Henry Lim's eye was blinded on a construction site before the events of the book. He loses vision in that eye and tells Jet he's going blind in his oypther eye the first time she visits his house.
Nina Smith was 16 at the time of her suicide. Emily Mason was 16 at the time of her death. Both are only discussed as memories, though Emily's Drowning gets a lot of detail later on.
Jet's vision begins to distort about halfway into the book, giving her double or quad vision. Reality doesn't change, but she talks about seeing two or four of things when there is only one.
Jet's skull is smashed in ch. 1. She visits the crime scene in ch. 2 and the blood pool + splatter is described in detail. Billy changes Jet's bandages in ch. 12 and some description is given.
In ch. 33, a man is shot at close range. His blood is described.
Jet's sister, Sophia, drowns before the events of the book. Jet talks about it with Billy in ch. 14. The Drowning is later described in detail in ch. 28.