Hi Weiping
There are a few possible different conditions which cause similar symptoms to what you are describing, so it would be difficult to give definitive advice over the internet. What I mean is, your problems might not necessarily be tear duct related.
But in general terms, assuming your problem is indeed tear duct related, blockages may affect the lacrimal canaliculus or the nasolacrimal duct.
Definitive treatment of either of these conditions is surgical, ie 'canaliculotomy' for canaliculitis, and 'dacryocystorhinostomy' for nasolacrimal duct obstruction.
If the ophthalmologists you have seen have not provided a solution, I would advise you to seek another opinion. This is to ensure that firstly, you get the right diagnosis, and secondly, that the right treatment can then be provided for you.
