3
This theory is based on the glimpses of Doffy's childhood we get. While strung up one of the methods of torture mentioned involved blinding someone. The next panel shows an arrow being shot towards Doflamingo. We then suddenly get an image of two eyes as he wakes up, one without shades and one with shades with a reflection of fire in them.
But note that ...
Only top voted, non community-wiki answers of a minimum length are eligible