With etymological origin in the Latin word lens , the notion of lens refers to the transparent element used in optical instruments to deflect light rays and allow the formation of images.
Its operation is based on the different degrees of refraction of light rays when they hit the various points on its surface . Thanks to this property, lenses are used to correct vision defects or to capture objects located at a great distance.
A distinction can be made between converging lenses and divergent lenses . Converging lenses cause light rays parallel to the main axis to converge at the same point (the focus of the image). To achieve this, they are thicker in their central sector. Divergent lenses, on the other hand, are narrower in their center and cause the light beams parallel to the main axis to separate.
When speaking at a general level about lenses or lenses (both forms are accepted by the Royal Spanish Academy ), reference is usually made to spectacles or spectacles . These instruments consist of two lenses supported by a frame, designed so that it can rest on the nose thanks to an arch and also be held by the two temples that go to the ears. In this way, each lens (the transparent object) is located near one eye, correcting vision problems.
Contact lenses , on the other hand, are small glass or plastic discs that are placed directly on the cornea . Being convex on one side and concave on the other, they allow the refractive errors of the eye to be solved.
When talking about the differences between contact lenses and glasses, we must not forget the fundamental point: the subject's preferences. There are people who, once they try contact lenses, cannot imagine their daily life with glasses, in the same way that there is a group who does not want to try them or who, after having done so, prefer to keep their glasses for different reasons.
Both positions are valid, and that is why we will see below a list of the advantages and disadvantages of contact lenses compared to traditional ones. Let's start with the advantages:
* Its curvature corresponds to that of the user's eyes, which provides a wider field of vision and reduces problems such as obstructions and distortions so common with glasses;
* They do not hinder sports activities, something that is especially noticeable in swimming;
* For those people who care a lot about their physical appearance , contact lenses are ideal because they are not noticeable and, therefore, should not be combined with other accessories and clothing;
* When it is very cold, contact lenses do not fog up, just as in the middle of a storm it does not matter if they get wet since the eyelids are responsible for "drying" them. With glasses, these two situations pose problems;
* There are contact lenses that alter the appearance of the eyes, both their color and shape, and this can be used to change appearance for aesthetic reasons or to disguise oneself;
* There are some models that modify the shape of the cornea during sleeping hours in case of myopia so that the person can do without any type of lenses for a few hours after waking up.
Among the disadvantages of contact lenses, we can mention:
* the difficulty it poses for certain people to put them on;
* cause less oxygen to reach the eye;
* They are not ideal for jobs that require spending several hours a day in front of a monitor.