● This is a very convenient type of lens that allows the wearer to focus on objects both at close range and far range through a single lens.
● This type of lens is designed to enable viewing of objects in the distance, at close range and in the intermediate distance with corresponding changes in power for each distance.
Bifocal lens can be called a multi purpose lens. It has 2 different fields of vision in one visible lens. The larger of the lens usually has the prescription necessary for you to see for distance. However, this can also be your prescription for computer use or intermediate range, as you would normally be looking straight when you view through this particular part of the lens.
The lower part, also called the window, typically has your reading prescription. Since you generally look down to read, this is the logical place to put this range of vision assistance.
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Advantages of round-top bifocals
The wearers can see the near things by the round shape and see the distance things by the rest of the lenses.
The wearers don't need change two different visions glasses when they both reading book and watching TV.
The wearers can keep the same posture when they look both the near thing or far thing.