Diplopia

Diplopia, or double vision, is the subjective perception of two images of a single object. It is a symptom rather than a disease and can have a variety of ocular or neurologic causes. Diplopia is classified as monocular, which persists when the affected eye is covered, and binocular, which disappears when either eye is closed. Monocular diplopia usually points to ocular surface or lens problems such as refractive error, cataract, or corneal irregularity; binocular diplopia typically results from misalignment of the visual axes due to extraocular muscle weakness, cranial nerve palsies, or orbital disease.

Common binocular etiologies include cranial nerve III, IV, or VI palsies, thyroid-associated ophthalmopathy, myasthenia gravis, strabismus, and orbital lesions. Vascular risk factors can contribute to ischemic nerve palsies. Less often, diplopia reflects central nervous system lesions such as brainstem or cortical strokes, demyelinating disease, or mass lesions. Ocular motility abnormalities may produce horizontal, vertical, or oblique diplopia, which can worsen at certain gaze positions or with prism compensation.

Evaluation relies on history and comprehensive eye examination. Key steps include distinguishing monocular from binocular diplopia, assessing visual acuity and refraction, performing a cover test and motility assessment, and examining pupils and the optic nerve. When indicated, imaging (MRI or CT), vascular and autoimmune workups, or neuro-ophthalmology consultation may be pursued.

Management targets the underlying cause. Refractive correction or cataract surgery can relieve monocular diplopia; prism glasses or surgical correction may improve binocular diplopia due to strabismus. Acute, new diplopia with headaches, neck stiffness, fever, or focal neurological signs is an emergency until serious pathology is excluded.