Well dealing with "c" we'll first have to figure out exactly what the hell a photon is and does it really exist in our three-dimensional spatial/one dimensional temporal universe. "c" = speed of light, light = photon, speed of light = time dilation maximum (time stopped)/ length contraction maximum (distance zero). It would appear to me that time and distance does not exist for a photon in "flight", therefore it does not exist in our 3Dimen/1temp dimen universe.
If it does not exist in our 3Dimen/1temp dimen universe, wouldn't it be uneffected by any medium that is within our 3Dimen/1temp dimen universe?