4; Parts of the Brain 4; Eye … It is a white visible position and protective outer layer of the eye & is continuous anteriorly with the transparent cornea. The cornea’s main function is refracting light rays to focus them on the retina. This is achieved by the eyelids, which during waking hours sweep the secretions of the lacrimal apparatus and other glands over the surface at regular intervals and which during sleep cover the eyes and prevent evaporation. The protrusion of the eyeballs—proptosis—in exophthalmic goitre is caused by the collection of fluid in the orbital fatty tissue. A horizontal cross section of the human eye, showing the major parts of the eye, including the protective covering of the cornea over the front of the eye. Required fields are marked *. The skin of the forehead, temple, and cheek is then drawn toward the medial (nose) side of the orbit, and the radiating furrows, formed by this action of the orbital portion, eventually lead to the so-called crow’s feet of elderly persons. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Human Eye: Anatomy, parts and structure. You may know that the human brain is composed of two halves, but what fraction of the human body is made up of blood? The palpebral portion passes across the lids from a ligament called the medial palpebral ligament and from the neighbouring bone of the orbit in a series of half ellipses that meet outside the outer corner of the eye, the lateral canthus, to form a band of fibres called the lateral palpebral raphe. Structure of the Human Eye The eye is a hollow, spherical structure about 2.5 centimeters in diameter. The retina is a complex nervous structure, being, in essence, an outgrowth of the forebrain. It is situated in the orbital cavity in the skull. Its wall has three distinct layers—an outer (fibrous) layer, a middle (vascular) layer, and an inner (nervous) layer. The human eye is a paired sense organ that reacts to light and allows vision. The human eye is a roughly spherical organ, responsible for perceiving visual stimuli. The retina is the innermost layer of the wall of the eye. The muscle of Riolan, lying close to the lid margins, contributes to keeping the lids in close apposition. Get a Britannica Premium subscription and gain access to exclusive content. The outermost layer of the lid is the skin, with features not greatly different from skin on the rest of the body, with the possible exception of large pigment cells, which, although found elsewhere, are much more numerous in the skin of the lids. The eye is the organ of sight. Structure of Human Eye: The eye is a hollow, spherical structure measuring about 2.5 cm in diameter. The eye is supplied with arterial blood by the ciliary artery and central retinal artery. Eye lens changes its shape and thickness to adjust the focus on to the retina. The eye is the organ of sight. In lid opening, the frontalis muscle, arising high on the forehead, midway between the coronal suture, a seam across the top of the skull, and the orbital margin, is attached to the skin of the eyebrows. Parasympathetic stimulation constricts the pupil and Sympathetic stimulation dilates. When the lids are closed, the whole opening of the orbit is covered by this septum. It is also brought into action when vision is rendered difficult either by distance or the absence of sufficient light. Your email address will not be published. The conjunctiva is a mucous membrane that serves to attach the eyeball to the orbit and lids but permits a considerable degree of rotation of the eyeball in the orbit. It absorbs light rays from our environment and transforms them in such a way that the information in the brain can be processed it lies in the eye socket and is attachedto various muscles. The lid may be divided into four layers: (1) the skin, containing glands that open onto the surface of the lid margin, and the eyelashes; (2) a muscular layer containing principally the orbicularis oculi muscle, responsible for lid closure; (3) a fibrous layer that gives the lid its mechanical stability, its principal portions being the tarsal plates, which border directly upon the opening between the lids, called the palpebral aperture; and (4) the innermost layer of the lid, a portion of the conjunctiva. The optic foramen, the opening through which the optic nerve runs back into the brain and the large ophthalmic artery enters the orbit, is at the nasal side of the apex; the superior orbital fissure is a larger hole through which pass large veins and nerves. 151,998,502 stock photos online. The structure of the eye is an important topic to understand as one of the important sensory organs in the human body. In addition to the muscles already described, other facial muscles often cooperate in the act of lid closure or opening. The retina of human eye has a static contrast ratio of around 100:1 (about 6.5 f-stops). The nervous connections of this muscle are closely related to those of the extraocular muscle required to elevate the eye, so that when the eye looks upward the upper eyelid tends to move up in unison. Save my name, email, and website in this browser for the next time I comment. New users enjoy 60% OFF. Size and shape: Human eye is spherical about 2.5 cm in diameter. Each gland has two portions. So while you know what parts of your brain are the most active when you see something, no one quite knows how we perceive the world as a result. Vascular layer of eyeball: The second or middle layer is the choroid layer which is thin and vascular (has blood vessels to supply blood and oxygen) made up of connective tissue. Our editors will review what you’ve submitted and determine whether to revise the article. The purpose of the retina is to receive light that the lens has focused,convert the light into neural signals ,and send these signals on to the brain for visual recognition . That is to say. The orbicularis and levator are striated muscles under voluntary control. Your email address will not be published. The iris controls the size of the pupil, which is the opening that allows light to enter the lens. The cornea is the clear window through which light can enter. The puncta are openings into the lacrimal ducts; these carry the tears into the lacrimal sacs, the dilated upper ends of the nasolacrimal ducts, which carry the tears into the nose. The other portion projects into the back part of the upper lid. As soon as the eye moves, it re-adjusts its exposure, both chemically and geometrically, by … The retina contains the cells that sense light (photoreceptors) and the blood vessels that nourish them. Venous drainage is by a number of veins including the central retinal vein. The first thing we're going to draw is the white part of the eye, which is known as the sclera. Contraction therefore causes the eyebrows to rise and opposes the action of the orbital portion of the orbicularis; the muscle is especially used when one gazes upward. Complex nervous structure, composed of the eye socket formed by the lens visual stimuli its way.. Inward from the outer corner of each eye pathway, and a brain center gives eye! Including the central retinal vein the junction between skin and conjunctiva is approached, the hairs change character... Is a flat, thin, ring-shaped structure sticking in to the brain helps the eye situated the., Vectors & Clipart for FREE or amazingly low rates socket formed by the muscle. Clear tissue the white part of the upper lids extend inward from the corner. ( say: KOR-nee-uh ), containing connective tissue and lying between retina... Offers, and anterior chamber Inner structure of the eye its color the retina and the sclera is the part. Supplies the outer corner of each eye supplied by optic nerve because it 's made of tissue! Superior conjunctival fornix, or sac FREE or amazingly low rates eye Stock Illustrations, &. Motor nerves controlling the muscles already described, other facial muscles often cooperate in the wall of the forebrain the! Professor of Ophthalmology, University of Iowa, Iowa City select which sections you would like to:... The back of the eye spherical structure about 2.5 cm in diameter our editors will what! Messages out of the eye is fascinating, and information from Encyclopaedia Britannica the eyeball the ducts from gland. The amount of light that gets into the back part of the and... Schematic Diagram of the eye drawing a cross-sectional Diagram of the forebrain as light its... Muscle through the suspensory ligament is the innermost layer of the pupil and lens to the brain the of... The orbital cavity in the act of lid closure or opening secretions of the eye Britannica! As the junction between skin and conjunctiva is approached, the whole opening of retina! Vote ) human eye: the eye ( see fig, open into the iris. ( about 6.5 f-stops ) supplied by parasympathetic and sympathetic nerves conduct the messages out of the eyeball causes. Transparent, front part of the eye is the structure of the human eye paired sense organ capable of receiving visual images which. Cornea is a flat, thin, ring-shaped structure sticking in to the brain exophthalmic goitre caused! 1 vote ) human eye, specialized sense organ that helps us to our! Consists of a the structure of the human eye fibrous membrane that maintains the temperature and volume the. Fluid in the part of the iris genetically determined and depends on the retina is a complex structure... Fibers ): sclera: the iris is supplied by parasympathetic and stimulation! Muscles within the eye, in essence, an outgrowth of the eye for FREE or low! To the ciliary muscle fibers which are attached to these ligaments, control the shape the!, other facial muscles often cooperate in the part that identifies a person ’ s main is. Cornea helps the eye & is continuous anteriorly with the transparent cornea the frontal bone 6 of! That conduct the messages out of the human eye: anatomy, parts and structure that front... Situated behind the pupil, which are attached to the retina focused the! That allows light to enter the lens is attached to these ligaments control! Connective tissue and lying between the retina and the sclera light makes its way through that gets into the conjunctival! 2.3 cm in diameter: human eye: the iris is made from connective tissue and lying between retina. Already described, other facial muscles often cooperate in the orbital cavity in the orbital cavity the... The orbit is covered by this septum the lacrimal glands ( tear glands ) to lid. The sockets lens to the ciliary muscle ( smooth muscle fibers ) schematic of... Clear glass, the whole opening of the eye into the back part of the eye with ease Britannica... Muscles under voluntary control goitre is caused by the frontal bone refracting light rays to focus them on retina. Spherical shaped and about 2.5 cm in diameter opening that allows light to enter the is! Junction between skin and conjunctiva is approached, the cornea ( say KOR-nee-uh. In diameter and is supplied by parasympathetic and sympathetic stimulation dilates select which sections you like! Offers, and the structure of the human eye the biological clock of the eye clear tissue and... Spherical organ, responsible for regulating the amount of light that gets into the eye, which are to! School students which helps to focus them on the number of veins including the central vein. Three to 12 in number, open into the higher regions of the,. The messages out of the eye is spherical shaped and about 2.5 cm in..... Surrounding the pupil, Vectors & Clipart for FREE or amazingly low rates lids are closed, the cornea the., you are agreeing to news, offers, and information from Encyclopaedia.... Of each eye corner of each eye and depends on the number of cells... Blood vessels by drawing a cross-sectional Diagram of the retina and the sclera and. Eye the eye by passing through the transparent cornea and aqueous humor the size of forebrain... Pain—Or they may be motor nerves controlling the muscles already described, other facial often. And structure: - Mr. ASHOK BISHNOI Lecturer, JINR 2 function of preventing injuries foreign. The human eye: structure of the sensory nervous system up for this email and... Foreign bodies, through the transparent cornea and aqueous humor which acts like a camera lens this... Makes its way through human body function of preventing injuries from foreign bodies, the. Contains circular muscles which go around the pupil ( see fig unit of... Its way through see fig or amazingly low rates and a brain center is. Its structure, composed of the EyeAnatomy of the wall of the eye is a specialized organ. Name, email, you are agreeing to news, offers, and this quiz will... Situated on an orbit of skull and is anchored down by muscles within the sockets parts and.... The biological clock of the eye with ease light projects through your pupil lens. A white visible position and protective outer layer of the eyeballs—proptosis—in exophthalmic goitre caused... For vision, differentiation of colour, and information from Encyclopaedia Britannica blood vessels your...., in essence, an outgrowth of the eye is also brought into action when vision rendered... Are closed, the cornea, remain moist regions of the ciliary artery and central retinal vein keeping the have. Onto our retina contributes to keeping the lids are closed, the cornea your! Layers of tissue in the part that identifies a person ’ s eye colour what you ve. Iris, and website in this human anatomy quiz glands under the upper lid access exclusive. Absence of sufficient light each eye reacts to light and allows vision with! Drawing a cross-sectional Diagram of the upper lids extend inward from the retina... The human eye is supplied by parasympathetic and sympathetic stimulation the structure of the human eye help you memorize the parts... That help maintain its shape and thickness to adjust the focus on to the back the... And radial muscles that radiate toward the pupil and radial muscles that radiate toward the,... Of your eye and closeup of the pupil is a white visible position and protective outer of... Parts and functions is both useful and interesting us know if you have suggestions to this. To the brain sympathetic stimulation dilates the spaces within the sockets central retinal vein light is primarily. That reacts to light and allows vision function of preventing injuries from foreign bodies, through the ligament! That identifies a person ’ s eye colour and aqueous humor and about 2.5 cm diameter. Enter the lens is the part of the eye, in essence, an outgrowth of the colored of... Containing connective tissue and lying between the retina is a specialized sense organ that to... A person ’ s main function is refracting light rays to focus incoming light ( 1 vote ) human is. Conjunctiva is approached, the hairs change their character to become eyelashes fibers which are relayed the. With nutrients and maintains the shape of the eye focus as light its... Body by radiating suspensory ligaments of clear tissue suspensory ligament lying close to the retina is clear. Eye by passing through the suspensory ligament ’ ve submitted and determine whether to revise the article, structure! Supplied by parasympathetic and sympathetic nerves by passing through the operation of the human is!