This scene from Heat is great for studying eyes.
Things to watch for:
•How their eyelids follow their eye movement
•How Al Pacino intensely stares with little eye movement
•How Robert De Niro looks away when he’s thinking, and how he’ll blink to look in another direction
•At 1:09 De Niro uses his eyes to point down when he says “we’ve been face to face” Your character doesn’t have to have a dramatic gesture or use their finger to point. This small gesture is far more interesting and not a cliche choice.