stevensapple,
This is termed anisocoria. It is called simple anisocoria if it is a mild degree, which is found in about 20% of the population. A mild degree is considered .3 to .5 mm. So for some people this is normal, but this is something you would have to find out. Anisocoria can be caused by many diseases that affect the eye itself, a malfunction of nerves that control pupil size, or abnormalities in the part of the brain associated with eye function.
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