I'm trying to understand how progressive designs vary by prescription!
INSET
If someone is high minus, they get BI prism when they converge to read, and BO for high plus. Are insets variable on some newer, individualized designs to counteract this, e.g. less inset for high minus?
Are conventional progressives mostly 2mm in, regardless, since a near pd usually= distance pd minus 3-4 mm? Or, does a particular semi-finished progressive blank have an inset that is maximized for the basecurve, knowing that on a +8 base, you are going to end up with +2.00 to +4.00 (whatever)?
FIELD OF VIEW
If someone has higher minus, the field of view through a progressive near zone should be larger, due to minification of the object. Higher plus would have a smaller field of view. Do designers try to keep the near zone constant by moving distortion into the distance with higher plus lenses, or by making the periphery harder, or both, or neither? And can designers, therefore, make a softer periphery for a minus Rx?
ADD POWER
If the add is lower, there is more room to play with for the viewing zones, and less with higher adds. Which designs value distance area the most, and keep it constant, which value near the most, etc.? Do most designers try to keep the proportion of distance to near the same across add powers?
PRISMATIC THINNING
And another thing, what is prismatic thinning? 1-2 pd yoked BU prism to decrease thickness in the add portion? What's that all about? Does that vary with optical labs? Materials? Add powers?
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