Shining a flashlight in your own eyes or someone else's eyes should not damage your eyes or cause permanent blindness.
However shining a flashlight in your eye or someone else's eye can cause a temporary blindness but the temporary blindness should go away within a few minutes.
I've had flashlights shined in my eye several times as a kid and nothing bad happened.
I temporarily lost my sight but it only lasted for a few minutes at most and then I was able to see again.
I still have very good eyesight now.
Shining a flashlight in an attackers eyes can help temporarily blind the attacker or even a flashing light is much better.
But you should still get away from the attacker.
But as for shining a flash light in your eye most flash lights are not powerful enough to cause any permanent blindness.
But it's still not good to shine the flash light in your eyes anyway.