(sin-nee’-kia)
Pupil size determines the amount of light entering the eye. The size of the pupil changes to allowthe best vision under different light conditions. Normal pupil diameter is 3-4 millimeters, but this varies from person to person and with age. Anisocoria means that the two pupils are unequal in size. Testing is needed to determine whether or not this is abnormal for a particular individual. Many people have slight, totally normal differences in pupil size. Occasionally people have large differences in pupil diameter that are normal.
Where testing indicates that the difference in pupil size is abnormal, observation is used to identify which is the abnormal eye. If the difference is greatest in darkness, the smaller pupil is the abnormal eye. If the difference is greatest in light, the larger pupil is the abnormal one.
Neurological examination may be needed to determine the cause of the abnormal difference in pupil sizes, as damage to the optic nerves can create unequal pupils. Injury to the eye, certain eye drops or ointments, can also cause unequal pupils. Skin patches used to control motion sickness can temporarily cause a larger pupil on the side the patch was applied
