Staring at anything not just a candle flame long time can cause eye fatigue. In addition, a candle flame itself will not affect the vision; it is not like any screen, which does not have radiation. It is also said that a candle can help you into sleep if you cannot fall asleep within 20 minutes. Please get out of bed, turn all the lights off and light a candle, to concentrate all the attention in the light of candles, turn eyes as the flame swing, and you will feel sleepy later.
Yes, it is bad for your eyes if you stare at the candle flame often. The blinking fire will affect your vision. It may stimulate your eyes nerves. You should avoid such things. The too dark light will make your visual nerves get weak. You'd better protect the eyes by having the bright environment. That is very important.
Candle flame may seen to be week, but it can somehow hurt your eyes. The very sensitive macula of the retina can be burned out if you stare at the light for a long time. No body can look into the sun because the light is so strong. After you staring at the candle flame, and then close your eye, you will see bright spot in your eye. That's because the candle flame had affect your retina. But candle flame is so week and it hard for you to focus on the light all the time. Your eyes will move slightly so it avoid be burned. Compared with sun light, candle flame are so week to burn your eyes unless you have a very bad eye condition.