Causes and differential diagnosis of diplopia

1. Big picture

Diplopia = double vision. In neurology, diplopia is important because it often means that the two eyes are not aligned, usually due to a lesion affecting the ocular motor system: cranial nerves III, IV, VI, their nuclei/fascicles in the brainstem, the neuromuscular junction, extraocular muscles, or the orbit. The first exam question is always: Is it monocular or binocular?

The most important rule:

Binocular diplopia disappears when either eye is closed. This usually means ocular misalignment and is neurologically important. Monocular diplopia persists when the other eye is closed and is usually ophthalmological, such as refractive error, corneal disease, cataract, or lens problems.