🚀 go-pugleaf

"Dick DeadEye" <anonymouse@yahoo.com> wrote in message 
news:431C9A7C.4000901@yahoo.com...
> 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?

Sphere plus 1/2 the cyl, respecting signs.

So your 1976 Rx  eqiv sphere is (-1.50 ) +  (+3.25/2)  = +0.12 which is even 
closer to -0.50.  It also is about 0.50 undercorrecting your myopia and thus 
it provides some improvement at near as well.

Dr Judy

>
> -"Dick DeadEye"