nope, looking at it from behind, you can use both sides of the ear, well at least I do, his ears aren't THAT big for all the pricking I've needed to do, and he jumps and jerks, sometimes I've wound up slicing right through the edge
more awkward for you to use the front side/inside of the ear, with Panic's dark coat and luxuriant fur -- but I've had to myself, several times when Catcat jerked so vigorously that the poke went all the way through and the droplet on the front side was easier to use (or larger)
I often smear both sides of both ears with Neosporin at night, rub it in gently, so he can heal overnight, he's less likely to wash it away then