OUR MOST IMPORTANT SENSORY ORGAN
The eye is an instrument of precision that enables us to differentiate colours, shapes, movements, speeds and distances, to recognise people and to find our bearings in spaces. Visual stimuli from outside are perceived and converted into electrical impulses. The information is then forwarded to the brain via the optic nerve.
Eighty per cent of the information that we obtain from the outside world is received by our brain via the eyes. The eye works like a small camera with an auto zoom in our head.
HOW DO WE SEE?
In order to see, we first need light. This light consists of electromagnetic radiation that oscillates in different wavelengths. Each wavelength produces a special colour.
If we now look at an object, for instance an apple, the rays of light reflected from this apple hit our cornea where the light is bundled, passes through the anterior eye chamber and strikes the iris. The iris is responsible for the colour of our eyes. If it contains a lot of pigments (colourings), the eyes appear brown; if it contains only a few, the eyes are blue, grey or green.
The pupil is the opening in the middle of the iris. It decides how much light gets into the eye. The pupil adjusts in a similar way to the aperture of a camera: it becomes narrower in bright light, and in the dark it becomes wider in order to capture as much light as possible.
The rays of light then pass through the posterior eye chamber where they strike the lens of the eye. This bundles the incoming light further and regulates it like an auto zoom. It makes it possible for an eye with correct vision to focus from very close-up, to infinity.
The bundle of light then passes through the vitreous body (a gelatinous-like liquid) behind the lens onto the retina. In the centre of the retina, there is an area the size of a pin, the area of most focused vision, also called the macula. In this area, the bundle of light has to converge at a focal point so that the object is perceived clearly and distinctly. If it does not do so, due to myopia, hyperopia or presbyopia, ophthalmic lenses and
contact lenses help us to compensate for this. The retina itself consists, among others, of well in excess of 100 million photoreceptors. There are two types of photoreceptors: the cone cells that are responsible for colour vision and the more light-sensitive rod cells that are responsible for vision at dusk and at night. They convert the light into nerve impulses that are forwarded to the brain via the optic nerve. There, the information is converted into an image (in our case, the apple).
With people who do not have defective vision, the rays of light fall in parallel through the lens and the focus develops precisely on the retina of the eye. In this way a clear image is created on the retina. If the eyeball is too short or too long, defective vision is the result.