why are my pupils different sizes

Having pupils of different sizes is known as anisocoria, and it can happen for several reasons. In many cases, it is physiological, meaning it is a natural variation where the difference in pupil size is usually less than 1 millimeter and does not indicate any disease. This type of anisocoria can be temporary or permanent and is found in about 20% of people without other symptoms. However, unequal pupil sizes can also result from other causes including physical trauma, infections, nerve inflammation, or certain medications. Sometimes it can be linked to underlying neurological or eye conditions such as Horner syndrome, where a smaller pupil is accompanied by drooping eyelid and reduced sweating on one side of the face, or from pressure on the nerves due to brain injury, tumors, or stroke. If the unequal pupil size appears suddenly, is accompanied by pain, vision changes, headaches, or other neurological symptoms, it is important to seek medical attention promptly. In children, differences in pupil size may be congenital or caused by nerve inflammation after viral infections, but may also point to more serious illnesses like neuroblastoma. Medications that accidentally get into the eye can also cause one pupil to be dilated. If one notices suddenly different pupil sizes or other symptoms such as pain, vision issues, or neurological symptoms, it is advisable to see a healthcare professional for evaluation to rule out serious causes.