Nowadays, a huge number of both the young and the old are bothered by different kinds of vision problems. Eye diseases are usually serious that fewer people are affected. But on the other hand, visual refractive errors are quite common even among children. Modern kids tend to suffer problems at an earlier age. In general, vision refractive errors include three main types: nearsightedness, farsightedness and astigmatism. Each of them has different symptoms. Nearsightedness usually causes people unable to see distance objects clearly. Farsightedness acts in an opposite way that farsighted individuals have disability to view close up things. Considerably different, patients with astigmatism can not focus a point object into a sharp focused image on the retina. Yet another vision problem is presbyopia, which deprives old individuals’ normal near vision. While all these visual conditions are quite disappointing, there are fortunately various remedies. The most conventional treatment is using prescription eyeglasses. Within this category, there are still several types according to different lens powers. Based on the number of eyeglass lens power, there are mainly single vision glasses and multiple vision glasses. Progressive glasses are quite special belong to the latter type.
Even though some people are advocating that modern laser eye surgeries are advanced enough to permanently cure a common vision problem, corrective eyeglasses are becoming more and more powerful. The first pair of prescription eyeglasses was very likely invented to deal with nearsightedness. This is quite reasonable that corrective glasses in old days were simply single vision ones, which means that each pair could resolve only one kind of refractive error. What is the situation nowadays? While single vision glasses remain as the majority, multiple vision glasses continue to accumulate popularity. The basic concern lying behind is that more and more folks are suffered from more than one vision problem. Among ladies and gentlemen over 40 years old, presbyopia is quite common. For these people, single vision glasses are no longer effective if they still have nearsightedness. Bothered by both myopia and presbyopia, it is necessary to wear glasses capable of correcting both of the two problems. This kind of prescription glasses can be called multiple vision glasses. But in exact, they are bifocal eyeglasses. There are still trifocal eyeglasses which have three focal points, with a third one dealing with intermediate vision zone. However, these bifocal or trifocal eyeglass lenses usually have visible lines on them, which set obvious boundaries. Progressive glasses are more superior that they are equipped with no visible lines. Vision correction is also smoother.
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