1.Hasan A. Mokbel Medicals International Contact lens Department The Anatomy of the Eye

2. The Eye Accessory structures Eyeball Structures Interior of the eye ball structures 3. 1. Accessory Structures Eye lids Eye Lash Eye brows Lacrimal apparatus Conjunctiva Tear film Extra ocular muscles 4. Eye Lids Its a movable thin skin folds covering the eyes Plays a role in the protection of the eye from injury by rapid closure. The eye lids include the tarsal glands that secretes oily material for lubrication and prevents evaporation of tears and stabilize the tear film. 5. Eye Lash & Eye brows The eye lashes and eye brows provide extra protection for the eye by preventing the entrance of microbial agents and dust and other matter that can cause harm to the eye. 6. Lacrimal Apparatus 7. Lacrimal Apparatus The Lacrimal apparatus is made up of many structures that is involved in nutrition , protection against pathogens and hydration roles. The Lacrimal gland is located superior to the eye lids and is an exocrine gland ( secretes in a duct ). 8. Lacrimal Apparatus The Lacrimal ducts dump the tears on the surface of the conjunctiva coming from the Lacrimal gland directly and they range from 6 to 12 duct. The Lacrimal puncta are 2 opening that collects the tears from conjunctiva and drains them to Lacrimal canal. The Lacrimal canal starts at the Lacrimal punctum and ends at the Lacrimal sac , it delivers the tears to the Lacrimal sac. 9. Lacrimal Apparatus The nasolacrimal duct descends from the Lacrimal sac to open at the meatus in the nose. 10. The Conjunctiva The Conjunctiva is a transparent mucosal layer that extends from the corneal junction to the inner portion of the eye. The Conjunctiva is divided into 2 parts : Bulbar & Palpebral. The Bulbar conjunctiva is thin , slightly vascular and surrounds the eye ball. The Palpebral is dense , highly vascular and located in the inner layer of the lid . 11. The Tear film The tear film have 3 layers : Lipid layer : is the outermost layer and is produced by Meibomian gland forms a hydrophobic barrier to trap water and prevent its evaporation. Aqueous (watery) layer : is the layer between lipid and mucous layer and contains water and proteins which has bactericidal activity also the aqueous layer regulates the osmotic pressure . 12. The Tear film The mucus layer : is produced by goblet cells found in the conjunctiva and provide a hydrophilic layer to ensure the even distribution of tears along the tear film. 13. Extra Ocular Muscles The extra ocular muscles spread along the eye ball and maintains the flexible movement of the eye . There are 7 muscles : i. The palpebral superior muscle : thin muscle that lifts the upper lid. ii. The four recti ( superior , inferior , medialis and lateralis) : the superior rectus enables the upward movement , the inferior downwards , the medialis inward and finally the lateralis outwards movement. iii. The oblique muscles ( superior obliquus and inferior obliquus muscle ) 14. 2. Eye ball structures Eye ball Fibrous tunic Vascular tunic Nervous tunic ( Retina) 15. Fibrous tunic Is the outer covering of the eye it includes : a. The cornea b. The sclera 16. The Cornea Dome shaped , transparent and non vascularized layer. Forms the outer cover of the eye . Contains highly organized cells and collagen fibers. Should remain transparent to ensure correct refraction of light. Serves as a shield against bacteria , dust and harmful materials. Gets its nourishment from the aqueous humor surrounding it. 17. The cornea The cornea is composed of 5 layers 1) The epithelial layer 2) The bowmans membrane 3) Stroma 4) Descemets membrane 5) Endothelium 18. The cornea The epithelial layer : is the outermost layer of the cornea it includes 5 to 7 layers of epithelial cells : 1. Squamous cells layer : is covered by microvilli that absorbs the tears and keep the epithelial cells hydrated. 2. The wing cell layer : composed of wing cells that is attached to each other via desmosomes which provide them with communicating abilities. 3. The basal cell layer : basal cells play a role in renewing the layer by multiplication and providing new wing cells that migrate to change to new squamous cells which replace the old squamous layer cells . 19. The cornea 20. The cornea The epithelial cells layer provide barrier to dust and infectious agents and prevents the electrolytes from tears to reach the stroma. The epithelial cells provide also a soft surface that is permeable to oxygen and nutrients via lacrimation. 21. The cornea Bowmans Membrane : contains collagen fibers and once injured regeneration is impossible. Stroma layer : Thickest layer of the cornea . Contains : 78 % water , 16 % collagen and keratocytes. It has a unique arrangement of collagen fibers in which they maintain the transparency of the cornea. The space between collagen fibers and keratocytes is filled with ground substance made up of keratin sulfate and chondroitin sulfate. 22. The cornea The Descemets membrane has 2 different layers in which the side facing the stroma have collagen fibers and the side facing the endothelium have endothelial cells . Descemets membrane have the ability to regenerate after injury. Descemets membrane provide shield against injury and infection 23. The cornea : The Endothelial layer is the innermost layer of the cornea. The Endothelial layer pumps from the stroma the any excess fluid and prevents its swelling therefore it has a role in maintenance of a clear and transparent cornea. The Endothelium lacks the ability to regenerate after injury. 24. The cornea The main function of the cornea is to refract light and direct it towards the lens . The lens accommodates and refocus the light on the retina . The retina transfers the image to nervous impulse that is transmitted to the brain via the optic nerve The brain analyses the image . The cornea also eliminates the UV light rays from the sun which is harmful for the human eye. 25. The sclera The sclera is the outer covering of the eye except for the area of the cornea. It provide protection and shape to the eye. Its superior to the choroid and posteriorly is pierced to the optic nerve The sclera is composed of : Elastic fibers Collagen fibers Fibroblasts Blood vessels 26. Vascular tunic ( uvea ) Is the middle layer of the eye and is composed of 3 constituents : o The choroid o The ciliary body o Iris 27. The Choroid Is located inferior to the sclera and superior to the retina. Dark brown tissue. Highly vascularized. It provides the retina with nutrients and oxygen. The choroid prevents the scattered light from reaching the retina. 28. The Ciliary Body The ciliary body is divided into 2 parts : The Ciliary processes : which have secretary function . The ciliary muscles : which have mechanical function. 29. The Ciliary Body The ciliary processes is responsible to secrete the aqueous humor to the anterior cavity to supply the lens and cornea with nutrients since they are not vascularized. Aqueous humor contains glucose and amino acids and respiratory gases. 30. The Ciliary Body Ciliary muscles are responsible for the accommodation of the lens by contraction and relaxation which changes the shape of the lens to flat or sphere depending on the distance of the object. 31. Iris The iris is located between the lens and the cornea . The iris divides the eye ball into anterior and posterior chambers. The iris have 2 muscles : Sphincter muscles : contracts in high light exposure and the pupil reduces its diameter allowing less light to pass. Dilator muscles : contracts at low light exposure and the pupil will dilate its diameter allowing more light to pass. 32. Nervous tunic ( Retina ) The Retina is located below the choroid . Is where the image is formed and transferred to brain via optic nerve. Composed of 10 layers : 1. Retinal Pigment epithelium. 2. The lamina of cones & rods. 3. External limiting lamina 4. Outer nuclear layer 5. Outer plexiform layer 6. Inner nuclear layer 7. Inner plexiform layer 8. Ganglion layer 9. Lamina of nerve fibers 10. The internal limiting lamina 33. Retina Retinal pigment layer : Contains melanin containing epithelial cells between choroid and neural portion. Its involved in the renewal of rod and cones photoreceptor cells by phagocyting the old aging cells. Also the retinal pigment layer absorbs light and prevents the reflection and scattering of light. 34. The neural portion It includes all the 9 layers above the retinal pigment layer. Its responsible for the early analysis of visual information before sending to the brain. The neurons are classified through which light passes through: 1. The ganglion cell layer 2. The bipolar cell layer 3. Photoreceptor layer 35. The neural portion 36. The neural portion The ganglion layer : is the final common pathway that the nerve impulse crosses since their dendrites reach the bipolar cells and the axons extends to the CNS. The bipolar cell layer : each cell with one or more dendrites extending to the cones or rods and horizontal cells and interplexiform cells , they have short axons and they are 2 types : Cone bipolar cells communicate with cone cells. Rod bipolar cells communicate with rod cells . 37. The neural portion Photoreceptor layer : ( the layer of cones and rods ) it transduces the light to the receptor due to the presence of : 120x10^6 rod neuron 6x10^6 cone neuron both cones and rods have outer segment and inner segment together they form a cone or a rod process . The inner segment decides if the photoreceptor is a cone or a Rod. 38. The neural portion The rods are responsible for the black and white vision and they are more than cones and they are concentrated at the peripheral retina and decreases in number as you reach the fovea. The cones are responsible for the colored vision and they are less in number than rods and they are concentrated(25 000) at the fovea in the macula which is a depression where the retina is extremely thin making the choroid beneath visible. 39. The neural portion These photo pigment are made up of glycoprotein called opsin and a chromatophore forming the cis-retinal a derivative of vitamin A. Retinal undergoes structural change when exposed to light and this change initiates a nervous impulse across the nerves. 40. The neural portion Retinal photo pigment is found in 2 isomer forms : Cis-Retinal (inactive form ) Trans-Retinal ( active form ) At day time Cis-Retinal gets exposed to light it gets activated and releases opsin and undergoes a structural change to trans-retinal form which causes the inhibition of glutamate neurotransmitter release and causes the closure of sodium channels which causes a hyper polarization and initiation of a nervous impulse along the nerves. 41. The neural portion The trans-retinal form causes the activation of an enzyme transducin enzyme. Transducin enzyme will activate another enzyme called Phosphodieseterase (PDE) causing the closure of Na channels. Na ions decrease inside the cell and by that the charge intracellular will decrease until it unleashes an action potential . At night time when the light is too low to activate the rhodopsin and release a nerve impulse , glutamate neurotransmitter is highly secreted which transports the impulse. 42. The Interior eye ball The Eye ball is divided by the lens into 2 parts : The anterior cavity . The posterior cavity ( the vitreous cavity). 43. Eye ball The Anterior cavity includes 2 sections : Anterior chamber ( between cornea and iris ) Posterior chamber ( between iris and the lens ) Anterior cavity is filled with aqueous humor. The aqueous humor is rich in glucose nutrients and respiratory gases its used to enrichment of the unvascularized organs. The vitreous chamber is filled with vitreous humour which is colorless gel like constancy due to the presence of collagen fibers. Vitreous humour also keeps the retina in place by pushing it against the choroid. 44. The lens The eye lens is located between vitreous humour and the iris The eye lens is 9 to 10 mm in diameter. Attached to the ciliary body via thin filaments called zonula fibers. The lens is made up of 3 parts : o Nucleus o Capsule o Cortex The lens is unvascularized and transparent The lens fibers are rich with : Crystalline ( gives the elasticity and retractile properties ). Actin ( maintain the shape of the lens. 45. The End