For the first time, police officers on Monday gave a public moment-by-moment account of accused Aurora shooter James Holmes' arrest, as part of a hearing that touched on whether Holmes is mentally fit to stand trial. Officer Jason Oviatt described Holmes as "very relaxed" after the shooting, noting that Holmes had extremely dilated pupils. Are dilated pupils a sign of mental illness?

Not a good one. Dilation of the pupils can reflect not just the lighting conditions in a room but the thoughts and feelings of a person, mentally ill or not. For example, dilated pupils can indicate sexual arousal. Psychologists sometimes study the expansion and contraction of the pupils to find an objective measure of the mind's inner processes, in something called pupillometry. This practice has been used to study everything from racial bias to sexual preference to what happens when the mind puzzles over a difficult math problem.

However, while pupillometry has been used to study aspects of mental illness, including schizophrenia, and while psychologists began observing pupil dilation among the mentally ill more than 100 years ago, pupil dilation on its own is not a good indicator of psychosis or other mental illness. Pupil dilation is regulated by the sympathetic nervous system, the part of the body that controls our fight-or-flight response. So even when psychosis causes changes in pupil dilation, such as by triggering an excited state of fear or anger, the dilation itself is identical to dilation in the non-mentally ill. Moreover, just as with sane people, the pupils return to normal once the state is over.

Dilation of the pupils can also be a side effect of using certain drugs. For example, LSD and mescaline both cause pupil dilation. Some people who suffer from mental illness may find themselves with dilated pupils caused by treatment with prescribed antipsychotic medications.

In the search for more objective, physiological signs of schizophrenia, other aspects of the eyes have also been studied, with mixed results. At least one study purported to find particular groups of facial features, including small eyes and narrow openings between the eyelids, in two subgroups of schizophrenics, but most psychiatrists don't think such findings are useful. Researchers in the United Kingdom recently developed a computer model that could separate out a group of schizophrenics by tracking abnormalities in the movement of their eyes. However, so far the test isn't accurate enough to be used for diagnosis.