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Eye Anatomy |
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Eye is the organ responsible for our vision. It is a nearly spherical in shape and contains various parts responsible for the vison.
- Lids: are shutter like muscular organs which cover the eyes and responsible for protection of the eye and also help in keeping the surface of the eye moist by spreading the tear film across the eye.
- Conjunctiva: is a transparent outer layer of the eye which covers the white of the eye and inner surfaces of the eyelids.
- Cornea: is the coloured, transparent clear dome shaped portion of the eye responsible for refraction of light rays, so that they can get focused onto the back of the eye where light sensitive layer called retina is located. It is responsible for the 3/4th of refraction which happens in the eye.
- Sclera: is the white of the eye and the toughest of all structures in the eye.
- Iris: is the diaphragm of muscle situated inside the eye behind the cornea and forms the pupil, a circular opening in the centre of it. It controls the amount of light that enters the eye.
- Lens: is another important part of the eye, again responsible for focusing the light rays onto the retina and is situated behind the iris. This is the part which becomes cataract when it becomes cloudy.
- Retina: is the light sensitive layer of nervous tissue and it lines the eye ball from inside and converts the light sensation into neural electrical stimuli.
- Optic nerve: is the nerve which joins the eye ball to the brain and conducts the electrical stimuli from retina to the brain for processing where it is perceived as an image.
- Choroid: is a layer of blood vessels, sandwiched between retina and sclera and provides the nourishment of the eye.
- Vitreous: is a clear gel like substance, it fills the eye ball cavity and gives the required support to the eye structures, it makes the 80% of the eye. It is a transparent medium and transmits the light rays.
- Macula: is a small area on the back of the eye on retina, contains high concentration of cones (light sensitive retinal cells) and is responsible for the most of the vision.
- Lacrimal gland: is the structure which produces tears and is located at the outer corner of the eye tucked under the lid plate on the eye socket bone.
- Extraocular muscles: are responsible for the movement of the eyes in all directions. They are six in number in each eye and are located on the surface of the eye and attached to the inner side of the socket of the eyeball.
- Orbit: or socket of the eye is the bony depression in the facial skeleton and protects the eye from injury.
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Physiological process of vision
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Light rays from any object enter the eye first through the cornea, the clear dome at the front of the eye and passes through the the pupil. Size of the pupil changes with fluctuations in incoming light. The light rays are refracted (bent and converged) first by the cornea, and then further by the lens, to a point located immediately behind the back surface of the lens. At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).
The light then passes through the vitreous humor, and gets focused on a point on the retina called fovea. The small central area of the retina is the macula, which provides the best vision of any location in the retina. The retina can be compared to a camera, the retina is equivalent to the film inside of the camera, and the lens in the eye is equivalent to the lens in the camera, serving exactly the same purpose of focusing.
Within the layers of the retina, light impulses are changed into electrical signals. They are conducted through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain. Here, the electrical signals are interpreted or “images” by the brain after processing.
Decreased vision or blindness, can occur if there is a break in this process at any level viz. cornea, lens, retina, optic nerve and occipital part of the brain. |
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