How is it possible that after the treatment I need reading glasses that I didn't have before the treatment

If you are older than 45, it is common that your own eye lens is no longer flexible enough to focus over a well-corrected eye.

We often use a trick to keep reading by taking off glasses from a distance or looking under the glasses. This makes it seem like you don’t need reading glasses. But you do have that, because you look less closely with your glasses than without your glasses.