They are special eye lenses that correct your eye-sight. They correct: distance vision, arm-length vision, and near vision.
They are very useful is you happen to have these eye disturbances. It might be worth the money if you really need to correct your eye-sight. Although I would suggest going to an optician before taking this decision.
You can find more information on this website: http://www.specsavers.co.nz/glasses/progressive-le...
Hope this helped.