This is a controversial issue.One theone hand, some folk think that flash photography may be hurt to your eyes, because it can lower the sensitivity of your eyes; On the other hand, some eye doctor say that flashes are not dangerous to your vision,they can cause headache or be uncomfortable. As far as i can see, this is the problem of degree, you will be ok if you can control they in a certain range.
Yes, the flash photography is bad for the eyes to some degree because of the moving pictures. It can affect your eyes vision from the radiation. You need not to see it often and in a long time. You should have the rest for the eyes now and then. If you feel something uncomfortable for your eyes, you could use the eye drops to release it.
Obviously, the possibility of your eye injury increases when they are exposed to brighter light for a long exposure times. Well, our eyes are highly connected to our nerves. And nerve cells communicate with each other by electrical signals. As we all know, our eye dilated when we go from indoor to outdoor making more of the cornea to be exposed to air. Then the light will come into some sensitive cells directly in our eyes leading to pain or a vision full of small black spots. That is why we are advised to close our eyes to adapt to a lighter condition when we passing through any tunnel by train. If the light is strong, it carries a large information for our eyes to transform. In order to accept, our retina deals with a lot of work and it will become sensitive and vulnerable each time. Limit the lasting time and the frequency that you take photos. Don't worry, few will be acceptable. Never forget we also have our protective mechanism.