The bifocal adjective qualifies that which has two sources. The concept is used in the field of optics with reference to lenses that, having two different powers, allow the correction of vision at long and short distances.
According to DigoPaul, the bifocals, thus, are used by individuals who suffer from myopia (one disorder that affects the focus of objects located a long distance) and presbyopia (difficulty focusing on objects that are close).
Spectacles (glasses) with bifocal lenses began to develop in the late 18th century. American scientist and politician Benjamin Franklin helped popularize bifocals when he grew tired of having to wear two pairs of glasses to fix his near and distance vision defects.
Those original bifocals were made by combining two different lenses in the frame. To focus on near objects, the person 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 small distinct sector that is molded on or within the main lens. Invisible bifocals have even been invented: 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 graduation on the entire surface of the glass and are used to correct all refractive errors, such as presbyopia, astigmatism, hyperopia and myopia..
On the other hand, the engineer Bernard Maitenaz presented the so-called progressive lenses in 1959, a product that has continued to grow and improve since then. 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 providing solutions bifocals, there are still drawbacks that can not be solved. Those with presbyopia, for example, may have trouble analyzing the height and distance of the elements. For this reason, they can suffer falls when walking on uneven terrain or when going up or down stairs.
Every day, more and more experts assure that bifocal lenses are a product that is in decline and that one day they will be completely replaced by progressive lenses. Precisely, bifocals allow to correct near and far vision, but they do nothing with respect to the elements that are halfway, and this can lead to the aforementioned problems.
The abrupt jump that occurs between both areas, the far and the near, inevitably affects the sharpness of all objects that are located 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 of vision, back pain, neck and head.
Bifocals, on the other hand, can be uncomfortable in front of the computer screen. 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.