Modern cataract surgery is one of the safest procedures performed, with a low complication rate; however all surgeries have possible complications. The main possible complications that can affect vision are:
Swelling of the cornea (clear window of the eye). If this does not clear with drops, a second surgery to replace the swollen cornea may be required.
Dropping a piece of the cataract (if the bag holding the cataract is broken). This requires a second operation to remove pieces from the back of the eye.
Infection inside the eye. Requires an injection of antibiotics or surgery.
Swelling in the retina. Requires eye drops for a few extra weeks.
If you have any concerns about side effects, please feel free to ask.