Why don't stores/pharmacies sell negative size eyeglass lenses?

Question

I always see stores such as Target or CVS selling eyeglasses that are +1, +1.50, +3.50, etc etc. They're all "+"!!

Why aren't -1, -1.50, -3.50, etc, sold in stores?

Answer 1

Because the - powers are for distance vision, there are way 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 becomes more critical.

Even those + power reading glasses aren't comfortable for long for those who need readers. The lenses are far from being a good optical quality...they are just basically magnifiers in a frame.

In most people, both the eyes aren't the same prescription either, which doesn't matter all that much for readers that you wear for 10 minutes, but in distance glasses, having the wrong prescription would be very uncomfortable, even dangerous at times.

Getting the right prescription is a lot more complicated than what ready made glasses could possibly ever do.

Answer 2

The glasses sold in the store are for people who need magnification to read...generally those over 40 years of age.  The power needed to achieve that is relatively easy to determine by oneself (though I see people everyday who are wearing stronger glasses than needed...this isn't as hard on the eyes as too much negative power can be, however).  

Glasses with negative powers are to help those who need to see far away.  These are less easy 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 actually needed.  However, this overtaxes the eye muscles and focusing system.  Therefore, the proper amount has to be determined by a professional.