Diplopia: why this double vision?

Definition: what is diplopia?

We speak of diplopia in a person who sees double. Abnormally, the eye distinguishes two images instead of one. “This double vision of a single object corresponds to a misalignment of our two visual axes”, explains Prof. Claude Speeg, president of the French Society of Ophthalmology.

A split vision can have many causes, more or less serious depending on their origin: trauma, neurological or vascular damage, etc.

Binocular diplopia or monocular diplopia: what does it mean?

There are different types of diplopia.

• We are talking regarding monocular diplopia when one eye sees double. It disappears as soon as this eye is hidden.
• Diplopia is binocular when it occurs with both eyes open. It disappears when one eye is closed or hidden. This type of diplopia results from the paralysis of one of the three cranial nerves which control the oculomotor muscles. If one of these nerves is damaged or compressed, the eyes are no longer in line, which explains the double vision.

Horizontal diplopia, vertical diplopia, oblique diplopia: what are the differences?

The vision can be duplicated in different ways, it all depends on the location of the problem.

• in case of horizontal diplopia, the two images are side by side. This anomaly may be related to a 6th cranial nerve palsy preventing the eye from turning outwards.
• We are talking regarding vertical diplopia when the two images are one above the other. This ocular disorder can be explained by a paralysis of the 4th cranial nerve, hampering the vertical movements of the eye.
• Diplopia can also be oblique. In this case, the images are skewed.

Double vision: how long does diplopia last?

In some people, diplopia occurs intermittently, without character of gravity. “It may be an intermittent exotropia or inconstant divergent strabismus”, explains Prof. Speeg. In this situation, the eye tends to deviate. “The patient compensates and catches up with the image thanks to his binocular vision”, says the ophthalmologist. The phenomenon occurs mainly in the event of visual fatigue in people whose strabismus has not been corrected. In this case, muscle rehabilitation is necessary.

The diplopia remains permanent “when it is linked to true ocular paralysis”, observe le Pr Speeg.

Is it serious to see double?

When a patient consults an ophthalmologist for diplopia, the doctor pays particular attention to certain warning signs:

Pre Claude Speeg, ophthalmologist: Sudden onset binocular diplopia, accompanied by headaches, pain or fever is a medical emergency. A neurological, vascular or orbital cause must be sought.

On the other hand, monocular diplopia is not an emergency. It is most often linked to cataracts or age-related macular degeneration (AMD) which require specific treatment.

Why am I seeing double? What cause?

There are many causes of double vision. To make a diagnosis, the doctor directs his questions according to the patient’s age and medical history. For young peopletraumatic causes are the most frequent. After 40 yearswe are looking for diabetes, high blood pressure or underlying thyroid disorders. In an elderly personthe priority is to exclude neurological or tumoral causes.

From main causes of diplopiawe find :

• trauma to the eye socket, linked for example to a car accident, to the practice of a sport, or to a punch. The double vision is explained by the lesion of a nerve or the fracture of the floor of the orbit, during the shock;
• a ruptured intracranial aneurysm: if the haemorrhage is located near an oculomotor nerve, it can compress it causing diplopia;
• a tumor in the orbit or an abscess related to an infectious disease can also compress a nerve;
• uncontrolled diabetes can be responsible for neurological damage to the eye, resulting in this double vision;
• arterial hypertension, at an advanced stage, damages the blood vessels and can cause diplopia by a phenomenon of compression;
• thyroid disorders are sometimes manifested by inflammation of the eyeball (exophthalmos) which can give double vision;
• multiple sclerosis (MS) leads to neurological damage. An ocular nerve may be affected.
• myasthenia gravis, an autoimmune muscle disease, also affects vision and can manifest as diplopia.

Can diplopia be drug-induced?

“In some patients taking neuroleptic treatment, the oculomotor balance is sometimes precarious. But this type of diplopia is very rare,” replies the Pre Speeg.

Assessment in case of diplopia: what are the necessary examinations?

It all starts with a orthoptic assessment in order to check the functioning of the eye muscles.

This report is accompanied by a Lancaster test. Specifically, the patient wears special glasses with a red lens on the right eye and a green lens on the left eye. He must stare at a point of light. The test makes it possible to observe the position of the gaze, to deduce where the oculomotor paralysis is located and to follow its evolution.

Of the imaging exams more advanced, such as a brain MRI, are requested when the doctor suspects a vascular or neurological origin (ruptured aneurysm, multiple sclerosis, etc.).

Diplopia rarely affects children

Double vision is mostly a problem of adults. In children, strabismus induces diplopia, but this is very quickly neutralized: this is amblyopia. A skill that we lose in adulthood.

How to cure diplopia?

First of all, the pathology that led to the double vision must be treated.

In absolute emergency situations, such as a ruptured aneurysm, surgery performed by a neurosurgeon is vital.

Apart from these extreme cases, diplopia resolves spontaneously in 90% of cases. There is therefore no need to rush”, observes the Pre Speeg.

How to correct diplopia?

Several solutions are possible to correct double vision.

• By artificially hiding the affected eye (for example by putting an opaque lens on a pair of glasses), the diplopia disappears.
• The wearing of glasses equipped with a special prism can, in some cases, suppress double vision.
• A local injection of botulinum toxin can, in some cases, allow the patient to recover normal vision more quickly.
• As a last resort, surgery is considered.