Its important to know what type of eyelid surgery was performed. If upper eyelid ptosis repair was performed, a subtle change to the cornea can occur when the upper eyelid position changes. This is normal. Once this has stabilized after a few weeks, you can obtain a new prescription for glasses.
If he had lower eyelid surgery, corneal change does not occur. However, as mentioned by Dr. Prendiville, one of the eye movement muscles [inferior oblique], might have become traumatized or swollen during surgery. This will lead to true double vision: you would see two of everything [when there is only one]. This usually resolves, but you do need an evaluation by an ophthalmologist if the double vision lasts more than a day or two.