It is not uncommon to see a mild upper eyelid lag for about one to two weeks after cataract surgery. This is in no way permanent. The cause is typically a combination of a swelling reaction by the upper eyelid muscles to the surgery itself and a mild reaction to one of the postop eye drops. The steroid eye drop, which is used for approximately two weeks postoperatively, can cause that upper eyelid muscle to relax a bit while you are using it. Once the steroid is stopped, and a few weeks pass, the eyelids return to normal position. Since cataract surgery is performed on one eye at a time, typically one or two weeks apart, what you are noticing is not an uncommon question. If the difference between the eyes continues then you should discuss this with your cataract surgeon.