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Human vision
The eye > Human vision

Human vision

Vision is a process

The eye is the organ of vision. From a physiological point of view, vision is a process of sensorial perception which captures our outside environment and transforms it into internal images that can be interpreted by our brain.

For our eyes, the outside world, its shapes and its colours are made up of light rays. Once detected, these rays converge within the eye to project onto a limited area of the back of the eye, an area that works like a projection screen on which the images are formed then transmitted to our brain.

A 4 step process

Four basic elements of the eye participate in this process:

the iris is the coloured part of the eye. Just like a camera, in the pupil the iris has an aperture mecha-nism enabling it to regulate the amount of light entering the eye.
the crystalline lens plays the role of a converging lens. This type of lens transforms parallel light rays into converging light rays towards a central point. So the crystalline lens makes the light rays detected by the iris converge towards a central point of the retina, located at the back of the eye.
the retina plays the role of a projection screen on which images are formed. It is made up of elements very sensitive to light that are called cones and rods.
the optic nerve transmits the retinal images in the form of nerve impulses to the brain which interprets them.

Vision problems

To a great extent, the eye can to a great extent be likened to an optical instrument. But this instrument may experience some defects which cause vision problems. The most well known are short-sightedness or long-sightedness.

EMMETROPIC

When vision is normal, we are emmetopic. In this case, and as the figure shows, the light rays are perfectly focused on the retina.

Emmetropic
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SHORT-SIGHTEDNESS

Whereas, in the case of short-sightedness, when you see better close up than far away, the eye is too long, and the light rays meet up in front of the retina.

Short-sightedness
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LONG-SIGHTEDNESS

Lastly, in the case of long-sightedness, where you see better far away than close up, the situation is reversed: the eye is too short, and the light rays meet up behind the eye.

Long-sightedness
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The optical defects of the eye can be corrected

either by using other optical instruments, such as glasses or lenses.
or by surgical intervention: in this case the problem is dealt with at source.

BRUSSELS EYE DOCTORS, BD SAINT-MICHEL 12-16, 1150 BRUSSELS – TEL. + 32 2 741 69 99