Over several centuries elapsed since the real

Single vision optical eye wear are the first and most widely used products in the field now. The first real eyeglass wear invented several hundreds of years ago were almost all single-vision, and they were used as vision rectifying devices in most cases. These eyeglasses also take the largest market share in present market. This is firmly related to the features of these glasses. These eye glasses are mainly designed single vision, which is particularly effective in solving some simple eye problems, from which most people are now suffering. In other words, single vision optical eye wear are designed professionally for single vision related eye problems, like nearsightedness, farsightedness and other common vision errors. Multi-focal optical eye wear are specially made for people who are in need of special prescription eyeglasses. Though most eye problems people suffering in their daily lives can be ideally treated with single vision glasses, there are some unique eye diseases that can not be rectified by them, like presbyopia, an age related problem. Therefore, it is needed to create some professional optical eyeglasses- multi-focal eyeglasses. These eye wear have a least two vision focal on each lens. And the firstly multi-focal glasses, namely, bifocals, were said to be invented by Benjamin Franklin in the 18th century. Later, technologies and techniques in the field advance rapidly, multi-focal glasses in other forms arise on and on, like trifocal eyeglasses, progressive eyeglasses, etc. All these above mentioned eye wear are very popular among wearers with both nearby and far vision problems. Of course, much greater achievements will made in the aforesaid two optical eyeglasses as some related technologies and techniques advance rapidly. And it can be said safely that these eye wear will become more and more professional in their functionality in the future and people with particular vision problems can benefit greatly from them as a result.