What typically causes pupils to become fixed and dilated?

The phenomenon of pupils becoming fixed and dilated is often associated with pressure on Cranial Nerve III, also known as the oculomotor nerve. This nerve is responsible for controlling most of the eye's movements, including constriction of the pupil. When there is increased pressure on this nerve, it can compromise its function, leading to a failure in the ability of the iris to constrict in response to light. This malfunction causes the pupil to remain dilated and unresponsive, which is a critical sign in various medical conditions, such as head trauma or increased intracranial pressure.

In contrast, increased light exposure typically leads to pupil constriction as a protective response to bright light. Low blood oxygen levels may cause a range of physiological responses, but fixed and dilated pupils are not a direct effect of this condition. Excessive caffeine intake can lead to various reactions in the body, such as increased heart rate and alertness, but it would not typically result in fixed and dilated pupils. Thus, the relationship between pressure on the oculomotor nerve and pupil dilation is the reason why this option is the correct choice.