LOTS of things can cause irritated (and therefore bubbly) eyes other than respiratory infections. Dust or particles in the eyes, a scratch to the eye, eye worms, lice/mites.With respiratory illnesses, you will have multiple birds (of those cooped together or in close proximity) come down with the same or similar symptoms to each other. A single bird will not be affected (unless it is caged alone and far from any others).
There are many respiratory illnesses in addition to CRD; there is no reason you should jump onto the Oh My! It's CRD! just because you suspect a respiratory ailment.