Does lightened eye color relate to drug use?

Well

latanoprost darkens This medicine can cause your eye colour to gradually change, by increasing the amount of brown pigment in your iris. This is not associated with any symptoms and is not harmful. It predominately happens in people with green-brown, yellow-brown or blue/grey-brown eyes. If the drops are only used in one eye, this may cause your eyes to permanently become different colours. Ask your doctor, eye specialist or pharmacist for more information.

This drug is used in glaucoma.