The adjective bifocal qualify what has two spotlights. The concept is used in the field of optics with reference to lenses that, having two different powers, allow the correction of long and short distance vision.
The bifocal lenses, in this way, they are used by individuals who suffer myopia (a disorder affecting the focus of objects located at a long distance) and presbyopia (Difficulty focusing on objects that are close).
Spectacles (spectacles) with bifocal lenses began to develop in the late century XVIII. The American scientist and politician Benjamin Franklin helped popularize bifocals, when he got tired of having to wear two pairs of glasses to fix his flaws in the view near and far.
Those original bifocals were made by combining two different lenses in the frame. For focusing on close objects, the person He had to look at the lower sector, while to focus on distant objects he had to focus on the upper part.
Currently, bifocals usually consist of a sector small differential that is molded on or within the main lens. They have even invented invisible bifocals: in them it is very difficult to notice the different lenses installed on the glasses in question. Many consider the classic models unsightly, precisely because it is possible to notice the part in which the graduation is placed closely.
It is important to note that bifocal lenses exist as an alternative to monofocal lenses, which have the same prescription throughout the entire surface glass and that are used to correct all refractive errors, such as presbyopia, astigmatism, hyperopia and myopia.
On the other hand, the engineer Bernard Maitenaz presented in 1959 the so-called progressive lenses, a product that has continued to grow and refine ever since. It is an alternative to bifocals, which allow the user to perceive their surroundings in a more natural way, with an adequate transition between near and far objects.
Beyond the solutions that bifocal lenses provide, there are still drawbacks that cannot be resolved. Those with presbyopia, for example, may have problems to analyze the height and distance of the elements. This is why they can fall when walking on uneven ground or going up or down stairs.
Every day, more and more experts assure that bifocal lenses are a product in decline and that one day they will be completely replaced by progressive ones. Precisely, bifocals allow to correct near and far vision, but they do nothing with respect to the elements that are in the middle of the road, and this can lead to the aforementioned problems.
The jump abrupt that occurs between both areas, the far and the near, inevitably affects the sharpness of all objects in the middle, something that does not happen with progressive lenses.
Another of the negative points of bifocal lenses is the difficulty to get used to them during the first uses; Among the “symptoms”, so to speak, are discomfort in the eyes (such as tearing, stinging, irritation and itching), distortion vision, back, neck and head pain.
Bifocals, on the other hand, can be uncomfortable in front of the screen of the computer (computer). This drawback arises from the fact that the monitor is usually placed very close to the user, which forces him to tilt his head back to be able to clearly appreciate the content; After long sessions, neck discomfort may appear, which can worsen if not treated in time.