I just went to the optometrist and found out that I am nearsighted in one eye and farsighted in the other eye. I was told that I need two pairs of glasses, one to wear while reading, the other to wear while driving or just in daily life. Why can t I just have one pari of glasses with a lens to correct nearsightedness in one eye and a lens to correct farsightedness in the other eye (not bifocals)?