Diplopia is of two types. Double vision when both eyes are open is called ‘binocular diplopia’ and double vision with one eye closed is ‘uniocular diplopia’. Causes of double vision differ in each.
There are two possible types of diplopia or double vision:
- Binocular Diplopia: This is the commonest type of diplopia. Double images of single objects are seen with both the eyes open. It classically disappears when one eye is closed. It occurs due to misalignment of the two eyes referred to as ‘squint’. Squint from early childhood usually does not cause double vision. Squint acquired later in life causes troublesome diplopia. It is usually due to paralysis of the eye muscles due to nerve palsies.
- Uniocular Diplopia: It is a much less common cause of double vision. Double images of single objects are seen even with one eye closed. It is caused due to structural defect in the eye’s optical system. The commonest cause of uniocular diplopia is cataract.