The Eye

The eye is a spherical organ which is located in the eye socket. The eye is controlled by six muscles. They are responsible for all eye movements as well as coordinating movement between the right and the left eye. Only when both eyes work together are we able to perceive the depth of an object.

The cornea is located in the front of the eye and allows the penetration of light into the eye. The top layer of the cornea is covered by lacrimal fluid (tears) to keep it lubricated and provide nutrients. In addition the tear fluid ensures a clear and sharp image. 

The conjunctiva is located around the cornea and is a mucous membrane with multiple blood vessels. Underneath the conjunctiva the sclera can be found. This is the white and stiff outer shell of the eye. Behind the cornea the iris can be found. The iris is colored, varying from blue to brown and even a green tint. In the center of the iris there is a hole called the pupil. Muscles inside the iris can contract to enlarge the pupil or make the pupil smaller. Enabling to regulate the amount of light which penetrates the eye. The ocular lens is situated directly behind the iris. Muscles at the edge of the lens are able to cause the lens to bulge.This enables you to see objects close by clearly and is called accommodation. Behind the lens inside the eye a clear jelly filling ensures the eye retains it shape and is called the vitreous. Furthermore there is a constant production and drainage of fluids inside the eye to keep the eye pressurized to retain its spherical shape.

The retina is located in the back of the eye. In this layer are the photoreceptors (the cones and rods) located. The function of the retina is to convert the light into electrical signals which gets transmitted through the optic nerve to the visual cortex in the brain. Where the image is perceived. 

If there is an interference of the light coming to the retina, the vision will be decreased. This  could be caused by a dry tear film or an abnormality such as a scar. In case of cataract, the lens becomes cloudy and you can’t see through it as well as before. At a certain moment, the vision is so diminished that the lens will have to be replaced in a surgical operation.

Deviations in the retina can prevent the photoreceptors from converting the light into a signal for the visual cortex. If there is an abnormality between the photoreceptors and the visual cortex (at the optic nerve or optical pathways), this can also result in the loss of vision. When the function of the eye muscles gets disturbed, the vision will not become blurred but it can cause other complaints such as reduced depth of vision or double images. When one eye is closed or covered, the double images usually resolve.

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The Eye
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