XPost: sci.med   
   From: dkcombs@panix.com   
      
   In article ,   
   Eric   wrote:   
   >Quick question about progressive lenses:   
   >   
   >   
   >I think the primary problem is that the critical area of the lens is   
   >done in a narrow vertical strip. There is distortion to the left and   
   >right of that extremely narrow zone. Looking at a line of text on my   
   >computer monitor, the center is readable. The two ends of the line are   
   >blurred. So I have to physically turn my head to read on-screen text.   
      
   I recall, years ago, reading about progressive lens.   
      
   The area of glass that provided clear vision was in the shape   
   of an hour-glass -- fat at the top (distant viewing),   
   *very* narrow in the middle,   
   and again wide at the bottom (for close reading).   
      
   I figured there must be some topological or geometrical   
   or other math constraint that, given the different required   
   curvatures for near and far, determined that hourglass shape.   
      
   A correct explanation of why the hourglass shape would be   
   *most* educational!  Please, someone, have at it!   
      
      
   David   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)