image of Corneal-Scleral Junction: aqueous humor has an inorganic ion composition similar to that of plasma but contains less than 0.1% protein (plasma has about 7% protein) * Drainage canal * Flow of aquesous fluid ### Changes at the limbus * Corneal epithelium continuous with the epithelium of bulbar conjunctiva * Bowman's membrane terminates * Corneal stromal collagen fibers loses its regularity * Descemet's membrane and its simple endothelium are replaced with a system of irregular endothelium-lined channels called the trabecular meshwork which penetrate the stroma and allow slow, continuous drainage of aqueous humor from the anterior cavity Here is a description of an image of Corneal-Scleral Junction: * outside world * cornea * epi thel i um of conjunctiva * outer sulcus of limbus * bul bar conjunctiva * limbus (sclerocorneal junction) * Sclera * ciliary body * ciliary muscle * fibers of suspensory ligament (zonule) * Schlemm's canal * trabecular meshwork * anterior chamber * iris * posterior chamber * ciliary process ### Flow of aqueous humor Schlemm's canal (scleral venous sinus) in the stroma receives aqueous humor from the trabecular meshwork & drains into the aqueous and episcleral veins of the sclera (venous system) Here is a description of the Aqueous Humour Pathway: * Trabecular meshwork (absorbs aqueous humour) * Canal of Schlemm (collects aqueous humour from trabecular meshwork) * Cornea * Conjunctiva * Ciliary m. (M3 accomodation). * Ciliary process (→ produces aqueous humour) * Arrows denote aqueous flow * Sclera * Lens * Anterior chamber * Dilator/radial m. (o, mydriasis) * Sphincter/ circular/ constrictor m.( M3 miosis) * Posterior chamber #### Clinical application Removal of aqueous humor is of major importance in regulating intraocular pressure. Factors causing impaired aqueous removal lead to glaucoma, a condition in which elevated pressure affects proper function of the retina and vision. ### Nutrition of the cornea * Cornea receives its nutrients by diffusion from aqueous humor (for the central part) & scleral vessels (for the peripheral part) * Cornea obtains oxygen directly from the air & tear film ### **2. Middle (vascular) layer the uveal tract (uvea)** * Consists of 3 parts, from posterior to anterior: 1. Choroid 2. Ciliary body 3. Iris ### 1. Choroid * Highly vascular coat * It is made up of 4 layers from outer to inner: Suprachoroidal lamina which is Loose CT rich in melanocytes bound to the sclera. Two vascular layers (large & medium vessels) Inner layer is Choriocapillary layer richer than the outer layer in small BVs which nourishes the retina. Bruch's membrane (hyaline membrane) separates the choriocapillary layer from retina. * Bruch's membrane is acellular & semipermeable * Bruch's membrane made up of 5 layers: * Basal lamina of choriocapillary endothelial cells * 2 layers of collagen fibers * Central layer of elastic fibers sandwiched between them * Basal lamina of retinal pigment epithelium The abundant melanocytes give the choroid its characteristic black color & block light from entering the eye except through the pupil. Here is the description of the diagram of Choroid histology; * A. * Sclera * Suprachoroid * Large vessels * Medium vessels * Choriocapillaris * Bruch's membrane * B. * Stroma * Retinal pigment epithelium * HL * SL * CC * RPE ### 2. Ciliary body * It is an anterior expansion (thickened ring) of the choroid at the level of lens * It is triangle in shape the Here is the description of the diagram of Eye; * Cornea * Canal of Schlemm * Sclera * Arterior chamber * Dilatar * Sphincter (M) * Lens * Posterior cavity * Ciliary body * Angle * Scleral venous sinus * Posterior Anterior cavity cavity * chamber chamber * (contains (contains * aqueous chamber humor) * Iris Clary epithelium Its long base contacting the sclera, another side in contact with the vitreous body, and the third facing the posterior chamber #### Histological structure of ciliary body * The bulk of ciliary body is formed of smooth muscles surrounded by stroma of loose connective tissue, rich in microvasculature, elastic fibers, and melanocytes * In cross section it is composed of 4 layers from internal to external: 1. Double layered epithelium 2. Stroma 3. Ciliary muscles 4. Supraciliary layer = layer of collagen fibers #### Structure of ciliary body * The inner surface of the ciliary body covered by 2 layers of epithelium: 1. inner pigmented is simple columnar cells rich in melanin, this is directly adjacent to ciliary body (corresponds to the pigment layer of retina) 2. outer non-pigmented )_covers the first; the surface layer facing the posterior chamber (derived from sensory layer of retina) #### Ciliary processes * Extensions of ciliary body * Core of CT tissue & fenestrated capillaries * Covered by the 2 layers of epithelium that cover the ciliary body * Zonule fibers or suspensory ligament (fibrillin & elastin) extend from these processes & insert into the capsule of the lens * The lens is anchored within the lumen of the ciliary body by this circular system of zonular fibere Here is the description of the diagram of Ciliary processes: * Comea Dilator Constrictor Iris muscle muscle * Pathway for aqueous humour Canal of Schlemm Ciliary muscle Suspensory Ciliary Ciliary ligaments Lens body #### Ciliary muscles * Arranged in 3 directions: * Meridional (longitudinal) fibers * Radial fibers * Circular fibers at the inner edge of ciliary body Here escription of the Ciliary muscles: * The ciliary muscles are important in visual accommodation * SC * SP * C * R #### Visual accommodation * At rest, or gazing at distant objects the lens is under tension from zonular ligament and so it is flattened * On accommodation, the ciliary muscles contract in response to parasympathetic stimulation & the tension on the zonule fibers is released * Once the tension on the lens is released it assumes more convex shape (thickened or more rounded) * This is suitable for focusing closer objects * This is accompanied by constriction of pupil #### Function of ciliary body Here is the description of the diagram of Ciliary body * Lens * Ciliary processes * Zonule fibers * the non pigmented outer layer of the ciliary processes form the aqueous humor * Cornea * Visual accommodation * Ep 1 * Ep 2 #### Formation of aqueous humor * Cells of the non-pigmented layer have tight junctions and extensive basal infoldings characteristic of ion-transporting cells, with $Na^+/K^+$-ATPase in their lateral plasma membranes * These cells actively transport fluid from the vascular stroma into the posterior chamber, thus forming the Here the description of the diagram of Aqueous Humour Pathway: * Trabecular meshwork (absorbs aqueous humour) * Canal of Schlemm (collects aqueous humour from trabecular meshwork * Sclaera * Anterior chamber * Diator/radial m *Sphincter, Cornea Conjunctiva Sclera Lens Aqueous humoris secreted into the posterior chamber flows toward the lens. The tight junction between non pigmented cells of the ciliary processes forms blood aqueous barrier that limits free movement of molecules between the ciliary body stroma & the posterior chamber ,