EYE ANATOMY Structure of the Eyeball Sclera and Cornea The eyeball can be divided into two main parts the sclera and the cornea Sclera The sclera is the outermost layer of the eyeball and provides structural support and protection It is a tough white fibrous layer that is continuous with the cornea in the front and the connective tissue around the eye Tunics of the Eyeball The eyeball can be divided into three main tunics Fibrous Tunic composed of the cornea and sclera Cornea transparent front part of the fibrous tunic provides two thirds of the total refractive power of the eye Sclera tough white outer covering of the eye that provides protection and shape Vascular Tunic composed of the choroid ciliary body and iris Choroid highly vascular layer that contains blood vessels which supply the retina Ciliary Body consists of the ciliary muscle and ciliary processes responsible for accommodation reflex Ciliary Muscle controls the shape of the lens by contracting or relaxing Iris pigmented circular structure that controls the amount of light that enters the eye by adjusting the size of the pupil Dilator Pupil smooth muscle of the iris that dilates the pupil Sphincter Pupil smooth muscle of the iris that constricts the pupil Sensory Tunic composed of the retina and optic nerve Retina innermost layer of the eyeball contains photoreceptor cells rods and cones and is the site of the phototransduction process Optic Nerve transports visual information from the retina to the brain Optic Disc point where the retina and the optic nerve meet does not contain photoreceptor cells Vitreous Humor The vitreous humor is a gel like substance that fills the space between the lens and the retina It provides structural support and helps maintain the shape of the eyeball Structure of the Eyeball Sclera and Cornea Sclera white outer layer of the eye that provides protection and shape Cornea transparent front part of the fibrous tunic provides two thirds of the total refractive power of the eye Layers of the Cornea The cornea consists of five distinct layers Epithelial outermost layer provides a smooth surface that aids in refraction Bowman s Membrane strong acellular membrane that protects the corneal stroma Stroma main layer of the cornea provides structural support Descemet s Membrane strong thin layer that separates the stroma and endothelium Endothelial innermost layer of the cornea responsible for maintaining corneal hydration Canal of Schlemm The canal of Schlemm is responsible for drainage of aqueous humor from the anterior chamber of the eye reducing intraocular pressure Tears and Lacrimal System The lacrimal system is responsible for producing distributing and draining tears This system includes Lacrimal gland located in the upper outer part of the orbit produces tears Lacrimal ducts carries tears from the lacrimal gland to the eye Puncta openings in the inner corner of the eyelids that drain tears into the lacrimal ducts Lacrimal sac located in the bony structure at the inner corner of the eye collects tears from the lacrimal ducts Nasolacrimal duct drains tears from the lacrimal sac in to the nasal cavity Eye Muscles and Their Functions There are six extraocular muscles responsible for eye movements Lateral Rectus abducts the eye Medial Rectus adducts the eye Superior Rectus elevates and intorts the eye Inferior Rectus depresses and extorts the eye Superior Oblique depresses intorts and abducts the eye Inferior Oblique elevates extorts and abducts the eye ayers of the Cornea The cornea is a transparent avascular structure that forms the anterior part of the eyeball It consists of several layers each with its unique structure and function Epithelial Layer The outermost layer of the cornea Composed of stratified squamous epithelial cells Provides a barrier against the external environment protecting the eye from bacteria viruses and other harmful substances High proliferation rate allowing for quick repair of damages Bowman s Membrane Thin acellular layer located beneath the epithelial layer Composed of randomly arranged collagen fibrils Serves as a protective barrier against injury to the underlying Unlike other corneal layers it has no capacity for repair or stroma regeneration Stroma The thickest layer of the cornea Comprised of regularly arranged collagen fibrils interspersed with keratocytes Provides structural support and transparency to the cornea Descemet s Membrane endothelium pattern Endothelial Layer Thin acellular layer located between the stroma and Composed of collagen fibrils arranged in a delicate lamellar Maintains the curvature and stability of the cornea The innermost layer of the cornea Composed of a monolayer of hexagonal cells Regulates the hydration state of the cornea by actively pumping water out of the stroma Unlike other layers of the cornea the endothelium does not regenerate and can only be restored through a corneal transplant Canal of Schlemm The canal of Schlemm is a circular vein like structure located in the limbus the region between the cornea and sclera It plays a critical role in the eye s drainage system responsible for the flow of aqueous humor from the anterior chamber to the venous system The aqueous humor is a clear fluid that provides nutrients and removes waste from the avascular structures in the eye such as the lens and the cornea The flow of aqueous humor creates intraocular pressure ensuring the proper shape and function of the eye When the pressure within the eye is too high or too low several eye related diseases can occur such as glaucoma Generate Multiple Choice QuizSearch The Web for similar contentGenerate FAQsRegenerate this Summary Parts of the Iris The iris is a circular thin diaphragm that divides the anterior chamber of the eye into two sections It is responsible for controlling the amount of light that enters the eye by adjusting the size of the pupil The iris contains two muscles 1 Dilator Pupil This muscle is responsible for enlarging the pupil It is a smooth radial muscle that is innervated by sympathetic nerves 2 Sphincter Pupil This muscle is responsible for constricting the pupil It is a circular muscle that is innervated by parasympathetic nerves Structure of the Eyeball Sclera and Cornea The eyeball is composed of three layers or tunics fibrous vascular and sensory The outermost layer is the fibrous tunic which includes the sclera and cornea 1 Sclera This is the tough white outer coat of the eyeball that provides protection and