lack of tears in five month old

[shelbel]

This may sound a bit odd but my five month old ds doesn't really seem to produce tears. He had a sticky eye at birth which rectified itself after a few weeks. If he cries a lot eg over-tired then there may be the odd tear but generally if he cries there isn't. I haven't really been concerned before but i went swimming the other week and he cried all the way through the sessiona and the nursery nurse who looked after the babies suggested he had a temper and was just angry because there were no tears. He has plenty of nappies so i've no reason to think he's dehydrated. Has anyone any suggestions?