Cynthia, who is right-handed, punches Opie in the eye. However, when he gets home it's not his left but his right eye that's been bruised.
Just after the football incident, Opie runs in through the front door, both eyes are fine. When he gets to his room upstairs, his right eye is very bruised.
When Andy and Helen are arguing about Opie's black eye there's a green chair just inside Helen's front door. When they return from bowling at the end of the show it's been replaced with a TV, and a table lamp. In "The Darling Fortune," her front door is different altogether, reflecting the exterior design usually used for her house.