6.1 Sense of Vision PDF - Anatomy and Physiology 2

 RNB10702 ANATOMY AND PHYSIOLOGY 2 SENSE OF VISION  LEARNING OUTCOMES At the end of the session, the students should be able to: describe the accessory structure of the eye and their functions describe the anatomy of the eye describe the anatomy of eye cavities and their...

 RNB10702 ANATOMY AND PHYSIOLOGY 2 SENSE OF VISION  LEARNING OUTCOMES At the end of the session, the students should be able to: describe the accessory structure of the eye and their functions describe the anatomy of the eye describe the anatomy of eye cavities and their chambers discus the refraction of light and image formation describe the stimulation of photoreceptors discus the visual pathway to the brain  INTRODUCTION More than half the sensory receptors in the human body are located in the eyes A large part of the cerebral cortex is devoted to processing visual information The eye is the organ of the sense of sight situated in the orbital cavity and it is supplied by the optic nerve (2nd cranial nerve)  ACCESSORY ORGANS OF THE EYES Eyebrows/eyelashes Eyelids Conjunctiva Lacrimal apparatus Extraocular muscles EYELASHES AND EYEBROW Eyelashes - protect the eyeballs from foreign objects, sweat and direct rays of the sun Eyebrows - divert sweat from the eyes and contribute to facial expressions  EYELID Function  Protect the eyes from excessive light  Protect from injury  Help to keep the cornea moist Orbicularis muscle – closes the lids Levator palpebrae superioris muscle – raises upper eyelids  CONJUNCTIVA The conjunctiva is a thin mucous membrane that lines the inner aspect of the eyelids and is reflected onto the anterior surface of the eyeball CONJUNCTIVA (CLINICAL APPLICATION) Conjunctivitis - inflammation of the conjunctival sac  LACRIMAL APPARATUS It is a group of structure that produce & drain away tears–located in the upper outer conner of each orbit Consists of lacrimal gland, lacrimal canal, lacrimal sac & nasolacrimal ducts Lacrimal gland – produced tears contain salt, water & lysozyme  LACRIMAL APPARATUS (cont..) Flow of tears Tears that produce in lacrimal gland flow into the lacrimal puncta, which are two openings on the nasal side of the extreme edge of the eyeball Superior and inferior lacrimal canals empty the tears into the nasolacrimal sac and nasolacrimal duct – The right and left sided nasolacrimal ducts empty into each side of the nose  LACRIMAL APPARATUS (cont..) …Flow of tears  LACRIMAL APPARATUS (CLINICAL APPLICATION) Watery eyes - occur when there is obstruction the nasolacrimal ducts Blocked nasolacrimal ducts - caused by an inflammation of the nasal mucosa, such as a cold Over production of lacrimal fluid - occurs in response to parasympathetic stimulation due to an emotional response (crying), and tears spill over the edges of the eyelids and drain into the nasal cavity (causing nasal stuffiness)  EXTRAOCULAR MUSCLE OF THE EYE The six extrinsic muscle of the eye attached to the sclera & move the eyeballs in all directions  ANATOMY OF THE EYE The walls of eyeball consists of 3 layer of tunics Fibrous Tunic - sclera and cornea Vascular Tunic (Uvea) - choroid, ciliary body & iris Nervous Tunic – retina  ANATOMY OF THE EYE (cont..) The internal cavity is filled with fluids called humors The lens separates the internal cavity into anterior and posterior segments Anterior Segment contains the Aqueous Humor Posterior Segment contains the Vitreous Humor  FIBROUS TUNIC It is the outer coat of the eyeball Protects the intraocular contents Divided into 2 – sclera & cornea At the junction of the sclera and cornea is an opening known as the scleral venous sinus or canal of Schlemm  FIBROUS TUNIC (cont..) Sclera Known as “white” of the eye Function - maintains the shape of the eye and gives attachment to the extrinsic muscle  FIBROUS TUNIC (cont..) Cornea Continuously from sclera The cornea is convex anteriorly Acts as refracting (bending) & focus light rays on the retina LASIK is a common visual corrective procedure that is performed on the cornea of the eye  VASCULAR TUNIC It is the middle layer of the eyeball Composed of 3 portions: choroid, ciliary body, and iris  VASCULAR TUNIC (cont..) Choroid Line between the sclera & retina Contain blood vessels – nourish the retina Contain melanocytes – produce melanin cause the layer dark brown in color - absorbs light rays so that they are not reflected and scattered within the eyeball  VASCULAR TUNIC (cont..) Ciliary Body Consists of two parts: o Ciliary processes - secrete aqueous humor o Ciliary muscle -changes the shape of the lens to adapt to near and far vision  VASCULAR TUNIC (cont..) Iris Colored portion of the eyeball Pupil - black hole in the center of the iris  Function - regulate the amount of light reaching the retina  SENSORY TUNIC; RETINA Retina The innermost layer of the eyeball A thin, delicate & transparent membrane Function – receives lights & converts it into nerve impulses Divided into optic disc, macula lutea & peripheral retina  RETINA (cont..) Optic disc – blind spot of the vision & the site where the optic nerve enters the eyeball Macula lutea – area rich with cones & it is the exact center of the posterior portion of the retina The fovea centralis in the centre of macula lutea, the point of sharpest vision in the retina – due to the high concentration of cones  RETINA (cont..) Contain photoreceptors called rods and cones Rods Specialized for black-and-white vision in dim light Allow us to discriminate between different shades of dark and light Permit us to see shapes and movement Cones Specialized for color vision and sharpness of vision (high visual acuity) in bright light Most densely concentrated in the central fovea, a small depression in the center of the macula lutea. RETINA (cont..) RETINA (CLINICAL APPLICATION) Retinal detachment – retina peels away from its underlying layer of support tissue may result in visual distortions or blindness RETINA (CLINICAL APPLICATION) cont.. Diabetic retinopathy – blood vessels may become blocked or damaged & damages the retina. Common complication of diabetes and the main cause of blindness in people under 65 years old RETINA (CLINICAL APPLICATION) Age Related Macular Degeneration results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It is a major cause of visual impairment in older adults (>50 years) – It can become impossible to recognize faces, yet enough peripheral vision remains to allow other activities of daily life  INTERIOR OF THE EYEBALL Contains Anterior & posterior chamber – contain aqueous humor Lens Viterous humor ANTERIOR & POSTERIOR CHAMBER Anterior cavity Space between cornea & lens Composed 2 chambers  Anterior – between the cornea and the iris  Posterior – between the iris and the lens  ANTERIOR & POSTERIOR CHAMBER (cont..) Contain aqueous humor – secreted by ciliary glands Function of aqueous humor  Supplies oxygen, nutrients and removes waste the cornea, lens and lens capsule  Helps maintain the shape of the eye Scleral venous sinus (canal of Schlemm) returns aqueous humor to the blood stream  ANTERIOR & POSTERIOR CHAMBER (cont..) Posterior cavity (vitreous chamber) Large region lies between the lens & the retina Filled with vitreous humor Formed during embryonic life and is not replaced thereafter  ANTERIOR & POSTERIOR CHAMBER (cont..) Vitreous humor - is a soft, colourless, transparent, jelly-like substance that:  Helps maintains the shape of eyeball  Keeps the retina attached to the choroid  Transmit light The eye keeps its shape because of the intraocular pressure exerted by the vitreous body and the aqueous fluid. It remains fairly constant throughout life  AQUEOUS HUMOR(CLINICAL APPLICATION) Glaucoma – occurs when the aqueous humor does not flow out of the eye properly. An excessive intraocular pressure occurs causes damage to the eye’s optic nerve & lead to blindness if left untreated  LENS It is biconvex, avascular, colorless & transparent structure Located behind the iris pupil Its thickness is controlled by the ciliary muscle Function - focus the light rays onto the retina (refraction)  LENS (CLINICAL APPLICATION) Cataracts - the lens of the eye becomes hard and opaque which is a common complication of diabetes mellitus May also caused by smoking and exposure to the UV radiation of the sun They can be treated by replacing the natural lens with a plastic one PATHWAY OF LIGHT AND REFRACTION Normal image formation depends on: 1. Refraction of light waves 2. Accommodation of the lens 3. Constriction of the pupil 4. Convergence of the two eyes  REFRACTION It is the process of bending light rays The refractive media of the eye – cornea, aqueous humor, lens & viterous humor In normal eye, the refractive media bends the light rays from objects at least 20 feet away to focus on the retina The image form on the retina is upside down & backward but the brain will turn it around & interpret the image in the correct position  REFRACTION (cont..) 75% of total light refraction occurs at the cornea Lens further refract light rays so they come into exact focus on the retina  REFRACTION (cont..) In order to focus light that has already been bent by the cornea the lens must change shape – the amount depending on the type of light rays we are trying to “see”  ACCOMODATION It is an adjustment in the shape of the lens Normal relaxed eye is able to focus the image on the retina in at least at 20 feet away If object less the 20 feet (closed vision)  Ciliary muscle contract  Suspensory ligaments become loose or relaxed  Lens becomes bulges (thicken) or more convex The closer the object, the more light rays have to bend to focus & greater curvature of the lens  ACCOMODATION (cont..) If the object more than 20 feet (far vision)  Ciliary muscle relaxed  Suspensory ligaments become taut  Lens becomes flat  THE PUPILLARY RESPONSE The pupil is an opening in the center of the iris. It is composed of a radial muscle that “radiates” away from the center, and a circular muscle that is in the center Contraction of the inner circular muscle fibers cause the pupil to constrict while contraction of the radial fibers cause it to dilate  CONVERGENCE It is the inward movement of the eyes so that both are directed at the object being viewed - becoming a little cross-eyed when viewing things close up The nearer the object, the greater the degree of convergence needed to maintain binocular vision o the coordinated action of the extrinsic eye muscles brings about convergence Convergence helps us maintain our binocular vision and see in three dimensions REFRACTION ABNORMALITIES Myopia is nearsightedness - image is focused in front of the retina – correction with the use of a concave (negative) lens REFRACTION ABNORMALITIES (cont..) Hyperopia is farsightedness - image is focused in behind of the retina - correction with the use of a convex (positive) lens REFRACTION ABNORMALITIES (cont..) Astigmatism is a refraction abnormality due to an irregular curvature of either the cornea or lens  PHOTORECEPTORS The retina contains 2 kinds of photo receptor cells - rods and cones After an image is formed on the retina by refraction, accommodation, constriction of the pupil, and convergence, light rays must be converted into neural signals The initial steps is the absorption of light by photopigments (visual pigments) in rods and cones Photopigments - It is colored proteins that can absorb light & undergo structural changes upon light absorption  PHOTORECEPTORS (cont..) Rods It is thin cells with slender, rodlike projections Specialized for black-and-white vision in dim light It is more than cones Rhodopsin - photopigment of rods that very light sensitive Light phase - rhodopsin breaks down into opsin & retinal (bleaching the pigment) Dark phase - opsin & retinal recombine into rhodopsin  PHOTORECEPTORS (cont..) Cones Specialized for color vision and sharpness of vision (high visual acuity) in bright light There are 3 types of cones: blue, green, and red Cones are most densely concentrated in the central fovea, a small depression in the center of the macula lutea – for sharpest vision Intermediate colors are perceived by activation of more than one type of cone  PHOTORECEPTORS (CLINICAL APPLICATION) Night blindness – occur due to low amount of rhodopsin caused by prolonged vitamin A deficiency Colorblindness - An individual with an inherited absence of or deficiency in one of the three types of cone photopigments & are more in males. The most common type, red- green color blindness, either red cones or green cones are missing. Thus the person cannot distinguish between red and green  OPTIC NERVE, OPTIC CHIASMA & OPTIC TRACT Optic nerve - cranial nerve carrying impulses from the retina to the brain Optic chiasma - point at which optic nerve fibers cross in the brain (chiasm means crossing) Optic tract - this extends from the Optic chiasma to the thalamus, it is for visual awareness  VISUAL PATHWAY After stimulation by light, the rods & cones trigger electrical signals to ganglion cells Impulses from ganglion cells are conveyed through the retina to the optic nerve to the optic chiasma. From the optic chiasma, the impulse travel on the optic tract to the thalamus. From there, the impulses travel on optic radiations to the visual cortex in the occipital lobe  RECAP/QUIZ Name the clear mucous membrane that covers the white part of the eye. Conjunctiva Name the structure that secretes tears to moisten the cornea & conjunctiva. Lacrimal gland List the contains of tears. Mucus, antibodies, and lysozyme Name the 3 layers of eyeballs. Fibrous Tunic, Vascular Tunic & Nervous Tunic  RECAP/QUIZ (cont..) Name the structures in the fibrous Tunic. Sclera and cornea What are the structures in the vascular Tunic? Choroid, ciliary body & iris Name the structures in the nervous Tunic. Retina The internal cavity separates into anterior and posterior segments by…. Lens  RECAP/QUIZ (cont..) What is the shape of the lens that will focus to light waves? Biconvex What is the structure in the fibrous tunic known as “white” of the eye? Sclera What is the structure that involved in refracting & focusing light rays on the retina? Cornea The anterior cavity of the eyeball is filled by… Aqueous humor  RECAP/QUIZ (cont..) The posterior cavity of the eyeball is filled by Vitreous humor What is the characteristic of vitreous humor? Soft, colourless, transparent, jelly-like substance Aqueous humor is produced by Ciliary process Aqueous humor return to the blood stream via Scleral venous sinus What condition that occurs when the aqueous humor does not flow out of the eye properly? Glaucoma  RECAP/QUIZ (cont..) The mechanism where the lens curve for near vision is called Accommodation What is the condition occurs due to low amount of rhodopsin caused by prolonged vitamin A deficiency? Night blindness The photopigment of rods is called Rhodopsin What is the photo receptor that is sensitive to dim light and best suited for night vision? Rods