ANATOMY OF VISION: THE VISUAL PATHWAYS BY Ph.D. Alsayed Ali Mahran MAHRAN S.A 2- Sight (vision) Sight or vision is the ability to see ,and it is the dominant sense in humans. 70% of sensory receptors in humans are in the eyes 40% of the cerebral cortex is involved in processing visual information The eye (or eyeball) is the visual organ • Diameter 2.5 cm (1 inch) • Only anterior 1/6 visible • Lies in bony orbit • Surrounded by a protective cushion of fat MAHRAN S.A Anatomy of the eye • The eye (or eyeball) is the visual organ • Diameter 2.5 cm (1 inch) • Only anterior 1/6 visible • Lies in bony cavity in the front of skull called orbit • Surrounded by a protective layer of fat called periorobital fat. Anterior view of skull showing MAHRAN S.A orbits containing eyes Anatomy of the eye includes Accessory Eye ball and its structures of the layers; eye: 1.Outer fibrous layer 1.Eyebrows (cornea &sclera). 2.Eyelids or palpebrae Upper & lower 2.Middle vascular layer (choroid ,ciliary body 3.Lacrimal apparatus & iris). 4.Extraocular 3.Inner nervous layer (extrinsic) eye (retinal & obtic nerve). muscles MAHRAN S.A A) Accessory structures MAHRANof the S.A eye ,and B) Eye ball The eyebrows: The eyebrow is an area of thick, delicate hairs above the eye . It consists of skin, subcutaneous tissue and groups of muscles. Functions: 1-Their main function is to prevent sweat, water, and other debris from falling down into the eye. 2- It is used also in human communication and facial expression. MAHRAN S.A Anatomy of eyelids Eye lid : It is fibromuscular fold covering anterior surface of eye ball . Upper eye lid is more movable than lower eye lid as it have levator palpebrae superioris muscle and Muller's muscle . -The palpebral fissure is that empty space between the upper and lower eyelid margins when the eyelids are open . - The points at which the upper and lower eyelids fuse together at both sides of the eye are called canthi. - The edge of either eyelid (the junction where the front and back sides join together) is called the eyelid margin= 2 mm. -The eyelashes are located on the most forward edge of the lid margin. MAHRAN S.A Structural Layers of Eyelid: From anterior to posterior the eyelid consists of ; 1-Skin ; thin skin 2-Subcutaneous tissue ,not contains fat 3-muscle layer ,both striated Muscle ( Orbicularis Occuli &Levator Palpebral Superioris ) and smooth muscle ( Muller’s Muscle) 4-Tarsal Plates ;dense connective tissue that responsible for the integrity of the lids (give shape and firmness to the lids). 5-Conjunctiva; is the mucous membrane that lines the eyelid(palpebral part) and covers the visible portion of the eyeball(bulbar part) except the cornea . MAHRAN S.A Structure of the eyelidMAHRAN S.A Eyelashes: Eyelashes are thee to five rows of hair attached to the eyelids. The upper lid lashes are directed upward, and outwards The lower lid lashed are directed downward and outwards MAHRAN S.A List the glands related to the eyelid: The glands related to the eyelid are: Meibomian gland; is modified sebaceous gland lies within the tarsal plate and open at the lid margin behind the eyelashes. It secrete an oily material to tear film to prevent its rapid evaporation. Gland of Zeis; is a sebaceous gland open on stem of eyelashes. Gland of Moller's; is modified sweat gland open on the lid margin. MAHRAN S.A Lid retractors: The lid retractors are responsible for opening the eyelids. the upper lid are levator palpebrae superioris (innervated by the oculomotor nerve=3rd CN) & Muller's muscles (smooth muscle innervated by sympathetic nerves) the lower lid is the inferior rectus muscle ((innervated by the occulomotor nerve=3rd CN) MAHRAN S.A What are the functions of eyelid and eyelashes? Eyelids and Eyelashes. protect the eye from foreign objects, such as dust, dirt, and other debris, as well as bright light e.g., sun light that might damage the eye. the eyelids also help spread the tears over the surface of the eye, keeping the eye moist and comfortable. This occurs by blinking, which normally occurs about 25 times per minute. MAHRAN S.A N.B Movements of the eyelids are a function of skeletal muscles. the levator palpebrae The orbicularis oculi superioris elevates the upper Muscle closes the lids (close the lid (open the eye). It eye).It innervated by the facial innervated by the th nerve (5 CN). oculomoter nerve (3rd CN). *So we open the eye by *So we close the eye by the the facial nerve MAHRAN S.A oculomoter nerve Lacrimal Apparatus: Lacrimal Apparatus is responsible for production and drainage of tear. It consists of:- Lacrimal Gland, which formed of a large orbital part .and a small palpebral part .It lies in the anterior and upper part of the orbit . Lacrimal gland secretes the Tears which flow down the front of the eye and drain by, Two lacrimal canaliculi ,then to, The lacrimal sac and finally by , Nasolacrimal duct which open in the inferior nasal meatus. MAHRAN S.A Lacrimal apparatusMAHRAN S.A The extraocular muscles of the eye The extraocular muscles of the eye are the six (4 recti + 2 oblique) which act to move the eye about its vertical, horizontal, and antero-posterior axes: superior rectus (SR), moves the eye upward (elevation) inferior rectus (IR), moves the eye downward (depression) medial rectus (MR), moves the eye inward, toward the nose (adduction) MAHRAN S.A Extraocular muscles of the eye MAHRAN S.A lateral rectus (LR), moves the eye outward, away from the nose (abduction) superior oblique (SO), moves the eye downward (depression) and laterally. Inferior oblique (IO). moves the eye upward (elevation) and medially Nerve supply of extraocular muscles: All the extraocular muscles are supply by the oculomotor nerve (3rd cranial nerve) except; 1. Lateral rectus which supplied by abducent nerve(6th cranial nrerve) and 1. Superior oblique which supplied by trochlear nerve (4th cranial nerve). MAHRAN S.A Names, actions, and cranial nerves innervated of the extrinsic eye muscles. MAHRAN S.A The Eyeball: The eyeball is globe-shaped occupies the anterior part of the orbit (bony cavity in front of skull) The eyeball is divided into two chambers, The anterior chamber lies between the cornea and the iris, and filled by a watery solution called the aqueous humor. the posterior chamber lies between the lensand retina and filled by a gel-suspension called the Vitreous humor. MAHRAN S.A Nerve supply of extraocular muscles MAHRAN S.A Lens: It is a transparent, biconvex elastic disclies behind the iris . Walls of the eyeball: • The eyeball consists of three layers of fibrous tissue, which are covered by a fine transparent membrane called the conjunctiva.; 1) the outer fibrous layer consists of the cornea anteriorly and the sclera posteriorly; The Cornea, is a thin transparent covering the front part of the eye. It has no blood vessels, it responsible for the refraction of the light entering the eye. MAHRAN S.A Horizontal sectionMAHRAN of S.A right eye The Sclera, is the non-transparent (white of the eye) , and is continuous with the clear cornea anteriorly. 2) the middle vascular layer consists of; The choroid; is a thin tissue layer containing blood vessels sheet of blood vessels, iies between the sclera and the retina. It carries oxygen and nutrients to the eye and removes carbon dioxide and wastes. It also prevents light in the eye from scattering. MAHRAN S.A The iris is the colored part of the eye with a central aperture,called the pupil ,It Projecting from the ciliary body and its primary function is to control the amount of light hitting the retina,as it contract in bright light or expand in dim light . MAHRAN S.A MAHRAN S.A The retina is the sensory portion of the eye and contains Visual Receptors which are:- -Cones -Rods provide vision in bright provide vision in dim light light produce color vision produce colorless produce sharp images vision produce outlines of objects The macula is small central area of the retina that provides vision for fine work and reading the fovea, is a small depression (approx. 1.5 mm in diameter) in the retina, involved with high-resolution vision of fine detail MAHRAN S.A The retina is the sensory portion of the eye and contains Visual Receptors which are:- -Cones -Rods provide vision in bright provide vision in dim light light produce color vision produce colorless produce sharp images vision produce outlines of objects -The macula is small central area of the retina that provides vision for fine work and reading -The fovea, is a small depression (approx. 1.5 mm in diameter) in the retina, involved with high-resolution vision of fine detail -The optic disc is the site where the optic nerve leaves the eye and the central retinal artery enters the eye. It is completely devoid of rods and cones so that it is insensitive to light and is referred to as the blind spot . MAHRAN S.A Ophthalmoscopic viewMAHRAN of posterior S.A chamber of the eye. Focusing On Retina • as light enters eye, it is refracted by • convex surface of cornea • convex surface of lens • image focused on retina is upside down and reversed from left to right MAHRAN S.A Visual Nerve Pathway MAHRAN S.A THANK YOU ANY QUESTION MAHRAN S.A.