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 a doctor checking an athlete's pupils with a pentorch following head trauma sustained during sports competitions, or when a patient arrives at a hospital emergency department with other possible stroke symptoms. Brain injury or diseaseĪ head injury, stroke or brain tumour can affect how your pupils react to light and cause dilated pupils. Sometimes, this sort of injury can occur during eye surgery, such as a complicated cataract surgery or a corneal transplant. 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)Ī serious, penetrating eye injury can damage your iris and cause the pupil of that eye to become dilated and irregular in shape. Here are some of the most common ones: Medications There's a wide variety of things that can cause dilated pupils. Anisocoria is benign and affects about 20 percent of the population. A large pupil that is completely unresponsive to light is called a 'fixed' dilated pupil.ĭilated pupils aren't the same as anisocoria, which is a common condition where both pupils react normally to light but differ in size by about a half millimetre or more.

Normal pupil size toddlers