People always seem to think it's more complicated than it is. Medical
mumbo-jumbo aside, it really is just simple addition. (-4.75) +
(+2.25) = (-2.50)
Maybe this will help. A + value is basically a magnifying glass. So,
since bifocals are just 2 lenses glued together, you have your
distance value (-4.75) and then a magnifying glass (+2.25) glued onto
the front of the lens. The + cancels out part of the -, and you end
up with a higher magnification, even though it's still a - value.
If you have any doubts about the calculations, talk to your doctor or
your dispensary. They'll explain it in (excruciating) detail.
-- Chuck Knight
On Sat, May 30, 2009 at 8:43 AM, DECaM <[email protected]> wrote:
>
> Wanting to order some single vision reading glasses.
>
>
> You say to SUM the SPH and ADD values.
>
> For my right eye these numbers are SPH -4.75 and ADD +2.25.
>
> Would this SUM = -2.50....OR.....some other number?
>
> Not sure how to calculate this....
>
>
>
> Chuck Knight wrote:
>> There are 4 columns of numbers...SPH, CYL, AXIS, and ADD.
>>
>> SPH (sphere) is the amount of correction you need to see, at infinity.
>> CYL (cylinder) is the amount of correction you need for astigmatism.
>> AXIS is how that cylinder should be placed...twisted at what angle.
>> ADD is the extra sphere help that you need, for reading.
>>
>> To make a single vision pair for reading, you do the following:
>>
>> Sum the SPH and ADD values, and enter it into the SPH field.
>> Leave the CYL and AXIS values the same.
>> Leave ADD empty
>> Subtract 3mm from your standard distance PD.
>>
>> That should get you the results you want.
>>
>> -- Chuck Knight
>>
>>
>>
>>
>> On Sun, May 17, 2009 at 5:45 PM, Chris Scott <[email protected]> wrote:
>>
>> >
>> > How do I read my RX to get reading glasses only?
>> >
>> > I've got my current RX, along with measurements taken by an
>> > optometrist a couple of years ago. But I have no idea how to read or
>> > interpret them.
>> >
>> > Any help or explanation would be appreciated!
>> >
>> >
>> > >
>> >
>
> >
>
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