Physiology of Vision

PHYSIOLOGY OF VISION 12 The eyes are the visual oregans the eyes organd. which make one of the most complex of the sense The eyes arme called photo receptom Interenal Structure of Eye ball: → The eye ball is a globular structure Part of it is visible from outside. and only Ysth The Ls of the Structure. eye ball consists of tellowing a) outer fibrous coat the sclera b) Middle Vascular coat the choroid Inner herrvous coat the reetina a) Sclerca: The sclera is formed of opaque fibrous Connective Hosue and surrounds the entire eyeball. At the anterior exposed portion a part of the Coat be comes transparent to form the Conneg which remain coverned by conjuctiva. b) Choreoid: It is a soft, thin. Layer formed of numerious capillaries and provide nutrition. choroid is subdivided into choroid propers, fris and ciltary body ⅰ) choroid propen: at fo a dank, pigmented and highly vascular membrane, It is also modified at the front of the eyen forming pigmented iris and the ciliary body : The ini's inis: middle coat to the anterior portion It is thin, circular, muscular, usually pigmented, centrally pereforcated of the It has a central circular opening called perpil → The tris to provided diameter of the pupil. with muscles which control the → The inis reegulates accurately the entering the eyeball proper. amount of light ⅲ) Cilfany body: just behind the inis the ciliary body is present →ot bears the elliary processes which gives attachment to the fibres of the ligament of the lens sugen sory wh Retina: It is the Innenmost coat on layer of the eye ball which contains light receptors! It is the moet sensitive pant of the eye. The entire inner surface of the eye ball is lined by retina except for the anterior protion Where it ends near the lens. The anea of the retina where ofthe nerve enters Slightly eleveted called blind spot where the photorecepton cells are abpent. Above the blind spot immediately opposite to the Optical axis of the lens. is the yellow spot in the centre of yellow spot there is a depression called fovea centralis This region contain only comecells fore cleanest Vision. Microscopic structure of Retina! Retina is formed of two layers outer pigmented layen attached to the chorroid and Visual cells to an innere sensitive region formed , nen ves The visual cells on photoreceptores are of two types : rods and cones. →The rods contain chodopsin pigments. The Rods are concerned with vision in dim light. the cones contain todopsin pigment which are Concerned with bright light & colour Vision. Long, Just behind the inis there is a circulan transparent, elastic and biconvex lens which lies vertically → The lens fo held in position by Suspensong ligament attached to ciliany body lens Cambel changed by shape of the lens The s the action of the ciliary body. chambers: The cavity of the eye ball is divided into two chambers The space between inis and cornea is the anterior chamber on aqueous chamber filled with Clean Water fluid aqueous humoun. →The space between the posteriore face of the lens and tretina is the Vitreous chamber which to filled with a treans pament, j'elly like substance the Vitreous humour Working of eye: → Each eye Camera works Similar to a photographic Eye to a photoreceptor and responsible for the vision vision means the formation of extennal objects on the retina. Images of the → These images optic nerve are then conveyed through the and and interpreted by the brain. Accomodation of the eye: → Animals arce able to see both distant and nearby objects by changing the curvature of the lens and hence the focal length of the lens. This adjustment is known as accomodation. →this accomodation is effected by the changes In the convexity of the lens. control of light: The amount of light necessary for vision Should be regulated" the the size of the pupil. • This is done by adjusting bright light the pupil becomes Small, allowing requiried amount of light ⇒on dim light it becomes lange thus allowing maximum light. This is intimately associated" with the accommodation mechanism. Formation of image on the retina: →for the formation of image on the retina the basic requinement is that light exteanal objects on the retina. Should be brought to a forus →This is possible by the nefractive system of the eye through accomodation. →Firest of all the light rays entening the eye, reflected from an object, is refracted by the come a and aqueous humour. Then it is focussed by the biconvex lens. The shape of the lens is changed due to the action of ciliary muscles and elasticity of the lens itself. → The rays of light taom an object ane bent by the lens and pass through the Vitreous humours So that on the retina. they convenge → As the rays enter the eye, they eross one another and a shang fuvented image is formed on the retina and that too on the yellow spot. This invented image is interpreted by the brain in such a relationships way that objects are seen in their connect The perception of objecte is a of the rods and cones of the retina. result of the interaction → on other words fmage formation is due to the bleaching of the chodopsin and iodopsin found in the nod and cones reespectively The reads perceive black, white while the cone Penceive the othen colours. A night when colours are gradually lost the cones cease to function and vision to mainly dice to rods. →cones function in highen intensity of light and rods in the lowen intensity of light