Why am I seeing double and should I be worried?Saturday, June 1st, 2019, 2:51 pm
Seeing double can be a frightening and disorienting experience. It can be quite difficult to look at your phone or reach for your cup of coffee when you’re not sure which of the two you’re seeing is the real one! There can be a number of reasons why you are seeing double. Most experiences of double vision are temporary, lasting a few seconds to minutes, and are usually not a cause of worry. It can be precipitated by tiredness and lack of sleep or even drinking too much alcohol. Use of certain drugs can cause you to see double, such as opioids or benzodiazepines, or even a mild head injury such as a concussion. Double vision that is long lasting or keeps recurring should prompt an urgent visit to your eye doctor to make sure there is no serious underlying problem.
Double vision, or diplopia, occurs when you look at one object but see two images. The two images can appear side by side or on top of each other. You can tell whether it affects one or both of your eyes by simply covering one eye and checking if you still have double vision. If the double vision persists, only one eye is affected, known as monocular diplopia. If the double vision is only present when both eyes are open, it is binocular diplopia. Determining whether the double vision is monocular or binocular can help narrow down the possible causes as monocular points to a problem in the eye itself while binocular may be related to the brain and its related structures.
Monocular diplopia can occur when the light that enters your eye is being distorted on its way to your retina. Normally, light that enters the eye is focused onto the retina by the efforts of the cornea and lens which allow us to see one clear image of the world. This can be affected if you have a cataract, which is when the lens in your eye becomes clouded as you age. It can also be affected if you have an irregularly shaped cornea due to a condition called keratoconus. Additionally, astigmatism, which is when your eye shape is abnormal also prevents light from focusing on the retina and is another common cause of monocular diplopia. Even dry eyes can sometimes cause you to see double. These causes of double vision are not overtly worrisome and can be easily treated with lubricating eye drops, prescription glasses and/or surgical procedures depending on the condition.
Binocular diplopia, on the other hand, can occur due to a misalignment of the eyes that sends inconsistent visual information to the brain. The brain normally combines visual information from both eyes to create one single image of the world that we see. When the information from both eyes differs the brain is unable to produce one clear image and double vision occurs. The eyes are normally firmly attached to extraocular muscles which keep the eyes aligned and allow them to move in unison. The extraocular muscles are controlled by the cranial nerves which work together to allow smooth eye movements. Damage to the muscles or the nerves that control them can result in double vision. This can occur in a condition called myasthenia gravis where the eye muscles weaken with use due to weaker signals from the nerves and as the day progresses, double vision worsens. Similarly, double vision can be the first presenting symptom in people diagnosed with multiple sclerosis during which inflammation of the eye muscles causes them to weaken and may also result in pain when moving the eyes. In children, a common cause of binocular diplopia is strabismus, commonly known as being cross-eyed, where the eyes do not properly align with each other when looking at an object and may even appear to be looking in different directions if severe.
The most concerning causes of double vision are related to damage of the brain and include stroke, brain tumor, swelling or aneurysm. These can occur to damage of the eye muscles through different mechanisms such as blockage of blood vessels in the brain supplying them in a stroke or compression of the muscles by a brain tumor, swelling or aneurysm. In these cases, double vision would occur suddenly and the person may be seriously ill presenting with other symptoms such as muscle weakness or paralysis, numbness, headache, loss of balance and facial droop, depending on the condition. This would warrant an urgent visit to the ER to have the appropriate investigations and treatment.