A patient is seen reporting constant diplopia that persists when covering her right eye. What is the most likely etiology?

The presentation of constant diplopia that persists even when one eye is covered typically indicates a problem related to the ocular muscles or neuromuscular control rather than a refractive issue. In this context, uncorrected refractive error would not be the primary reason for the diplopia described, since refractive errors tend to cause diplopia only when both eyes are open and typically improve with occlusion of one eye.

In contrast, lateral rectus palsy, which affects the ability to abduct the eye, can lead to binocular diplopia that remains present regardless of which eye is covered, as the alignment is disrupted due to muscle weakness. Superior oblique palsy can also create diplopia due to vertical misalignment and will not resolve with eye cover. An aneurysm could result in diplopia if it compresses relevant cranial nerves, resulting in symptoms that persist with one eye covered as well.

Given these considerations, one can deduce that the underlying mechanisms of diplopia caused by muscle palsy or nerve compression are more aligned with the patient's symptoms than an uncorrected refractive error, which typically does not lead to persistent diplopia when one eye is covered.