At the very beginning of Chapter Two, Nick talks about this face known as Dr. T.J.Eckleburg that looks out over "valley of ashes"(a garbage dump-it was hard to follow). When Nick is describing Eckleburg's eyes, he says the following: "The eyes of Dr. T.J. Eckleburg are blue and gigantic. Their retinas are one yard high." The human eye's retina is at the back of the eye, and can't be seen. The author (F.Scott Fitzgerald) meant irises or pupils.