Diplopia is the medical term for seeing one object as two objects; it is also known as double vision. There are two different kinds of diplopia: monocular and binocular. Monocular diplopia occurs when a patient experiences double vision (or more likely distortion) even when one eye is closed. Binocular diplopia occurs when a patient experiences double vision only when both eyes are open; if one eye is covered, the other eye will see a single image.
The most common causes of diplopia are misalignment of the eyes (strabismus), damage to the nerves that control the eye muscles, astigmatism, keratoconus, dry eyes, retina damage, diabetes, myasthenia gravis (a neuromuscular illness), Graves’ disease (autoimmune hyperthyroidism) and trauma.
The treatment of diplopia depends on the cause. For example, monocular diplopia caused by astigmatism can be treated with toric contact lenses. Other forms of diplopia may be treated with a new glasses prescription, prisms, vision therapy or eye muscle (strabismus) surgery. Diplopia caused by medical or neurological disease may be treated with botulinum toxin (Botox ™) injections, surgery or treatment of the underlying disease.
Because the causes and treatments of diplopia are so numerous, it is crucial that patients experiencing double vision undergo a comprehensive eye exam (including a review of medical history) with their eye doctor. Identifying diplopia in children is more difficult than in adults because children rarely complain of double vision either because they don’t think double vision is abnormal or their developing brains suppress vision from one eye. If eye misalignment is noted or if a vision screening suggests poor vision in one or both eyes, a comprehensive exam is warranted to prevent permanent vision loss.