Sclera

The choroid is a highly vascularised, darkly pigmented layer found in between the retina and the sclera of the eye.

The eyes may remain open for such long periods of time that the conjunctiva and sclera may become quite dry and ulcerate.

She'd been back a week and it was clear that college-level track was kicking her ass, the sclera in her normally wide manga-eyes were shot through with blood vessels.

Such pressures explain why humans are peculiar in having our rather small irises set against a white background—the sclera—in our eyes. Anyone watching us can infer where we are looking or whom we are looking at.