Double vision – also called diplopia – will make you see two separate images of a single object.
There are several different types of diplopia, and many different causes. Sometimes, double vision can be a symptom of an serious underlying disease or condition. For that reason, if you encounter double vision at any time, you should make an appointment with an eye expert straight away.
Symptoms of double vision
Double vision means that you simultaneously see two separate images of the same object. In some cases, double vision can be little more than a feint ‘ghost’ image, which is easily confused with blurred vision.
Double vision can be horizontal, where the images appear side by side; vertical, where the images appear one above the other; or diagonal, where the images are both vertically and horizontally displaced from one another.
Double vision makes it difficult to see objects at any distance, and can particularly affect your spatial awareness, and therefore your ability to drive. Children with double vision may frequently cover one eye, or they may tend to squint or turn their head in an unusual way to try to see properly.
Causes of double vision
In normal vision, the two separate images from each of your eyes are combined by the brain into a single image. Double vision occurs when the brain cannot combine the images from each of the eyes into a single image. This is usually because the images are not similar enough, because of problems with the muscles or nerves that control precisely where each eye is looking.
There are two main types of double vision – binocular and monocular.
Binocular diplopia is the most common type of double vision. It occurs when your eyes don’t align with each other as they normally would. Those with binocular double vision will find that covering either eye gets rid of the double image.
Binocular double vision is usually caused by a squint, but if it occurs suddenly, it could be a symptom of a much more serious medical condition. Diseases of the thyroid or arteries, along with diabetes, multiple sclerosis, stroke and a number of other serious conditions can cause double vision. It’s therefore essential to make an appointment with an eye specialist as soon as possible if you have double vision.
Monocular diplopia is double vision in one eye only, and is much less common than binocular diplopia. If you have monocular double vision, only covering the affected eye will make the double image disappear.
Monocular double vision is usually caused by an abnormality within the eye itself, such as a refractive error like astigmatism , or a rare type of cataract. It can also be caused by abnormalities of the iris, lens, or fluid within the eye, and even dry eye .
Treatment for double vision
If you suffer from double vision, your treatment will depend entirely on the type and cause of your diplopia. Treatment can be as simple as wearing an eye patch, or special glasses or contacts. Botox® injections or eyelid surgery may be used to correct a squint that causes double vision. Similarly, a cataract operation may be necessary if a cataract is the cause, or dry eye treatment may help if dry eye is the cause.