1. Is it monocular or binocular?

Monocular diplopia occurs only when one eye is open

- the problem is in the eye itself!

Binocular diplopia occurs when BOTH eyes are open (ie. cover either eye and diplopia resolves)

- problem is due to misalignment of the visual axis

2. Ask which direction is the double vision worse?

- diplopia is usually worse when the patient is attempting to look in the direction of the malfunctioning occular muscle

3. Consider the cranial nerves involved in vision when putting together your differential

- Cranial Nerve IV (Trochlear) rotates eye inferiorly and intorsion (Superior Oblique)

Palsy results in "nasal upshot"

Trauma is a common cause (even benign)

- Cranial Nerve VI (Abducens) responsible for lateral movement (lateral rectus)

Palsy results in an eye that appears "crossed"

Consider conditions that increase ICP

- Cranial Nerve III (Oculomotor) controls "all other ocular muscles" and is involved in eyelid elevation and pupil constriction

Palsy results in an eye that is "down and out"

Consider vascular causes (typically pupil sparing) and aneurysms