If you were to pick an all-star line-up of poetic images, eyes would be right at the top of the list. We can't think of much of anything that poets like to talk about more. There's all that stuff about how they're a window to the soul, and they come up a bunch in love poems, too. Here, though, they're associated a lot with sleep, with tiredness, and with death. Yipe.
Line 51: The repetition in this line is key to its effect. The sailors are in a kind of drowsy trance, and we think that repeating the words "tir'd" and "eye" (or "eyelids") helps the reader to feel that same sleepy, hypnotized feeling. It's also worth pointing out that these tired eyes are the second half of a metaphor, used as a comparison, to describe the gentle music that the sailors are hearing
Line 100: We think the image of "half-shut eyes" is the perfect way to describe what these sailors want to feel. They don't want to be completely asleep, nor completely awake. They just want to drift and drowse, the way you do in those moments before you fall asleep.
Line 132: Here the "dim" eyes of the sailors are used as an image to drive home how hard their normal lives are. They spend so much time peering at the stars and trying to navigate that their eyes are all worn out. Bad times, indeed.