For Each loop on a 2D array in VB.NET

I'm writing a loop to go through the first array of a 2D loop, and I currently have it like this:

For Each Dir_path In MasterIndex(, 0)
    'do some stuff here
Next

But it's giving me an error, saying it expects an expression in the first field. But that's what I'm trying to do, loop through the first field. How do I fix this? What would I put in there?

EDIT: to clarify, I'm specifically looking for the 0th element in the subarray of each array, that's why that second field is constantly 0.