Reading glasses are different, only in the values with which they're made.
The rule of thumb is simple. You take the SPH and 1/2 of the ADD, sum them
up, and that's your new SPH. Then you subtract 1mm from your PD, because
the computer screen is closer than infinity.
I know it sounds confusing, so let me give you an example.
SPH +1.50, CYL -0.75, AXIS 85, ADD +2.50
You would calculate (SPH + 1/2(ADD)) = (+1.50 + 1/2(+2.50)) = (+1.50 +
(+1.25)) = +2.75
The resulting prescription would be
SPH +2.75, CYL -0.75, AXIS 85
A negative SPH value is handled the same way...just plug it in and do the
math.
As always, ask your doctor for the specifics, as no two people are exactly
the same, and this is only a "back of the envelope" calculation.
You can confirm the numbers by going to your local WalMart with your regular
glasses, putting a few pairs of readers in front of them (that will simulate
the resulting stronger lens), and trying to read something at arm's length.
That tends to be a good approximation of where your monitor is
located...arm's length.
Hope this helps!
-- Chuck Knight
On Tue, Jun 8, 2010 at 11:01 PM, namalion <[email protected]> wrote:
> Thank you both for taking the time to respond! The info is very
> helpful.
>
> A question for Irene-- are computer glasses different from reading
> glasses? How do you modify your prescription for computer/reading
> glasses (e.g. just subtract a diopter? More?)?
>
> On Jun 6, 5:28 pm, Irene <[email protected]> wrote:
> > Sure. I do it all the time with Zenni, sometimes ordering two
> > strengths in the same order. In my case, that's to get both distance
> > and "computer" glasses. The only time I was asked for a prescription
> > was when Zenni thought I might be filling in the prescription
> > information incorrectly. (I wasn't--I have an extreme prescription
> > and it made sense for them to question it.) In the unlikely case
> > anyone does ask, tell them you're ordering reading glasses.
> >
> > On Jun 4, 4:42 pm, namalion <[email protected]> wrote:
> >
> > > Hi; I'm new to the website and forum. I just got new glasses 3 weeks
> > > ago ("only" $145 after insurance), and they still feel too strong.
> > > I'm correctable to 20/15 vision, but I'd really like a pair that
> > > corrects me to something like 20/40 since I'm mostly just wearing them
> > > around the house in the mornings and evenings when I don't wear my
> > > contact lenses. So my question is, can I order a new pair from an
> > > online glasses maker and just manually input about a diopter less or
> > > so on each lens (I do have a strong Rx, around 8.25 for each eye),
> > > keeping all other numbers the same (I do have a little astigmitism)?
> > > Is this legal? Would the online company ever require me to fax or
> > > mail the original prescription? BTW, I did ask my opthamologist who
> > > wrote the Rx if he could reduce the power but he just tried to
> > > convince me that if I kept wearing the glasses he prescribed, I'd
> > > eventually get used to it. Actually, I'm just using my old glasses
> > > now (at 6 diopters), which are much more comfortable than the new
> > > ones. Any help would be appreciated, as I'm very new to online
> > > glasses ordering!
>
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