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ANATOMY AND PHYSIOLOGY OF EYE

Even though the eye is small, only about 1 inch in diameter, it serves a very important function - your sense of sight. Vision is possibly the most used of the 5 senses and is one of the primary means that we use to gather information from our surroundings. Eye gathers light and then transforms that light into a “picture.” Both also have lenses to focus the incoming light. The eye uses a specialized layer of cells, called the retina, to produce an image. 1. Orbit The orbit is the eye socket, which is formed by the cheekbone, the forehead, the temple, and the side of the nose. The eye is cushioned within the orbit by pads of fat. The orbit also contains the lacrimal gland that is located underneath the outer portion of the upper eyelid. The lacrimal gland produces tears that help lubricate and moisten the eye, as well as flush away any foreign matter that may enter the eye. The tears drain away from the eye through the nasolacrimal duct, which is located at the inner corner of the eye. 2. Cornea The cornea is a clear, transparent layer at the front and centre of the eye. It is a dome shaped  structure. In fact, the cornea is so clear that you may not even realize it is there. The cornea is located just in front of the iris. The main purpose of the cornea is to help focus light as it enters the eye. If you wear contact lenses, the contact lens rests on your cornea.

3. Sclera The white part of your eye that you see when you look at yourself in the mirror is the front part of the sclera. However the sclera, a tough and made up fibrous tissue  also extends around the eye. Sclera surrounds the eye and gives the eye its shape. The sclera is also attached to the extra ocular muscles, which, in turn, move the eye left and right, up and down, and diagonally. 4. Choroid Choroid lies between the retina and the sclera. Choroid made up of blood vessels which provide blood supply to the eye. Just like any other portion of the body, the blood supply gives nutrition to the various parts of the eye. 5. Retina Retina is the third innermost sensory layer of the eye. The light focuses by the lens will be transmitted onto the retina. This is made of rods and cones arranged in layers, which will transmit light into chemicals and electrical impulses. The retina is located in the back of the eye, and is connected to the optic nerves that will transmit the images the eye sees to the brain so they can be interpreted. 6. Macula It is the “yellow spot” in the small central area of the retina surrounding the fovea. It is the area of acute central vision (used for reading and discriminating fine detail and colour). Within this area is the largest concentration of cones

7.Fovea centralis The fovea is the central pit in the macula that produces the sharpest vision. It contains a high concentration of cones within the macula and no retinal blood vessels. 8. Anterior chamber: It is the space behind the cornea and in front of the iris. The anterior chamber is filled with a watery fluid known as the aqueous humor or aqueous. It is produce by a structure alongside the lens called the ciliary body. 9. Posterior chamber: It is the space in the eye behind the iris and in front of the lens. The posterior chamber is filled with a watery fluid known as the aqueous humor, or aqueous. It is produced by a structure alongside the lens called the ciliary body. Aqueous humor provides nutrition to the cornea and lens. 10. Pupil The pupil appears as a black dot in the middle of the eye. This black area is actually a hole that takes in light so the eye can focus on the objects in front of it.

11. Iris muscles The iris is the area of the eye that contains the pigment which gives the eye its colour. This area surrounds the pupil, and uses the dilator pupil muscles to widen or close the pupil. This allows the eye to take in more or less light depending on how bright it is around you. If it is too bright, the iris will shrink the pupil so that they eye can focus more effectively. 12. Lens The lens is a clear, flexible structure that is located just behind the iris and the pupil. It is made up of proteins and water. It is biconvex in nature. It helps to focus light rays into the retina. 13. Ciliary body & muscles: Ciliary body is a ring-shaped tissue which holds and controls the movement of the eye lens, and thus, it helps to control the shape of the lens and help to adjust the focus of the lens. 14. Vitreous body The vitreous body is located behind the lens and in front of the retina. It is filled with a gel-like fluid, called the vitreous humour. It is very thick thus helps to maintain the shape of the eye. With aging it will become thin that will cause retinal damage. 15. Optic Nerve Optic nerves are made up of a bundle of over 1 million nerve fibres. It is responsible for transmitting nerve signals from the retina to the brain and back to the retina. 16. Retinal blood vessels Provide nutrition to retina. 17. Optic disc: The optic disc is the point in retina where all retinal blood vessels attached with retina. It is called blind spot because there are no rods or cones cells so there is no image formation takes place. 18. Uvea or uveal tract: The uveal tract is a layer of tissue located between the outer layer (cornea and sclera) and the inner layer (the retina) of the eye. 19. Extra ocular Muscles: The extra ocular muscles are the six muscles that control movement of the eye. The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction. There are six extra ocular muscles. Superior rectus                           Lateral rectus                                      Inferior rectus Medial rectus                              Inferior oblique                                  Superior oblique

Eye Acessories

1. Eye brows The eyebrow is an area of thick, delicate hairs above the eye at forehead. It prevents sweat, water, and other debris from falling down into the eye socket, but they are also important to human communication and facial expression. 2. Eyelids (bleph) Eyelid is a thin fold of skin that covers and protects the human eye. Upper eyelid of eye is called palpebral and below eyelid is called bulbur. Its key function is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. Moreover, the blink reflex protects the eye from foreign bodies. 3. Eyelashes Eyelashes are the hairy structure that grows at the edge of the eyelid. Eyelashes protect the eye from debris and foreign particles. 4. Conjunctiva The conjunctiva is a thin, clear layer of skin covering the front of the eye, including the sclera and the inside of the eyelids. The conjunctiva keeps bacteria and foreign material from getting behind the eye. It also secretes mucous which help to prevent eyes. 5. Lacrimal gland The lacrimal glands are paired, almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper lateral region of each orbit 6. Lacrimal duct or Nasolacrimal duct The nasolacrimal duct (sometimes called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity.