It always be a flash since it would be impossible to train the laser on the eye in a moving vehicle. It would be much less than a camera flash. and it would only get one eye since the beam is so narrow.
Hence the word "temporary" - it is common if your eyes are accustomed to a low light condition, like night, that a bright flash will temporarily overwhelm vision.
The beam leaves the laser narrow but widens over distance. Playing with a flashlight can show you how much larger the spot on the wall is than the size of the light. The widened beam means you don't have to have pin point accuracy? Just hit the front. The beam will flash the windows at least. Think street lights or headlights on a dirty car windshield. Greatly reduces visibility.
It isn't about pilots losing their eyes. It is about an aircraft above a populated area unexpectedly having no or little vision.
“The beam leaves the laser narrow but widens over distance.”
It does a bit because the lenses are not that good, but remember that the effective power decreases with the square of the diversion.