In the past, progressive lenses--those that allow a single clear field of vision from distance to mid-range to near--have been molded on the outside of the lens. More recent technology through which the corrective curve is created on the inside of the lens brings several improvements.
The New Technology
Persona, a Canadian manufacturer of high definition prescription lenses, says that in the case of HD lenses, all of the optics are applied to the inner surface of the lens using precision computer-guided optical polishing equipment.
Why It Works Better
To explain why this works, Persona refers us to the experience of looking through a keyhole. The closer we get our eye to the keyhole, the wider our field of vision becomes. This is true with lenses as well, although the difference represented by the thickness of the lens may be small.
Advantages for Vision
This manufacturer claims putting the optics on the inside increases clarity and reduces distortion by up to 20 percent over conventional progressive lenses.
How We Compensate for a Narrow Field of Vision
Anyone who has worn conventional progressive lenses knows that it is often necessary to move the head in order to change focus from something near to something in the distance and again to focus on something in between. The narrower the field of vision, the more physical adjustments the wearer must make.
HD lens manufacturers say that because these lenses widen the field of vision, wearers experience less of the neck and back strain caused by continually having to aim their heads in order to achieve clear focus.