There are two reasons the operated eye looks smaller
1)Due to excessive light entering the eye.the patient tries to limit the amount of light entering the eye by squeezing the eye(a phenomenon called photophobia)
2)If it was done under local anaesthesia,there is a chance that the eyelid muscle would have become injured.
For more details on complications of cataract surgery visit
http://sites.google.com/site/eyediseases/Home/cataract