Lecture 1 Eye1 BMS302 Galala University Fall 2024 PDF

BMS302 Lecture 1 Eye1 Prof. dr. Manal Shaaban Faculty of Medicine, Fall 2024 Galala University gu.edu.eg  G A L A L A U N I V E R S I T Y T H E F U T U R E S T A R T S H E R E...

BMS302 Lecture 1 Eye1 Prof. dr. Manal Shaaban Faculty of Medicine, Fall 2024 Galala University gu.edu.eg  G A L A L A U N I V E R S I T Y T H E F U T U R E S T A R T S H E R E BMS 302 T H E F U T U R E S T A R T S H E R E 1.List the three coats of the eye. 2.Determine the eye chambers. 3.Describe the structure and correlated function of the cornea. 4.Describe the structure and correlated function of the sclera. 5.Determine the structural changes at corneoscleral junction and its importance 3 4 The eyes are highly developed photosensitive organ located within the hollow bony orbit. The eye is composed of 3 concentric layers: 1-Outer fibrous supporting layer: A-Cornea anterior transparent 1/6. B-Sclera posterior dense opaque 5/6. 2-Middle vascular layer (uveal layer) : A-Choroid B-Ciliary body C- Iris. 3-Inner sensory layer: A. Outer retinal pigment epithelium B. Inner neural retina 5 6 1- The anterior chamber: (filled with aqueous humour) Lies between the cornea and anterior surface of the iris. 2-The posterior chamber: (filled with aqueous humour) Lies between the posterior surface of the iris and lens. The lens is a transparent biconvex structure attach to the ciliary body by zonular fibers. 3-The vitreous chamber : ( occupied with vitreous body) Lies behind the lens and is surrounded by the retina. The vitreous body is a large gelatinous mass of transparent connective tissue The vitreous body is almost 99% water with soluble proteins, hyaluronan, glycoproteins, widely dispersed collagen fibrils It acts as a “shock absorber” that protects the fragile retina during rapid eye movement 7 , helps maintain the position of the lens and to maintain the shape of the eye.  Anterior 1/6 of the fibrous coat. Transparent and avascular. Highly innervated. It is thin in the center (0.5 mm ). It is thick in the periphery (1 mm). It is formed of 5 layers: (3 cellular layers and 2 non cellular layers). ✓ 1-Corneal epithelium. ❑ 2-Bowman’s membrane. ✓ 3-Substantia propria (stroma). ❑ 4-Descemet’s membrane. ✓ 5-Descemet’s endothelium. 10  Bowman’s membrane Descemet’s membrane 11 1- Corneal epithelium: ▪ It is a stratified squamous non keratinized epithelium, the epithelial cells adhere together by desmosomes. ▪ 5-6 layers thick resting on a straight (no ridges) basement membrane. (The basement membrane is very thick (8–12 um). ✓ The superficial flat cells:- Have microvilli to retain a film of tears between them —> to keep the cornea wet. ✓ The intermediate layers: 3-4 polygonal cells with numerous free nerve endings (The richest sensory nerve supplies of any tissue). ✓ The basal layer: single cubical cells has an excellent regenerative power by mitosis. This layer emerge from stem cells in the corneo-scleral limbus that encircles the cornea. ✓ The mitotic activity are present especially near the periphery of the cornea. ✓ Turnover of corneal epithelium = 7 days. 2- Bowman's membrane:(anterior basement membrane) Thick homogenous non-cellular layer. (It is the basement membrane of the stratified epithelium) It homogeneous, faintly fibrillar lamina formed of collagen fibrils It is synthesized by corneal epithelium & stromal cells. It acts as protective barrier against mechanical injuries & bacterial invasion. It does not regenerate, but it heals by fibrous tissue causing corneal opacities. It ends abruptly at the corneoscleral limbus. 2-Bowman’s membrane: 1-Stability & strength 2-Protective barrier Functions against trauma & bacteria. 3- Stroma (substantia propria): ✓ Thickest layer (90%). ✓ It is non vascular. ✓ Regular lamellae about 60 layers of parallel collagen fibrils. fibroblast ✓ The collagen fibrils in each lamella are arranged at right angles to the adjacent lamella. ✓ Fibroblasts are flat and are arranged in rows between the Lamella collagen lamellae called corneal corpuscles or keratocytes. ✓ Fibers & cells are immersed in ground substance ✓ Corneal proteoglycans. They maintain the organization and spacing of the collagen Lamella lamellae. The collagen lamella are arranged at right angles to the adjacent lamella  3- Substantia propria (stroma): Forms 90% of the thickness of the cornea. It consists of: Corneal corpuscles Ground substance Corneal Ground substance. collagen lamellae. (type 1 ) 60 corpuscles (Corneal Regular ( corneal fibroblasts) proteoglycans) collagen lamellae 4-Descemet’s membrane:(Posterior basement membrane) ▪ It is homogenous, thick basal lamina of corneal endothelial cells. ▪ It is formed of collagen fibers network. ▪ It is continuously synthesized by the underlying endothelium. ▪ It is readily regenerates after injury. 5-Descemet’s endothelium: ▪It is simple squamous cells lining the inner surface of the cornea. ▪It is active in protein synthesis. Why…….? to maintain the underlying basement membrane. ▪It is responsible for pumping Na+ and drawing water out of the cornea. Why.............? to maintain proper state of hydration within the cornea and to provide maximum transparency and optimal light refraction. ▪So it contains pinocytotic vesicles. ▪So it provides metabolic exchange between the cornea and aqueous humor. ▪So damage to the endothelium causing corneal swelling. 19 20 The cornea is avascular, So, How does it receive its nutrition ? From the aqueous humour (for its center). From the vessels in the limbus (for its periphery). And it receives oxygen from the atmosphere. 21  The cornea is transparent structure. Why…….? Because:- 1. It lacks of both a vascular supply and lymphatic drainage. 2. Regular arrangement of its components. 3. Same refractive indices of its components. 4.Continuous withdrawal of fluids from its stroma by …………….. 22  Does corneal transplantation from one person to another meet with success? 23  Medical applications 1- Corneal transplantation. 2- LASIK surgery: Changing the curvature of the cornea to improve certain abnormalities; myopia, hyper-metropia, and astigmatism. 3- Physical or metabolic damage to the corneal endothelium Rapid corneal swelling If the damage is severe Corneal opacity  It is the opaque, white, posterior 5/6 of the fibrous coat. It is composed of collagen bundles pass in various directions and in planes parallel to its surface. In between collagen , fine network of elastic fibers and scattered fibroblasts. The sclera about 0.5 mm in thickness (thin) anteriorly and thickened posteriorly to 1 mm. It is vascular. Its inner most layer of sclera contains Melanocytes , macrophages and connective tissue cells.  ❖The anterior exposed portion of the sclera is covered by bulbar conjunctiva. ❖The sclera gives attachment to the extra-ocular muscle to permit the rotatory movement of the eye. ❖Posteriorly, it is perforated by the optic nerve and thickened to join the connective tissue covering the nerve. 28 The sclera is composed of: Sclera proper (substantia propria): Dense connective tissue, containing thick collagen bundles , elastic fibers and fibroblasts. ✓ It is the site for insertion of extra-ocular muscle Suprachoroid layer: Inner most layer contains Melanocytes , fibroblasts (more cellular) and less collagen fibers. The sclera is opaque, Why ? Because: High content of water. Irregular arrangement of fibers. Different refractive indices of its components.  Fibrous Tunic Structure Function (External Layer) -Dense irregular connective -Supports eye shape. tissue. -Protects delicate - Relatively vascular. internal structures. Sclera - Contains melanocytes in -Attachment of its inner layer. extrinsic eye muscle. - Partially covered by conjunctiva. Cornea Two layers of epithelium -Protects anterior with organized connective surface of the eye. tissue in between. -Refracts light. ❑It is a transition zone between the cornea & the sclera {Encircle the cornea}. ❑The transparent corneal stroma merges with the opaque sclera. ❑ Limbus is highly vascularized together with aqueous humor in the anterior chamber, provides metabolites for the corneal cells by diffusion.  Corneoscleral junction Bulbar conjunctiva 34  The importance of limbus ❑ 1.The basal layer of epithelium at the limbus contains stem cells, from which rapidly dividing cells move into the cornea to generate and maintain corneal epithelium. ❑2.The presence of the stem cells at the limbus creates a conjuctival barrier to prevent migration of conjunctival epithelium into the cornea. ❑3.It contains trabecular meshwork & canal of Schlemm for drainage of the aqueous humor to aqueous vein and to small veins of the sclera. 35 Trabecular meshwork & canal of Schlemm for drainage of aqueous The aqueous humor is pumped from trabecular meshwork into the adjacent larger space called canal of Schlemm , into the aqueous and episcleral veins of the sclera. It shows the following histological characters: 1.Corneal epithelium:- is thickened from 5 to 10-12 layers and continuous with the bulbar conjunctiva (epithelium+ connective tissue.). 2.Bowman’s membrane:- Ends abruptly and replaced by sub-conjunctival connective tissue. 3. Sustantia Propria (stoma):- Become sclera with less organized oblique collagen bundles with presence of vascular stroma. -It contains a circular canal of Schlemm surrounds the limbus. 38  Corneoscleral junction Cornea Bulbar conjunctiva Iridocorneal angle Sclera Iris Ciliary body Ciliary processes zonule Lens 39 4.Descemet’s Membrane:-splits to form trabecular meshwork. 5.Descemet’s Endothelium:- Lines trabecular meshwork & canal of Schlemm. ✓ The canal of Schlemm & the trabecular meshwork lie in the iridocorneal angle.  What is the histological changes at the corneoscleral junction (limbus) and its importance? 41 Changes at corneoscleral limbus:- Corneal epithelium……. Bowman’s membrane……. Substantia propria (stroma)……….. Descemet’s membrane……. Descemet’s endothelium….. 42  THE CONJUNCTIVA It is a thin, transparent mucosa:- 1-It covers the exposed, anterior portion of the sclera. (Bulbar conjunctiva). 2-It lines the internal surface of the eyelids. (Palpebral conjunctiva).  THE CONJUNCTIVA Structure: 1-Epithelium:Stratified columnar epithelium with goblet cells 2- Lamina propria: Loose connective tissue with lymphocytes and macrophages. Conjunctivitis.  THE CONJUNCTIVA Functions: 1-Lubrication and protection (by secreting mucous). 2-Defense: it has an immunological role by its lymphocytic infiltration. 3-Drainage of aqueous humor by sub-conjunctival veins.