Dan [Radcliffe] was wearing these contact lenses to make his eyes green, and he had an allergic reaction to them.
But Dan’s eyes were puffy and red, and oddly it was quite appropriate for the scene where he was saying goodbye to Hagrid.
I realized I had something special when I first read the book.
His eyes were red and swollen and we had to take them out – we thought we may add that green digitally, though ultimately we decided not to because it felt artificial.