Originally Posted by alcheng

... Mr.kenchan, for sure I won't go back to that eyeglasses store anymore or at least they have to redo the job...

Each lenses have an optical center which has the least prism effect, we call that the focal point of the lens.

When the lenses are being cut and mounted onto the frame, we have to decenter the lenses thus the position of that focal point will align in front of the pupil of the eyes when the person is wearing the glasses.

Depends on the prescription, the 'X' mini-meter off from the focal-point-distance will generate an 'X' amount of prism effect, thus the person will feel like 'swimming' when wearing the glasses.

Regarding your experience, your eyes are completely normal (I believe... ), that pair of eyeglasses..... most likely not...