Dilated pupils mydriasis means the black centre of the eye stays larger than usual. This can be temporary and harmless or a sign of nerve or brain problems.
Everyday and medication causes
Pupil size changes all the time with light and focus. Some situations and treatments make the pupils stay wide for longer than normal.
- Eye drops at the optician or eye clinic purposely dilate the pupils for examination.
- Strong painkillers, antidepressants, or allergy medicines can occasionally cause dilation.
- Stress, excitement, or low light naturally make both pupils larger.
- Certain recreational drugs also produce large, slow reacting pupils.
- In these settings vision may be blurry for near tasks and lights can seem bright.
When dilated pupils are worrying
Unequal pupils or dilation with other symptoms may need urgent assessment. A single large pupil can reflect eye trauma, nerve palsy, or raised brain pressure.
- Seek emergency care if a new big pupil follows a head or eye injury.
- Dilated pupils with drooping eyelid, double vision, or severe headache are concerning.
- Sudden light sensitivity, blur, or red painful eye can indicate acute glaucoma or uveitis.
- Children with persistent unequal pupils should be checked by an eye specialist.
- Bring a list of medications to your appointment, as these often explain the change.
