The light that is emitted from arc welding will damage your retinas if you do not wear protective goggles. If you've already done this, you should go and see an eye doctor so that any damage can be addressed immediately. This can lead to cataracts or degraded vision later in life.
Agreed with Lance. It'll cause long term problems if you do it more often.
You might get these things called "flash burns" with can damage your eyes pretty badly.