Planet Earth and Its Environment A 5000-million year Journey

Biology in Focus, HSC CourseGlenda Childrawi, Margaret Robson and Stephanie Hollis

CommunicationTopic 3: The Human Eye1DOT Point(s) describe the anatomy and function of the human eye, including the: conjunctiva, cornea, sclera, choroid, retina, iris, lens, aqueous and vitreous humor, ciliary body, optic nerveexplain how the production of two different images of a view can result in depth perceptionIntroductionSite is a sense that is involved in communication, enabling an organism to receive information in the form of visual stimuli. These visual stimuli, in the form of light, are detected by sensory cells called photoreceptors in the eye.www.africadreamsafaris.com

IntroductionThe eye functions as a sense organ by detecting light stimuli from the environment and transforming this information received into nerve impulses that are carried to the brain. This is where the information is interpreted as a picture. somsville.wordpress.com

Accessory Parts of The EyeHumans have two eyes for binocular vision. This involves the two eyes moving in a co-ordinated manner to perceive stimuli. Associated with the eyeballs are accessory parts that are not directly involved in vision but help maintain adequate functioning of the eye.about--eye.blogspot.com

Accessory Parts of The EyeEach eyeball is situated in a funnel-shaped cavity in the skull called an orbit. The orbit is lined by fatty tissue that protects all parts of the eyeball, excluding the exposed front. legacy.owensboro.kctcs.edu

Accessory Parts of The EyeThe front of the eye is protected by a thin, transparent membrane called the conjunctiva. This membrane is continuous with the inner layer of the eyelid. The eyelid is made od muscle and skin and provides further protection for the front of the eye.www.takechargemama.com

Accessory Parts of The EyeA lacrimal, or tear gland, on the upper, outer corner of each eyeball secretes liquid tears that keep the exposed surface of the eyeball clean and moist.www.umm.edu

Depth PerceptionWhen eyes face forward, each eye sees an image of an object in the light path. The two images are fused into one image in the cerebral cortex of the brain. This fusion into one image is related to the perception of depth but is a different phenomenon.

Depth PerceptionDepth perception is the sense of depth that occurs when objects are viewed with binocular vision (vision which both eyes are used together). We say that a person has steroscopic vision; that he or she is viewing the world in three dimensions. www.eyehealthweb.com

Depth PerceptionStereoscopic vision depends on the fact that the two eyes are separated horizontally so they have slightly different views of objects located at different distances away. When an object is a slightly different distance away from each eye, it is imaged by each eye at a different distance from each fovea. This gives the perception of depth as this image is fused and seen to be a different distance from the eye to another object that is closer to the eye.

Depth PerceptionFor example, the object R and Q in this diagram would be seen as being two different distances from the eye. They are focused in different places on the retina, seen as two images in their respective positions and so there is depth to the picture that is perceived. https://en.wikipedia.org/wiki/File:Binocular_vision.svg

Structure and Function of The EyeThe eyeball is surrounded by a coat, made up of three layers of tissue: an outer, middle and inner layer. In a developing embryo, each structure within the eye develops from tissue in one of these three basic layers. The position of these structures within the eye are easier to remember if they are described in in relation to the layer in which they originated.

The Outer Coat of The EyeSclera: The sclera is the outermost layer of the eye. Towards the back of the eye (posteriorly), the sclera is opaque, forming the white part of the eye. As you continue forward (anteriorly) it becomes a transparent structure called the cornea.

The Outer Coat of The EyeThe sclera is composed of a tough, non-elastic tissue that protects the delicate inner layers of the eye and it helps to maintain the shape of the eyeball. It is also the site of attachment for the external muscles of the eye, which enable the eyeball to move in the socket.www.studyblue.com

The Outer Coat of The EyeCornea: The cornea contains no blood vessels and is completely transparent to allow light to enter the eye. The curvature of the cornea helps to bend or refract the incoming light rays so that they converge and land at the back of the eyeball on the inside. The cornea is very well supplied with nerve fibres that are sensitive to touch and pain.www.retinamd.com

The Middle Coat of The EyeChoroid: The middle coat of the eyeball is the choroid layer. Most of the blood vessels of the eye are in this layer. Posteriorly, the choroid layer is black, reducing the scattering or reflection of light within the eye. Anteriorly, the choroid layer continues forward to form the cilliary body and lens. In front of this is the iris. www.stlukeseye.com

The Middle Coat of The EyeWhere the sclera continues forward as the cornea, you will see that the retina ends and the choroid layer thickens to form a ciliary body.

Ciliary body: In three dimension the ciliary body forms a ring around the front of the eye and contains the circularly arranged ciliary muscles. cancerinfo.tri-kobe.org

The Middle Coat of The EyeThe ciliary muscles attach to the lens by suspensory ligaments.The muscles and ligaments are important in adjusting the curvature of the lens for near and far vision. Well look at this in greater detail a bit later.

www.apsu.eduThe Middle Coat of The EyeThe chambers inside the eye are filled with fluid of differing consistency. Aqueous humor: a transparent, watery fluid found in the anterior part of the eye between the cornea and the lens. ehealthmd.com

The Middle Coat of The EyeIt provides nutrients for the lens and cornea which do not have their own blood supply and has a composition similar to that of blood plasma and. The ciliary body is responsible for secreting the aqueous humor.www.geteyesmart.org

The Middle Coat of The EyeVitreous humor: a clear, jelly-like material filling the remainder of the eyeball (the part behind the lens and enclosed by the retina. The vitreous humor contains dissolved nutrients, refracts light and helps to maintain the shape of the eyeball.toadhaven.com

The Middle Coat of The EyeLens: a transparent structure made of cells enclosed in a membrane called the lend capsule. The lens refracts light rays and directs them onto the retina where a focused image will be formed.www.laurenscharff.com

The Middle Coat of The EyeThe lens has highly elastic properties that enable it to change shape, varying from a rounded to a flatter structure. This allows the eye to accommodate for near and far vision respectively. The lens is biconvex in shape bulging outwards.

The Middle Coat of The EyeIris: the coloured part of the eye situated between the lens and behind the cornea. It is surrounded by aqueous humor. The iris contains the pigment melanin, also present in skin and hair. The colour of the eyes is determined by the amount of melanin in the iris. Blue eyes contain little while darker eyes contain more.www.accessexcellence.org

The Middle Coat of The EyeStructurally, the iris is made up of connective tissue and smooth muscle. One set of muscles is in a circular arrangement and the other set is arranged radially. These muscles bring about the main function of the iris, which is to control the size of the pupil.

The Middle Coat of The EyePupil: an opening in the iris through which light rays pass to reach the retina at the back of the eyeball. When the circular muscles contract, they squeeze inwards, causing the pupil to constrict, letting less light into the eye. This is kind of like a purse string that is pulled to close off the top of a bag. www.miracleintheeye.com

The Middle Coat of The EyeWhen the radial muscles contract they pull outwards and as a result the pupil dilates and allows more light to enter the eye. The size of the pupil therefore directly determines the amount of light that can enter the eye. www.takechargemama.com

The Inner Coat of The EyeRetina: lines the posterior two-thirds of the eyeball and is extremely thin and delicate. It contains photoreceptors for vision.Its approximately 1/10mm thick. If examined microscopically, it is seen to contain several layers of nerve cells. www.theeyesurgicenter.com

The Inner Coat of The EyeThere are two types of photoreceptors (light sensitive cells), the rods and cones positioned closer to the choroid side of the retina. The rod and cone cells are present only in the posterior part of the eyeball where the incoming light can reach them.www.rhsmpsychology.com

The Inner Coat of The EyeFovea: a particularly sensitive part of the retina, found in an area called the macula or yellow spot. It is the area of most acute vision. The macula contains a greater number of cone cells than the rest of the retina.www.stlukeseye.com

The Inner Coat of The EyeThe fovea appears as a depression in the centre of the macula of the retina at the back of the eyeball, and is directly opposite the incoming light. It contains numerous, densely packed cone cells but no rod cells at all. sites.google.com

The Inner Coat of The EyeBlood vessels are absent and there are no layers of nerve fibres between the photoreceptors and the incoming light in the fovea, differing from the remainder of the retina in this way. The fova is the part of the retina where the greatest detail can be detected.medcell.med.yale.edu

The Optic Nerve The blind spot is an area of the retina where all the nerve fibres leave the eye and converge to form the optic nerve. Blood vessels also leave the eye at this point. Because there are no rod and cone cells in this area, light that falls on this part of the retina cannot be detected, leading to it being named the blond spot.www.goiit.com

Blind Spot ActivityTurn your books to a clean page and make a circle and X about 4-5cm apart.

X

Close your left eye and hold this page out in front of you with the dot in front of your right eye. Concentrate on the dot with your right eye and slowly bring the paper towards you. When the image of the X falls on the blind spot, it will dissappear.Dilation and Constriction ActivityWorking in pairs: Dim the light in the classroom. Have one partner cover their eyes with cupped hands for 2 minutes. After the time has lapsed, uncover your eyes and let your partner observe the change in your pupils.Switch roles

Homework-DOT Point??????????????/