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Visual Functions of the Eye

17th January, 2013  

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Once you have decided to go ahead with laser eye surgery, you have decided that your eyesight is one of the most important things in your life and you want to improve it. The procedure can seriously improve your life as it is obvious that eyesight helps you to understand the world around you. Before the surgery, feel free to read about the visual functions of the eye so you have a better understanding of how special your eyes really are.

Many people take for granted how complex their eyes really are. Eyes are designed to read fine print at close distances, are able to see distant objects (within reason) quite clearly, are able to differentiate between different colours (not just black and white), are able to perceive objects around you (not only objects straight in front), are able to perceive well in both dark and light conditions and they can monitor precise movements.

  • The human eye can be compared to a camera which gathers, focuses and transmits light through a lens to create an image of the environment.
  • The image is created on the retina.
  • The lens of the eye bends or refracts light that enters the eye.
  • The cornea also contributes to focusing light on the retina. There are no blood vessels in the cornea because it must remain clear for light waves to pass through uninterrupted. Under the cornea is a cavity containing a nutrient-filled liquid, aqueous humor, which provides nutrients to the cornea and lens.
  • Nerve fibres extending back from the retina’s nerve cells come together behind the retina to form the optic nerve – a ‘cable’ of nerve fibres connecting the eye with the brain.
  • The pupil is the opening that controls how much light passes from the cornea to the lens. The iris, the coloured portion of the eye, is actually two sets of muscle fibres that control the size of the pupil.
    • The lens is the refraction system of the eye; it is located on the other side of the aqueous humor cavity. The lens also contains no blood vessels so that light can pass through unhindered. Light is refracted and focused onto the back of the eye where the nerve endings are present; what is seen may be out of focus if the lens is misshapen or the wrong thickness, resulting in the vision disorders near-sightedness, far-sightedness, and stigmatism. The lens is adjusted by muscles called the ciliary body, which allow light to be focused for distance and movement.
    • Light travels from the lens through a chamber filled with vitreous humor, a semi-solid that helps the eye keep its shape. The vitreous humor is also what holds the retina in place. The retina is the back of the inside of the eye and contains light receptors. The receptors are nerve endings with a direct link to the brain via the optic nerve. Alterations in the vitreal pressure due to eye injuries or diabetes can affect vision and cause retinal detachment or blindness.
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