Washiken uchi (literally: “eagle-fist strike”) is sometimes referred to as a chicken-head strike.
Chicken-head strikes are an oddly-specific atemi, used to crush an opponent’s eyes. As such, chicken-head strikes are forbidden to use in kumite. Chicken-head strikes can be thrown from a variety of odd angles to the inside, outside, and straight-forward. Since it doesn’t take much strength to crush an eye, this is one of the few techniques than can be reliably called upon if your balance has been compromised.
To perform a chicken-head strike, bunch your fingers together, as though you were an Italian-American stereotype. Then, pretend your hand is a bird's beak, which pecks your opponent’s eyes out.
[Photo of chicken head hand position.]
[Chicken heads fast and slow, from the front and side, inside, outside, and forward ]
This technique is reserved for advanced students -- not because it is difficult, but because there are more important things that up-and-coming karateka should be worried about.
Please note that this technique crushes eyes like were grapes; it does not pluck them out of people's heads, like in Kill Bill.