Causes of Double Vision (Diplopia)

As the name suggests, double vision, also known as diplopia, occurs when a person sees two images of a single object. It has a significant impact on daily life since it can often affect day-to-day activities such as reading and driving. People with double vision will often experience problems with balance and movement as well.

Diplopia is not a disease but a symptom linked to a range of eye and brain problems or medication side effects. It is an ophthalmologic complaint that's found mainly in older patients. It can have both ocular and neurological causes.

Types of Double Vision

People with diplopia will see double images of a single object side by side or on top of each other. The condition can happen in both eyes (binocular diplopia) or just one (monocular diplopia). You can find out whether double vision is affecting both or only one of your eyes with a simple vision test: Close one eye and, if the image becomes normal, it means that just one eye has double vision.  

Causes of Monocular Diplopia

Monocular diplopia is less common, and it happens in only one eye. People often report that one of the images is clear and the other is blurry. In this case, double vision is often caused by an eye problem and not related to brain diseases.

Causes of monocular diplopia include:

• Cataracts: it is the most common cause of monocular double vision. The condition, clouding of the eye's lens, happens due to aging. Although it is not an emergency, the doctors may recommend surgery at some point
•  Eye muscle problems: Each eye has six muscles responsible for controlling eye movements. Problems in these extraocular muscles include weakness or paralysis that prevents one eye from moving in coordination with the other
• Dry eye: This happens when the eye produces fewer tears and it becomes less lubricated. It can happen for different reasons, including aging and staring at a computer for long periods of time. It can be solved by blinking, using artificial tears, or pinhole viewing
• Severe astigmatism: The most common symptoms of astigmatism are blurred or double vision. The condition changes the shape and curvature of the eye, which causes diplopia
• Keratoconus: This disease makes the cornea cone-shaped. It will cause many symptoms, including double vision, sensitivity to light, and blurry vision
• Pterygium: Also known as surfer's eye, it happens when the membrane that covers the white part of the eye overgrows and covers part of the cornea. Double vision is one of the symptoms of this condition

Causes of Binocular Diplopia

Binocular diplopia occurs when the eyes are not aligned. People with binocular diplopia often report that images in both eyes are clear and one of them will disappear when they cover one eye. It can be caused by a range of diseases, and some of them can involve the brain nerves.

Causes of binocular diplopia include:

• Diabetes: Among other things, diabetes can cause nerve damage, including to the eye, which causes double vision. People who have diabetes are also more likely to have cataracts
• Guillain-Barre syndrome: This condition can cause muscle weakening, and the first symptoms are often vision-related like diplopia
• Myasthenia gravis: This is an autoimmune disease, in which the immune system attacks healthy cells. It typically strikes muscles in the face first. Muscles that control the eyelids and eye movements are usually affected early on in this disease. Double and blurry vision are some of the symptoms
• Multiple sclerosis: This disease affects the nervous system and can damage nerves that control eye movement. The weakening of these nerves will also cause double vision
• Graves' disease: Extreme cases of Graves' disease can swell the eye muscle, which may put extreme pressure on the optic nerve, leading to double vision or vision loss
• Strabismus: This condition, also known as crossed eyes, can cause double vision, but not always. If strabismus has been present since childhood, the misalignment may suddenly become noticeable, but there is usually no double vision. Cases of misalignment suddenly occurring in adulthood is usually accompanied by double vision

A Word From Verywell

The eyes are among the most sensitive parts of the body, and people should not ignore sudden vision changes. Although some cases of double vision can disappear in a few seconds, it becomes a red flag when it persists for long periods or happens multiple times. The cause of diplopia can be as simple as dry eyes, but double vision can also be a sign of neurological damage.

Schedule a visit with an optometrist or ophthalmologist when you notice that you have double vision. Discovering a disease early makes a whole world of difference in treatment and the outlook of the disease.