A Reoccurring Theme - Eyes

From the beginning of Great Gatsby, Fitzgerald writes about eyes consistently. We see this in chapter two, in the valley of ashes, with the billboard of Doctor T.J Eckleberg. I interpreted this billboard as two eyes floating above all the ash, looking down upon the valley. In chapter three, we also see the repetition of the word eyes. “My eyes fell on Gatsby, standing alone on the marble steps and looking from one group to another with approving eyes.” Fitzgerald’s repetition of eyes, whether it is in words or images, is a reoccurring theme that will become more prominent throughout the novel. The billboard of T.J. Eckleberg will become a common image because Nick encounters it multiple times when driving to and from West and East egg. My question is why eyes? I have not seen any other pieces of the book that relate eyes to the plot or characters, so why would Fitzgerald choose eyes as a reoccurring theme?