Aniso-: Unequal, unlike, or dissimilar. As in anisocoria, anisocytosis, and anisometropia. From the Greek anisos meaning unequal, from an-, not, + isos, equal. The opposite of aniso- is iso-.

Anisocytosis (pronounced “a-nuh-soe-sai-TOW-suhs”) describes red blood cells that vary in size. Sometimes, size variation in your red blood cells may signal an underlying medical issue. You may learn that your red blood cells are different sizes when you receive results from a blood test.

Anisocoria is a medical term for unequal pupil size. Normally our pupils are relatively the same size. While small differences in pupil size are normal and can even come and go (physiologic anisocoria), constant and significant differences in pupil sizes may be a sign of damage to the brain or the nerves that control the pupils.