What aspect of the eye changes as a sign of death?

The flattening of the eyeball is a notable change that can occur after death. This process is linked to the loss of muscle tone and the withdrawal of blood from the surrounding tissues, which results in the eye's shape modifying from its normal spherical form. After death, as the body begins to cool and the eyelids might remain open, the contents of the eye can lose pressure, leading to a more flattened appearance.

In contrast, pupil constriction typically occurs during life and is associated with certain reflex responses. Increase in eye moisture is unlikely since, after death, there is a cessation of bodily functions that would maintain moisture levels. Redness of the conjunctiva is also not a change that signifies death; it is more commonly associated with irritation or inflammation while an organism is alive. Hence, flattening of the eyeball serves as an indicator of the changes that occur post-mortem.