Electric dipole is created from the Action potential between Cornea (positive side) & Retina (negative side) and turns the eye into an electric dipole. And when dipoles move, they cause electric field changes that can be observed. By moving the eyes from left to right or up and down creates an electrical deflection we can measure called an electrooculographic signal (EOG). 

Furthermore you can read in the link bellow, about our EOG experiment and how to do it yourself:

https://backyardbrains.com/experiments/EOG

https://en.wikipedia.org/wiki/Action_potential