SEE RELATED: Eye dilation FAQs Benign episodic unilateral mydriasis This slows your eyes' ability to react to light. However, the substances themselves do not cause your pupils to dilate.Ī number of illegal drugs, however, do directly cause dilated pupils. This effect can last two hours or longer after drug ingestion. Research has shown that alcohol and marijuana - separately or in combination - can reduce your eyes' ability to recover from exposure to a bright light source (such as oncoming headlights at night) and adapt to changing light conditions. This is why you see physicians checking an athlete's pupils with a penlight following head trauma sustained during sporting events, or when a patient arrives at a hospital emergency department with other possible stroke symptoms. Brain injury or diseaseĪ head injury, stroke or brain tumor can affect how your pupils react to light and cause dilated pupils. Sometimes, this sort of injury can occur during an eye surgery, such as a complicated cataract surgery or a corneal transplant. READ NEXT: Floppy Iris Syndrome Eye injuryĪ serious, penetrating eye injury can damage your iris and cause the pupil to become dilated and irregular in shape.

The following prescription and non-prescription medicines can cause your pupils to dilate and affect their ability to react to light:īotox and other medications containing botulinum toxinĪtropine (used for myopia control and other medical purposes) The most common dilated pupil causes include: Medications If one pupil is noticeably larger than the other, you may have something called anisocoria. Your pupils should also dilate symmetrically. However, if your eyes are fully dilated even in a bright environment or if your eyes don't seem to be dilating as they should, it's time to get your eyes checked. It's normal for your pupils to dilate more the darker your surroundings.

If you've noticed your eyes are unusually dilated (larger) or one eye is dilated more than the other, call an eye doctor!

Fixed dilated pupil