What is diplopia (double vision)?

Diplopia means seeing two images of a single object. The images may appear side by side, one above the other, or diagonally separated. It can affect one eye (monocular diplopia) or both eyes together (binocular diplopia). In binocular diplopia the double vision disappears when either eye is covered.

How the visual system works

For comfortable single vision, both eyes need to be aligned and move together, and the brain must correctly "merge" the two images into one. Diplopia usually occurs when something in this system is disrupted, for example:

• Eye misalignment (strabismus) due to weakness or restriction of the eye muscles, or problems with the nerves that control them (for example after stroke, head trauma, diabetes, or nerve palsy).
• Optical problems in one eye, such as irregular cornea, cataract, or uncorrected refractive error, which can cause ghosting or doubling even when the other eye is covered (monocular diplopia).

When to seek medical attention

Double vision has many possible causes, some of which need prompt medical attention. An eye-care professional can assess the cause and discuss appropriate options. Exercises may be considered for some diagnoses, but they are not a general treatment for all double vision.

References

1. Jain, S. (2022). Diplopia: Diagnosis and management. Clinical Medicine, 22(2), 104-106.
2. Glisson, C. C. (2019). Approach to diplopia. CONTINUUM: Lifelong Learning in Neurology, 25(5), 1362-1375.