What Does It Mean When One Pupil is Bigger than the Other?

When one pupil is bigger than the other, called anisocoria, it can indicate various conditions ranging from harmless to serious. Normal pupils should be equal in size, typically 2-4mm in bright light and 4-8mm in darkness. Anisocoria affects about 20% of the population and can be physiological (natural variation under 1mm difference) or pathological. Common causes include eye injuries, certain medications, neurological conditions like Horner's syndrome, or brain issues affecting the third cranial nerve. Sudden onset anisocoria, especially with symptoms like severe headache, vision changes, or drooping eyelid, requires immediate medical evaluation as it may signal stroke, aneurysm, or increased brain pressure.

Related Questions

• When should I see a doctor for unequal pupils?

• What medications can cause pupils to be different sizes?

• Can anisocoria be a sign of a stroke?

• Is it normal for pupils to be slightly different sizes?

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