What is the ruling on rubbing one's eye and then kissing it, believing that this habit is a way of showing gratitude for the blessing of sight?

No Sunnah or tradition has been reported regarding kissing the hand after rubbing the eye with it. If the one who does it believes it to be virtuous or a means of drawing closer to Allah, then this belief is mistaken. However, if it is done out of habit, then there is no harm in it. The general rule for things is permissibility, but in acts of worship, prohibition applies unless there is a clear permission from the Lawgiver.