The poem is mostly about how the speaker is able to compare what he sees with his eyes to the memory of the scene he's been carrying around in his mind's eye (yes, we just used a metaphor!). The literal eyeball is the barrier between the poet's mind and the scene in front of him. It's not surprising that eyes, both literal and figurative, are important.
- Line 24: The speaker uses the simile of the "blind man's eye" to describe the way he was able to see the river valley in his mind's eye during his long absence. It's a negative simile, though – he says that it's not like a "blind man's eye." In other words, his mind's eye sees things almost as clearly as his real eyes.
- Line 47: The speaker is talking about the calming influence of the beautiful scene at the river Wye. His gaze doesn't dart from object to object in a frenzied way; his "eye" is "made quiet." We could read this as a synecdoche, because it's not just his eye, but his entire mind and body that are "made quiet." So the "eye" is being used to stand in for the whole person.
- Lines 82-3: The speaker is saying that when he was the young, boyish "William," his interest in nature was purely visual. Nature had no "interest" for him that wasn't what he could see with his "eye."
- Line 106: the speaker is saying that the "spirit" (100) in nature connects everything together, which is why he's "a lover" (103) of all natural things that can be perceived with "eye, and ear" (106). But then he goes on to say that the "eye and ear" are able to "half create" the things that they "perceive." Wait, what? Does this mean that our eyes play tricks on us? Well, yes. And the speaker is also suggesting that the "eye and ear" have a kind of consciousness that we're not aware of, so that they "half create" without our even being aware of it.
- Lines 117-9: There's a lot going on in these lines. First of all, the speaker uses the metaphor of "read[ing]" (117) to describe what he thought he could sense from looking at Dorothy's eyes. He also uses synecdoche. He makes Dorothy's eyes stand in for her entire personality. Finally, the speaker uses another metaphor when he talks about the "shooting lights" coming out of her eyes. We have to assume that her eyeballs are not literally shooting laser beams. She's just looking around with such excited pleasure that it's like her eyes are "shooting lights."