“A patient with diplopia is a challenge because of the complexity of the mechanisms involved in the control of eye movements. An early diagnosis is incredibly important in cases that may compromise the patient's life, which is why, when faced with sudden-onset diplopia, it is essential to see an ophthalmologist straight away”


Diplopia or double vision is the perception of two images of one single object. It happens because each eye perceives the object in a different point in the space, and the brain interprets it as if there were two objects.

Types and causes

Monocular diplopia: The double image is perceived with just one eye open. It is due to structural alterations to the eyeball, the most common being: 

  • Crystalline lens alterations: cataracts, crystalline lens subluxation.

  • Corneal abnormalities: keratoconus, corneal scarring or opacity.

  • Non-corrected refractive errors: astigmatism.

  • Macular pathologies: epiretinal membrane.

Binocular diplopia: This is most common type. It appears with both eyes open and disappears upon occluding one of them. It is caused by a lack of parallelism in both eyes because of an alteration to the oculomotor system. Although there are many diseases that may affect the alignment of the eyes, the most common are: 

  • Childhood strabismus compensated in adulthood

  • Oculomotor nerve palsy

  • Neurological diseases (myasthenia gravis)

  • Thyroid diseases

  • Brain tumours

  • Cranial and orbital trauma 

  • Eye surgery

  • High myopia

When the diplopia is binocular, the patient’s head occasionally adopts an abnormal position (torticollis) to compensate the double vision.

Depending on where the duplicated image appears, double vision may be horizontal (to the side), vertical (above or below) or oblique (diagonal) 


At the consultation, the ophthalmologist will ask for the patient’s medical history to obtain details on the way the diplopia appeared, its duration, if its constant or intermittent, if it is accompanied by other symptoms and if the patient suffers associated risk factors. In addition, they will undertake an examination of the anterior and posterior segment of the eye, a pupil reaction test and an ocular motility exam to determine the degree of deviation and the muscles causing it. In some cases, complementary tests will be required (analysis, neuroradiological study) to rule out a systemic compromise.


The prognosis will depend on the cause of the diplopia. Once diagnosed and treated, if the binocular diplopia persists, there are three therapeutic options.

  • Prisms: These are lenses that move the image to eliminate the double vision. They are indicated in small deviations.
  • Botulinum toxin: It is useful in certain cases of oculomotor palsy.
  • Extraocular muscle surgery: This may be required if the deviation is of a large magnitude. The objective will be to improve parallelism of the eyes, eliminate or reduce the diplopia, and correct the torticollis.

Dr. Idoia Rodríguez Maiztegui, ophthalmologist at the Barraquer Ophthalmology Center