I am not sure if this will make a difference in finding family connections or not but we have never pronounced our name "lie den" as I have heard most others.
Also, I am doubting that "Van Leyden" is related to the Irish, though it is just a hunch. If anyone has info on this please let me know.
... and then there is Leyden, Holland. I don't know the connection if any but I have tried to research it without any luck. I have thought that the Irish Leyden name was anglicized from the name "O Loideain" and then took on different forms. I dont' know how Holland came up with their Leyden name. Anyone out there know?