Context : François Huber was only fifteen years old when he began to suffer from a disease which gradually resulted in total blindness; but, with the aid of his wife, Marie Aimée Lullin, and of his servant, François Burnens, he was able to carry out investigations that laid the foundations of a scientific knowledge of the life history of the honey bee. 
Answer : blindness
What was the sickness that killed François Huber?