Single vision glasses are the main products in the market since their appearance over 8 centuries ago. However, when it comes to the 21st century, varifocal lens, also called multi-focal lens, has become the new fashion and tendency among wearers. Then, some people may ask- what is a vari-focal lens? It is lens with more than one focuses. And here is an introduction about several multi-focal lenses.
In fact, the earliest multi-focal lens can be dated back to the 18th century when Benjamin Franklin had made the first bifocal lens. Therefore, bifocals are the earliest multi-focal lenses. They have two focuses- the far vision and near vision focal. Generally, the upper part lens is for far vision and the lower part for near vision. However, wearers of bifocals find that they can not see clearly of objects at intermediate distance, though they can read and see things in the distance.
Therefore, the great demands have prompted the coming of another special lens- trifocal lens. As it mentioned that wearers can not see objects of arm-length distance with bifocals, trifocals can solve this problem perfectly. Compared to bifocals, they have one more focus- intermediate focal. So there are three vision areas on trifocals, say, near vision, intermediate vision and far vision areas. Henceforth, wearers of trifocals can enjoy great vision clarity.
However, there is a great problem in both bifocals and trifocals- radical vision changes. When wearers of the two lenses move from one vision areas to another, they will have to experience radical vision transition. And some wearers have to endure the pain of dizziness and headaches caused by the radical vision changes.
Then, wearers are in need of multi-focal lenses with natural vision changes.
Later, the birth of progressive lens has eliminated the aforesaid problems. No division lines can be found on this lens. That’s to say, the transition among all vision areas is natural and never radial. Many wearers have benefited a lot from it. Or some always think it seems no lens on their faces with it.
And later, there are also glasses combined by progressive lenses, bifocals and trifocals. They have satisfied wearers with different demands. All in all, multi-focal lens is always in the process of evolution and more achievements will be made in future.