Why don't stores/pharmacies go cynical size eyeglass lenses?
Why aren't -1, -1.50, -3.50, etc, sold contained by stores?
Answers: Because the - powers are for distance vision, there are approach too many different possible combinations of powers possible...and the placement of the optical centers of the lenses to match the optical centers of your own eyes become more critical.
Even those + power reading glasses aren't comfortable for long for those who need reader. The lenses are far from being a good optical element...they are just basically magnifiers surrounded by a frame.
In most people, both the eyes aren't the same prescription any, which doesn't matter all that much for reader that you wear for 10 minutes, but in distance glasses, have the wrong prescription would be very uncomfortable, even unsafe at times.
Getting the right prescription is a lot more complicated than what ready made goggles could possibly ever do.
The glasses sold in the store are for ancestors who need magnification to read...generally those over 40 years of age. The power needed to finish that is relatively easy to determine by oneself (though I see individuals everyday who are wearing stronger glasses than needed...this isn't as hard on the eyes as too much glum power can be, however).
Glasses with negative powers are to support those who need to see far away. These are less trouble-free to determine without the help of an eye doctor, because those younger than 40 can still see through lenses even if they are significantly more powerful than what is if truth be told needed. However, this overtaxes the eye muscles and focusing system. Therefore, the proper amount has to be determined by a professional.
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