My advice would be not to tell him. You have learnt a valuable lesson and got to know him better as a result of your little prank. You weren't to know why he react the way he did when he lost his glasses, but now you do so you won't do it again. Telling him will cause untold hardship for both you and him....more so him.
I know it is terribly hard when you do some innocent thing like that because you like the attention then find out there is an awful reason behind the persons reaction. But coming clean and telling him will not make anything better. Do something to clear your concences like cook him a nice meal and make a fuss of him.
Perhaps you could tell him how much you like the attention he gave you at that time and work that into your relationship. Men do find it hard to let go and show their softer side...only at times like that will it come through. Encourage him to feel relaxed around you and open up more...then your relationship will grow.