🚀 go-pugleaf

Dr Judy wrote:
 > "Dick Dead-Eye" <anonymouse@rodent.mx> wrote in message
 > news:4313603B.3070305@rodent.mx...
 >  snip
 >
 > <Then, last Feb ('04), another episode started, this time to the point
 > of causing some mild inflammation:  The distant "wall chart" vision
 > remained relatively close to 20/20, but I needed a magnifying glass to
 > be able to read even regular newspaper size print!>
 >
 > How old are you?  It is normal to start to have trouble with fine
 > print sometime between the ages of 38 and 45.

Yes, I'm right on the edge (currently 39)!  P=)

 > snip
 >
 > <Can the Cyl and Axs have two different values for bifocals or does
 > the bifocal and rest of the glass have to have the same values?>
 >
 > No, you can't have two distance prescriptions and yes, the bifocals
 > cyl and axis is the same in the top and bottom of the glasses.
 > However, by twisting and tipping the glasses you change the effective
 > power and axis.  If you have progressives, there is induced cyl at
 > various points in the lens outside the normal viewing area and by
 > twisting, tipping and reversing the glasses you may well find an area
 > that corresponds somewhat to your prescription.
 >
 > The reason you can see (sort of) in the distance  with your old near
 > glasses is your large amount of astigmatism.  In one meridan your
 > current distance prescription for  is -2.00 and in the other meridian
 > it is +1.00, and the equivalent sphere is -0.50.   Your current near
 > presciption is -0.25 in one meridan and +2.75 in the other, equivalent
 > sphere is +1.25.  Your 1988 near glasses prescription is  -0.25 in one
 > meridan and +2.50 in the other, equivalent sphere is +1.00, virtually
 > the same as required for near.   You can also see that the -0.25
 > meridian is not far off from the +1.00 you need at distance, so by
 > twisting an angling the glasses you could see at distance, although a
 > little blurry.

Did you see my extended, reworked post (which was my intended one P=/), 
with the older "1976" pair:

           news:431A1F1B.7000106@yahoo.com

 >  The recent eyeglass history for my left eye is so:
 >
#> (Sph = "Sphere", Cyl = "Cylinder", Axs = "Axis";
#>  Adj.Sph, Adj.Cyl = Adjusted Sph, Cyl = Sph/Cyl + Add)
#>
#>      Year    Sph     Cyl    Axs
#>      ====   =====   =====   ===
#>  *** 1976?  -1.50   +3.25    80 (Right eye = -1.25  +3.75  105)
#>      1988?  -0.25   +2.75    80
#>      1990   -3.00   +4.00    85    Add    Adj.Sph   Adj.Cyl
#>      2002   -2.00   +3.00    80   =====   ==============
#>      2004   -2.00   +3.00    85   +1.25    -0.75     +4.25
#>      2005   -2.00   +3.00    85   +1.75    -0.25     +4.75

 > Looking at the equivalent spheres (your prescription if the stigmatism
 > was not in the glasses and refraction was done using only spherical
 > lenses) tells the tale:  your distance ES is -0.50 and the old glasses
 > provide +1.00, so you would see about well in the distance with those
 > near glasses as a 1.00 to150 myope would:  somewhat blurry but
 > tolerable.

What is the actual equation for finding the equivalent spherical?

-"Dick DeadEye"