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.
The advantage of the flat-top bifocal lens.
1.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.
2.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.
The Advantages of round-top bifocals
1.The wearers can see the near things by the round shape and see the distance things by the rest of the lenses.
2.The wearers don't need change two different visions glasses when they both reading book and watching TV.
3.The wearers can keep the same posture when they look both the near thing or far thing.
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Material | NK-55 | Polycarbonate | MR-8 | MR-7 | MR-174 |
Refractive Index | 1.56 | 1.59 | 1.60 | 1.67 | 1.74 |
Abbe Value | 35 | 32 | 42 | 32 | 33 |
Specific Gravity | 1.28g/cm3 | 1.20g/cm3 | 1.30g/cm3 | 1.36g/cm3 | 1.46g/cm3 |
UV Block | 385nm | 380nm | 395nm | 395nm | 395nm |
Design | SPH | SPH | SPH/ASP | ASP | ASP |
How bifocal lens work?
Bifocal lenses are perfect for people suffering from presbyopia- a condition in which a person experiences blurred or distorted near vision while reading a book. To correct this problem of distant and near vision, bifocal lenses are used. They feature two distinct areas of vision correction, differentiated by a line across the lenses. The top area of the lens is used for seeing distant objects while the bottom part corrects the near-vision.