What would cause double vision when looking to the side both ways?

VADouble to the side: Horizontal diplopia ( images look doubled side to side not on top of one another) when looking to extreme side most likely a weakness of lateral rectus muscles, born with or acquired types. Sometimes a neurologic condition ms or uncontrolled diabetes or blood pressure . If recent onset definite see an md eye doc for help.

6th nerve lesions: The lateral rectus muscle moves the eye to the side. When this is not working well, you will see double when trying to look to the side. Many neurological disorders can affect the 6th nerve. A thorough neurological evaluation would be appropriate.