Difference Between No

History

Glasses were invented in the mid-15th century, but it wasn't until the 18th century that bifocals were introduced. It would take almost another 200 years for no-line bifocals to be invented in 1959. These lenses came about in part because some wearers found the line between the upper and lower halves of the lens to be distracting. Others were concerned with being perceived as elderly because of their need for reading glasses.

Progressive Lenses

Progressive lenses have multiple powers of magnification sandwiched together in one lens. Their advantage lies chiefly in allowing the wearer to see at all distances, including intermediate distances. However, the reading area is often small and rather distorted due to the size and weight restrictions imposed on the lenses in order to increase the wearer's comfort.

No-Line Bifocals

No-line bifocals have only two powers of magnification: one for seeing objects far away, such as when driving, and one for reading. No-line bifocals can eliminate some of the blurriness associated with the small reading area of progressive lenses, but this comes at a cost: that of leaving objects in the intermediate distances blurry.

Identification

The easiest way to differentiate between no-line bifocals and progressive lenses is to try them on. No-line bifocals have two distinct prescriptions set into the lens, one on top and one on the bottom. You will see a dramatic difference as you move your eyes up and down. With progressive lenses, you will see a very gradual change in prescription from the top of the lens to the bottom as you move your eyes downward.

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