What lab tests are helpful in figuring out the cause?

[foggyrain]

I'm very new at this. A few months ago, my eyes started getting really red. I have no idea whether it's an allergic reaction or ocular rosacea.

I'll be seeing an opthamologist soon. I'd like to ask my primary care doctor for some lab tests beforehand so we don't waste time on things that can be ruled out. What lab tests are useful to tests for allergies etc?

Thanks in advance!