When you buy varifocal spectacles, you can choose between basic, better and 'best' performance. The more you pay, the wider the field over which they work satisfactorily. I once bought some of the cheapest and found that they only worked when looking straight ahead. I have since paid more and my present ones are much better; I can scan a scene by just moving my eyes rather than having to use my neck muscles. They are very good, actually - just a ludicrous price. What could be the reason for the various available 'qualities' - apart from an artificial commercial ploy to increase company profits. I assume that a computer program will generate the appropriate profile and the lenses can be produced on a mill (?) of some sort. Are the posh ones made of a different plastic?