The five senses include sight, sound, taste, hearing and touch. Sight, like the other senses is closely related to other parts of our anatomy. The eye is connected to the brain and dependent upon the brain to interpret what we see. Show
How we see depends upon the transfer of light. Light passes through the front of the eye (cornea) to the lens. The cornea and the lens help to focus the light rays onto the back of the eye (retina). The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and then to the brain. The eye works much the same as a camera. The shutter of a camera can close or open depending upon the amount of light needed to expose the film in the back of the camera. The eye, like the camera shutter, operates in the same way. The iris and the pupil control how much light to let into the back of the eye. When it is very dark, our pupils are very large, letting in more light. The lens of a camera is able to focus on objects far away and up close with the help of mirrors and other mechanical devices. The lens of the eye helps us to focus but sometimes needs some additional help in order to focus clearly. Glasses, contact lenses, and artificial lenses all help us to see more clearly. The retina is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. 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. The retina processes light through a layer of photoreceptor cells. These are essentially light-sensitive cells, responsible for detecting qualities such as color and light-intensity. The retina processes the information gathered by the photoreceptor cells and sends this information to the brain via the optic nerve. Basically, the retina processes a picture from the focused light, and the brain is left to decide what the picture is. Due to the retina’s vital role in vision, damage to it can cause permanent blindness. Conditions such as retinal detachment, where the retina is abnormally detached from its usual position, can prevent the retina from receiving or processing light. This prevents the brain from receiving this information, thus leading to blindness. The human eye is remarkable. Although it is small in size, the eye arguably provides us with the most important of the five senses – vision.Vision occurs when light enters the eye through the pupil. With help from other important structures in the eye, like the iris and cornea, the appropriate amount of light is directed towards the lens. Just like a lens in a camera sends a message to produce a film; the lens in the eye refracts incoming light onto the retina, where messages are encoded. The retina, which is made up by millions of specialised cells known as ‘rods’ and ‘cones’, transforms the image into electrical energy and this is sent to the optic disk on the retina, where it will be transferred via electrical impulses along the optic nerve to be processed by the brain. The eyeball contains three layers: • The outer layer, formed by the cornea and sclera The eyeball also contains three chambers of fluid: • Anterior chamber, between the cornea and iris The anterior and posterior chambers are filled with aqueous humour, which is a watery fluid that provides nourishment to the interior eye structures and helps to keep the eyeball inflated. The vitreous chamber is filled with a thicker fluid called vitreous humour, a transparent gel which is 99% water, which helps the eyes to stay inflated.  Did You Know? What makes up an eye?• Choroid: the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light so preventing blurring of vision. The choroid is the spongy middle layer of your eye located between the sclera and the retina. Filled with blood vessels, the choroid’s function is to nourish the outer layers of the retina. View Video • Ciliary body: the part of the eye that connects the choroid to the iris. The ciliary body is located behind your iris, near the crystalline lens. This structure has two functions. The aqueous fluid that fills the front of your eye is made inside the ciliary body. Also, the ciliary body is made up of muscles that allow the eye to focus at different distances. View Video • Cone cells are the second type of light sensitive cells in the retina of the eye. The human retina contains between six and seven million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). It is thought that there are three types of cones, each sensitive to the wavelength of a different primary colour – red, yellow or blue. Other colours are seen as combinations of these primary colours. • Cornea: the transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina. The cornea contains no blood vessels and is extremely sensitive to pain. The cornea is the clear front window, representing one-sixth of the outer layer of your eye. The primary function of the cornea is to focus and transmit light onto the retina. View Video • Conjunctiva: the thin, moist, clear membrane that covers the sclera – the white part of the eye. It is the skin that lines the eye socket and protects and lubricates the eyeball. View Video • Crystalline Lens: The transparent structure inside of the eye located directly behind your iris. The sole function of your lens is to focus light rays onto the retina. View Video • Fovea: forms a small indentation at the centre of the macula and is the area with the greatest concentration of cone cells. When the eye is directed at an object, the part of the image that is focused on the fovea is the image most accurately registered by the brain. • Iris: regulates the amount of light that enters your eye. It forms the coloured, visible part of your eye in front of the lens. Light enters through a central opening called the pupil. The iris is the colored portion of your eye. Located behind the cornea, and in front of the crystalline lens. This structure separates the anterior and posterior chambers of the eye. The function of the iris is to help regulate the amount of light that enters your eye. View Video • Lens: a transparent structure situated behind your pupil. It is enclosed in a thin transparent capsule and helps to refract incoming light and focus it onto the retina. A cataract is when the lens becomes cloudy, and a cataract operation involves the replacement of the cloudy lens with an artificial plastic lens. • Macula: a yellow spot on the retina at the back of the eye which surrounds the fovea. The macula is located roughly in the center of the retina. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such as reading or driving a car. View Video • Optic disc: the visible (when the eye is examined) portion of the optic nerve, also found on the retina. The optic disc identifies the start of the optic nerve where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known as the ‘blind spot’. • Optic nerve: leaves the eye at the optic disc and transfers all the visual information to the brain. The optic nerve is located in the back of the eye. This structure is responsible for transmitting the images we see from the retina to the brain. The front surface of the optic nerve, which is visible on the retina, is called the optic disk. There are millions of nerve fibers that pass through the retina and converge to form the optic nerve. When light hits the retina it is converted into electrical impulses and carried along these fibers through the optic nerve and to the brain. View Video • Pupil: the circular opening in the centre of the iris through which light passes into the lens of the eye. The iris controls widening and narrowing (dilation and constriction) of the pupil. The pupil is the dark center in the middle of the iris. The pupil’s function is to regulate how much light enters the eye. The pupil’s size is automatically varied to regulate the amount of light entering the eye. View Video • Retina: a light sensitive layer that lines the interior of the eye. It is composed of light sensitive cells known as rods and cones. The human eye contains about 125 million rods, which are necessary for seeing in dim light. Cones, on the other hand, function best in bright light. There are between six and seven million cones in the eye and they are essential for receiving a sharp accurate image and for distinguishing colours. The retina works much in the same way as film in a camera. The retina’s function is to sense light and create impulses that are sent through the optic nerve and to the brain. View Video • Rod cells are one of the two types of light-sensitive cells in the retina of the eye. There are about 125 million rods, which are necessary for seeing in dim light. • Sclera: the white part of the eye, a tough covering with which the cornea forms the external protective coat of the eye. The sclera is the white portion of your eye, making up the back five-sixth’s of the eyes outer layer. The function of the sclera is to provide protection for your eye, and to serve as the attachment for the extra ocular muscles which move the eye. View Video • Tear Layer: Understanding the structure of tears is important in order to understand how the tears and tear film provide the eye with a number of specialized functions. Our tears are formed by tiny glands that surround the eye. Tears are comprised of three layers: oil, water, and mucous. The lower mucous layer serves as an anchor for the tear film and helps it adhere to the cornea. The middle layer is comprised of water and the outer layer seals the tear film and prevents evaporation. The tear film serves several purposes. It keeps the eye moist, creates a smooth surface for light to pass through the eye, nourishes the front of the eye, and provides protection from injury and infection. When we blink, the eyelids smooth and spread the tear film so that it is uniform across the surface of the cornea. Excess tears flow out of the eye into two tiny ducts, which then drain into the nasal passage. View Video • Vitreous Body: A clear, jelly-like substance that fills the center of the eye. It is composed mainly of water and comprises about two thirds of the eye’s volume. The vitreous helps the eye maintain a round shape and is attached to the retina at various points, including the macula and the optic nerve. View Video • Zonules: a series of fine fibers that connect the crystalline lens to the ciliary body. The function of your zonules is to hold the lens in place in the eye. What is the name of the layer of light receptors at the back of the eye?The retina is the back part of the eye that contains the cells that respond to light. These specialized cells are called photoreceptors. There are 2 types of photoreceptors in the retina: rods and cones.
What is the thin layer of the eye called?Covering most of the outside of the eye is a tough white layer called the sclera. A clear thin layer called the conjunctiva covers the sclera. At the very front of the eye is a clear surface, like a window, called the cornea that protects the pupil and the iris behind that window.
Which refers to the light sensitive layers of nerve tissue at the back of the eye that receive images and sends them as electric signals through the optic nerve to the brain?The light-sensitive layers of nerve tissue at the back of the eye that receive images and sends them as electric signals through the optic nerve to the brain.
What are the light sensitive cells of the eye?Rods and cones are the light-sensitive cells on the retina. Cones are sensitive to bright light and are capable of colour vision. Rods are sensitive to dim light and give twilight vision. They convert light waves into electrical impulses which are read by the brain.
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The thin layer of light-sensitive nerve cells at the back of the eye is called the
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