Short-sightedness: the reasons behind it and the possibilities to correct it
Visual impairments are widespread - the most common is the so-called myopia, which often develops from childhood on. Fortunately, this type of ametropia is easily corrected. So far, so good - but what happens to the eye whilst looking and being short-sighted? The answer to this interesting question and information on correction can be found here.
What is short-sightedness?
In order to see clearly, the focal point of the lens must lie exactly on the retina in the rear part of the eye. In order for this to work for objects at different distances, the human eye lens can dynamically change its refractive power to a certain extent. If the refractive power of the lens is too high or the eyeball too long, the focus is on distant objects in front of the retina. The result: these remain out of focus even with the greatest effort. Seeing at a short distance, however, still works - consequently, one speaks of someone being "short-sighted".
The maximum distance at which sharp vision is still possible, depends on the degree of myopia. If it is not too pronounced, it is not immediately noticeable in everyday life. Nevertheless, it can lead to problems at school or when in traffic. For this reason, an eye test before starting school makes sense. Either way, it is obligatory in order to obtain a driving licence.
What are the causes of myopia?
There are two different types of short-sightedness: myopia simplex affects about a quarter of the population in industrialised countries. The exact causes are mostly unclear. Both genetic causes and modern lifestyles are thought to be the reasons. The latter include, for example, intensive reading and the use of computers and smartphones. Simple myopia is not considered to be a disease and is generally mild to moderate. The situation is different with the rare, typically inherited degenerative myopia: in this case the visual defect is much more pronounced and usually intensifies with increasing age.
How can short-sightedness be corrected?
In the case of myopia, so-called minus lenses with negative dioptre values (e.g. "-4") are used for glasses. In principle, these are scattering lenses that fan out the incoming light rays. In this way, they counteract the excessive refractive power of the focusing eye lens. They are available in either mineral glass or plastic. Regardless of the material, negative lenses can be recognised by their concave shape: they are thicker at the edges than in the middle, whereby the difference increases with the particular visual acuity. To ensure that the edges still fit into a fashionable glasses frame when the thickness is high, higher refractive glass or plastic versions are available. These allow ultimately thinner cut lenses.
Contact lenses with negative dioptric values may be used as an alternative or as a supplement. Since glasses are fashionable accessories nowadays, the decision is usually made on the basis of functionality rather than aesthetic factors. Contact lenses are adventageous for example, during sports: unlike glasses, they cannot slip off your nose in the heat of battle. They can also be worn together with various sports glasses.