Dilation of the pupil is known as mydriasis and contraction as miosis. Both mydriasis and miosis can be physiological. Side effects include moderate mydriasis, dizziness, sensations of heat or cold, and trembling. Valproic acid can also cause mydriasis, a dilation of the pupils. He reported DMMDA as producing LSD-like images, mydriasis, ataxia, and time dilation. Therefore, dilation of the pupil (mydriasis) is often accomplished with medicated eye drops before funduscopy. The opposite condition, mydriasis, is the dilation of the pupil. Fixed, unilateral mydriasis could be a symptom of raised intracranial pressure. Additionally, ascending reticular activation in cats can produce mydriasis, which can result from prolonged pain. Increased risk of mydriasis was associated with Strattera use in clinical trials. Long term effects of drugs can also cause mydriasis, for example opioid withdrawal. Purposefully-induced mydriasis via mydriatics is also used as a diagnostic test for Horner's syndrome. A fast and short-lasting mydriasis can be induced by ibopamine without systemic side-effects. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs. The mechanism of mydriasis depends on the agent being used.