For how long after the retinal detachment surgery should i be wearing the plastic eye shield to sleep?

It varies: The purpose is so you don't accidentally bump or rub your eye during sleep. It varies from doctor to doctor: a few days to a week or two. It also depends on how quickly you heal. Ask your retina specialist.

^6 months: This is just to give rest and protection to your eye.

Up to 3 weeks: Small wounds are sometimes made in the eyeball during retinal detachment surgery. The eye shield is used to protect the eye while it is still fragile during the early stages of healing. This protects it from accidental trauma or rubbing, particularly during sleep.