Be all eyes
Definition 1 of 1
Pro Tip 1/3Visual Focus
Used when someone focuses their sight on something with high interest or anticipation. 
When the rare bird appeared, the birdwatchers were all eyes.
Pro Tip 2/3Eager Observation
Implies that the observer is excited about what they are watching. 
As the presents were being opened, the children were all eyes.
Pro Tip 3/3Not Literal
It's an expression, not implying the person has eyes all over. It's about attention. 
The class was all eyes when the experiment began.