There are hundreds of different designs of PALs made by many different manufacturers. It gets confusing with all the different designs and why are these lenses so expensive? The challenge that manufacturers of these lenses are facing is that as you create a lens that varies in power between the distance optics in the top of the lens and the near power optics needed to give reading vision in the bottom of the lens it creates unwanted distortions in the peripheral parts of the lens.  The goal is the blend the distance and near optics to allow a variable transition zone creating intermediate distance to be in focus as well.  This is difficult to do but they are continually researching better ways to make this peripheral distortion as minimal as possible with improved designs.

The technology that goes into making a high quality variable focus lens is really amazing. The sophisticated optical calculations and manufacturing methods using dual surface computer controlled digital lathes can create lenses that are more comfortable to wear and provide larger zones of optical clarity. The higher the quality of optics - the better your vision can be at distance, near, and every distance in between and with less peripheral distortion. We sometimes refer to the higher quality PALs as digital lenses or free form lenses.  The optical accuracy of digital lenses design can make power changes of 0.01 diopter across the surface of the lens.  This is compared to power changes 0.25 diopters in traditional lens manufacturing.

Everyone has to adapt to the feel of a new prescription when they get glasses.  That adaption can be even more challenging when people try PALs for the first time.  It is a new visual experience and our brains have to adjust.  High quality optics can make this adaption much easier though.

There are less expensive, lower technology progressive lenses available. The visual experience will often be a narrower channel of acceptably clear vision and more peripheral distortions in the lens. This can make adapting to the PAL more difficult for some people.