Well, when our vision is focused on something, especially light things, we would have blurred vision or headaches, and we would have an eye strain, which could do harm to your eyes. So, I recommend you avoid staring at them for much too long.
Yes, staring at the candle for a long time will be bad for your eyes because of the fluctuating fire. Your eyes vision will be affected if you look at it for a long time. You may find that your eyes may easily get tired. Thus, you are suggested not to look at it for a long time. If you have done so, you'd better use the eye drops to release the symptom.
Well, yes, staring at candle can be bad for your eyes. The macula, which is a very sensitive part of the retina, can be burned out when the macula focuses too long on a tiny dot of light. Also, as we know that the eyes come with a built-in protection. So they do not hold steady very easily. When you stare at a candle, not only do your eyes wiggle, but also the flame flickers. In that way, it will just damage your eyes, leading to a lot of eye problems. So just avoid it.