Symbols associated with vision play a huge role in Animal Dreams. The eyeball dream, Doc's photographs, and the dark cave all mark stages of development in Codi's ability to remember her past and form her own identity.
In a Dark, Dark Room
There are a few scenes in Animal Dreams that take place in Doc's darkroom. Since this is a vestige of the arcane technology of film cameras, we should explain: darkrooms are dark. There are no windows—just a dim red light Doc keeps on while he develops photographs. Doc's way of turning pictures of one thing into pictures of something else entirely already reminds us of the way that he seems to edit his memories—the memory of the flood, for example—to make his actions more fatherly or loving.
Later on, of course, Doc will himself see the link between his practices of developing these photographs and his altering of his own remembered past—sort of. He says that he makes the photographs in order to recreate images from his own memory (13.4). He also says that the idea that the family moved from Illinois is "our myth and every person in Grace believes it, because they want to. [...] If you change the present enough, history will bend to accommodate it" (23.37).
The Eyes Have It
Early on, Codi notices that the process of developing a photograph compares to the mechanics of the human eye. Doc takes photographs of things in the present in order to alter his vision of the past. For that reason, you could say he sees the past everywhere he looks, and then he tries to change the past.
Good luck with that, Doc.
Of course, this never really works: ultimately, the truth comes out, and he has to tell his daughter about her identity. What's amazing, though, is how keeping the truth of the past from Codi leaves her not with a wrong vision of who she is, exactly; it just leaves her with no vision. She's basically blind to her own identity as a consequence.
This blindness is also shown to us symbolically in the first darkroom scene with Codi and Doc. Doc shuts out the lights without warning Codi he's about to do it, and it totally freaks her out: "He knew, but refused to accept, that I was afraid of the dark" (8.59).
It's a moment, very much like Doc, that's both endearing and infuriating. The blackness makes Codi panic, and when she grabs Doc's upper arms in fear, he touches her knuckles to comfort her. It's an odd thing to do, but it's illustrative of the way he has raised Codi all along: he takes away her clear vision of her own past by lying about it, and then tries to fill in the void this creates with his own inadequate version of caring.
The Memory Hole
In the same chapter, we learn for the first time about what Carlo calls Codi's eyeball dream. In it, there's a shattering pop, like glass breaking, and Codi goes blind. It totally terrifies her. We'd be pretty scared, too.
Ultimately, however, the dream is of two things, neither of them all that scary. On the one hand, darkness and blindness are symbolic of Codi's lack of identity. She gets that one figured out when the lights go off suddenly while she and Emelina are standing in a cave. She says, "[T]he terror of my recurring dream was not about losing just vision, but the whole of myself, whatever I was" (17.129).
Memory = vision = identity. Got it?
No? Well, Codi's nightmare of blindness is also key to her eventual reconstruction of the past. It all falls into place when Uda and Codi are cleaning out Doc's attic, and Codi uncovers the image of her own newborn eyes—which have the pure-bred genetic marker of Gracela descendants, in that they're an almost transparently light blue. The dream isn't a prophecy of doom to come, but a memory of birth.
With this knowledge, Codi goes from being someone who can't remember the lady who baby-sat her at thirteen to being someone who can remember being born. It's also no mistake that the dream goes from being one about blindness to being one about light—the explosive light of the flash, and the lightness of Codi's newborn eyes. By learning the truth about her identity, Codi is finally able to fill in the darkness and blankness of her identity with true images of her own past.