ok 1st off...a lot of things can cause an appearance of "thinning of optic nerve". glaucoma is the most common, but certainly not the only one. old eye/head trauma could do it, tumors, lot of other stuff.
2ndly, you can have glaucoma w/o having high pressure. "low tension" glaucoma. plus there's angle closure glaucoma where you have spikes in your pressure SOMETIMES, but most of the time you have low pressure. so having a 16 pressure 1 day 1 time doesnt necessarily mean you dont have glaucoma
a "c/d" ratio is short for "cup-to-disc"...its a way of quantifying optic nerve head size & thickness/thinness. so he took a photo & you saw your blood vessels...
i wouldnt be *too* concerned if your doc doesnt sound concerned. glaucoma is hard to diagnose...sometimes it takes years to even figure out a person has glaucoma. you have to monitor the c/d & blind spots & pressures over time to note changes. so you're in the preliminary phase. if you're really concerned: seek a second opinion. there are glaucoma specialists out there who this is all they do.
a GDx would be another good test to have. its a laser retinal thickness scan:
http://familyvisioncare.net/html/services3.htm