Double Vision

Depending on whether the patient sees double from one eye or both, double vision is divided into:

• Monocular double vision, where the problem exists in only one eye. Closing this eye can make the problem go away temporarily.
• Binocular double vision, where the problem exists when looking through both eyes. Closing either eye makes the problem go away temporarily—some people wear an eye patch for relief.

This difference is significant, as it could help the doctor diagnose the underlying cause for the patient's double vision.

As the name suggests, seeing two images instead of one is the main symptom of double vision or diplopia. However, some patients may also experience other problems like

• Headache
• Nausea
• Eye pain
• Pain around the eyes
• Pain while moving the eyes
• Drooping eyelids

You should see a doctor immediately if you have double vision along with any of the following symptoms:

• Severe eye pain or feeling of pressure behind the eye
• Shingles rash on the forehead, eyelids, nose
• Severe headache

The eyeball comprises the retina at the back; the cornea, iris, pupil, lens and conjunctiva in the front; and the eye muscles (extraocular muscles) that keep the eye in its place.

We see things when light reflected from an object enters the eye through the lens, forms an image on the retina and the brain processes this image. A problem with any of the parts of our eye or a misstep in any of these stages of seeing may cause double vision.

Depending on the type of double vision, the causes can be:

Monocular double vision:

• Dry eyes: People who spend several hours in front of a computer may develop dry eyes because of digital eye strain. People with diabetes also tend to have dry eyes. One of the symptoms of dry eyes is seeing double. Usually, this condition improves when you rest the eyes adequately and use eye drops containing hydroxypropyl methylcellulose (artificial tears) to lubricate them. 
• Cornea problems: The cornea focuses light onto the lens of the eye. Any condition that affects the “roundness” of the cornea interferes with proper vision. Some of the cornea problems that can cause double vision are:  
  • Astigmatism: Abnormal curvature of the cornea. This can be addressed by using the right prescription glasses with cylindrical lenses or through surgery.
  • Keratoconus: The cornea becomes thin and bulges into a kind of cone shape. This distorts the vision, causing blurry vision or double vision.
  • Pterygium: This is a problem of the conjunctiva in the corners of the eyes. However, it can make the mucus covering of the eyes thicker and affect the cornea’s ability to focus the light into the eye.
• Cataract: Cataracts cover the lens, making it difficult for the eye to focus the image properly. This can sometimes lead to double vision. Double vision may also occur if the eye lens becomes detached for any reason.
• Macular degeneration: The macula is the central portion of the retina. It can deteriorate with age (age-related macular degeneration) or due to other risk factors like a family history of macular degeneration. Seeing a solar eclipse improperly can also cause irreversible damage to the macula. (Read more: How to see a solar eclipse safely)

Binocular double vision:

• Misaligned eyes: Strabismus (cross-eyes) or a lazy eye (amblyopia) are both conditions arising from an alignment problem—the eyes don’t work together, resulting in vision problems. (Read more: Vision problems in babies)
• Nerve and muscle damage: Any condition that causes damage to the optical nerve or the muscles of the eyes can result in double vision. These conditions include:
  • Autoimmune diseases like myasthenia gravis, Grave’s disease and Guillain Barre syndrome
  • Multiple sclerosis, a condition in which the protective covering around the nerves starts to wear away
  • A brain tumour or aneurysm may press on the optical nerve and cause double vision in some patients. An aneurysm is a bulge in the blood vessels.
  • Diabetes can affect the nerves and cause vision problems
• Double vision and drooping eyelids may be a sign of stroke. Some patients may develop double vision after a stroke.
• A head injury may also result in double vision in some cases.

Other causes of double vision:

• Wernicke encephalopathy: Caused by a vitamin B1 deficiency, one of the first symptoms of Wernicke encephalopathy is double vision.
• Infections like ophthalmic shingles (herpes zoster) which can cause inflammation in the cornea or retina.
• Alcohol intoxication may cause double vision until the effects wear off.
• A concussion, head injury or black eye can also cause double vision for a limited time.

Double vision is a symptom rather than a disease—it can appear suddenly or develop over time. In some cases, you can't prevent double vision. For example,  head trauma or stroke are events that no one can anticipate.

The best thing you can do in these cases is to not ignore signs of double vision. Even if the cause is a progressive disease like Guillain-Barre syndrome, it is better to heed the signs and try to delay further eye problems.

In some conditions, there are a few things you can do to prevent double vision. These include:

• Eye exercises: Here's one you can start with: take an intricate picture and hold it at arm's length. Now try focusing on the details. If the image splits in two, try to merge the segments without squinting your eyes. Do this for at least 10 minutes. This and other eye exercises can help to strengthen the eye muscles and improve focus.
• Eat healthily: Take care of your diet. Include vitamin B-rich foods in your meals, especially if you have had bariatric surgery.
• Get your eyes checked regularly: Keep your appointments with the ophthalmologist, to make sure you don't need glasses. Or if you already wear glasses, your number is updated. You should also replace your glasses periodically: scratched, bent or otherwise damaged glasses can also cause double vision.
• Take good care of your overall health: If you have diabetes, try to ensure that your blood sugar levels don't fluctuate too much. If you have a condition like Graves' disease, make sure you follow the care protocol for hyperthyroidism to control symptoms like vertical double vision.

Double vision is a symptom rather than a condition. Patients would be able to feel they are having vision problems if they see double out of one or both eyes. Sometimes, this problem goes away after resting the eyes. But if it recurs, you should see a doctor. You should also see a doctor if the symptom occurs suddenly.

Another thing, sometimes double vision is only noticed when you try to see from the corner of your eyes or well above or below your line of vision. It is a good idea to do eye exercises and look up, down and side-by-side daily to know if and when the problem of double vision arises.

To diagnose double vision,

• The doctor will start by examining whether the problem is in one or both the eyes. He or she may also ask you if you’re having vertical double vision (which could be a sign of Grave’s disease), horizontal or side by side double vision or both.
• He or she will ask about your medical history as well as any family history of diabetes, multiple sclerosis, myasthenia gravis (which affects the muscles), Guillain Barre syndrome (which affects the nerves), macular degeneration (which affects the retina), etc.
• Depending on the doctor’s assessment, he or she may order some tests such as:
  • Eye exam: This exam can help to diagnose issues like problems with the cornea (astigmatism, keratoconus), eye lens problems (detached lens, cataract), conjunctiva problems (pterygium), retina problems (macular degeneration). Your eye doctor may dilate your eyes for this exam.
  • Blood test: Blood sugar (glucose) test to check for diabetes and thyroid-stimulating hormone test to check for hyperthyroidism (the body can produce too much thyroid hormone in Graves' disease) may be necessary to determine the underlying cause of the problem.
  • Head scans: Magnetic resonance imaging or MRI scan of the brain to check for any bleeds, brain aneurysms or tumours in the brain. Computed tomography or CT scan of the head for signs of injury or bleeding.

Depending on the cause, the treatment of double vision may involve

• Using corrective glasses: Wearing the right prescription spectacles can help improve some conditions like astigmatism and strabismus.
• Using an eye patch: Wearing an eye patch will help to improve symptoms in the case of binocular double vision.
• Using eye drops: This is particularly helpful in the case of double vision linked to dry eyes.
• Giving rest to the eyes: Double vision due to conditions like dry eye syndrome and even myasthenia gravis may improve temporarily by giving adequate rest to the eyes.
• Eye exercises: Exercises that strengthen the eye muscles and improve alignment can help to ease double vision.
• Surgery: Procedures like cataract surgery, radial keratotomy or laser eye surgery for astigmatism can treat the respective problems. Once the problem is gone, the symptom—double vision, in this case—will also improve.
• Medication: Medicines may be prescribed for lifelong management of conditions like diabetes, Grave’s disease, myasthenia gravis and multiple sclerosis.
• Botox injections: Botox injections may be given to relax the muscles of the stronger eye in patients with conditions like a lazy eye. This would improve the patient’s chances of using the weak eye to focus. However, this is a temporary fix and patients will need to get botox injections at regular intervals.
• Diet: Wernicke’s disease occurs because of thiamine (vitamin B1) deficiency, usually after bariatric surgery or in people with eating disorders. In addition to vitamin B injections and medicines, the patient may be advised to eat well. Thiamine-rich foods include long-grain white rice, black beans and kale.
• Other therapies: For some conditions, like head or face trauma, different therapies like applying an ice pack, stitches, etc., may be used to treat bruises, fractures, cuts, black eyes, concussion or pain.