Diplopia is a symptom whereby a patient sees two images of one object.
It can either occur when one eye is covered (monocular diplopia), or only when both eyes are open (binocular diplopia).
In monocular diplopia, possible causes include uncorrected refractive errors, corneal disorders, cataracts and retinal disorders.
Binocular diplopia arises as a result of misalignment of the eyes.
The causes may be due to disorders affecting:
Nerve problemsNormal eye movements occur when the muscles attached to the eye are working properly and the nerves that stimulate these muscles are working normally. These nerves arise from within the brain, and if there is a problem involving one of these nerves, the eye will not be able to move fully in a particular direction, resulting in the experience of double vision from misalignment of the two eyes.
Some causes within the brain, such aneurysms and tumours, can be life-threatening. Patients may also have a droopy eyelid on the side of the problem, as well as abnormal eye position and a pupil that is larger on the affected side. If associated with headache or neck stiffness, it is important to seek medical treatment immediately.
Another important cause is a tumour arising from the back of the nose (nasopharyngeal cancer), which can compress on one or more of these nerves.
More commonly, "mini-strokes" can affect one or more of these nerves, and the risk factors associations are diabetes, hypertension, hyperlipidemia and smoking.
In these scenarios, the nerve problem tends to be temporary, with many cases recovering fully within four to six months. There is no specific treatment for such cases of double vision, although they serve as a reminder to control underlying risk factors.
Other more uncommon causes include various inflammations and infections.
Nerve-muscle junction diseasesMyasthenia gravis is an immune system disorder in which antibodies attack the nerve-muscle junction of different muscle groups in the body. If the eyes are affected, patients develop droopy lids and/or double vision. The characteristic feature is that symptoms are usually better upon waking up or after a period of rest and worsen throughout the day.
Myasthenia gravis can also affect the muscles of the rest of the body. Symptoms such as breathlessness, swallowing difficulties, weak voice, and arm and leg muscle weakness may indicate generalised myasthenia. When severe, myasthenia gravis can be life-threatening. Breathing may become increasingly difficult and swallowing problems may cause choking while eating and subsequently, lung infections.
Muscle disordersDiseases affecting the muscles that move the eye can lead to double vision. Thyroid eye disease is an important cause. The eye muscles become enlarged and stiff from the disease process and do not work normally.
Other symptoms include excessive sweating and weight loss despite an increased appetite, palpitations, anxiety, shaky hands and gradual prominence of one or both eyes. There may be a noticeable lump in the front of the neck as well (although it is possible to have thyroid eye disease without a thyroid lump present).
Inherited muscle diseases (myopathies) comprise different conditions that affect various groups of muscles in the body. Many of these myopathies affect the eye muscles as well. A muscle biopsy and/or blood test can help to confirm the diagnosis.
Eye socket (orbit) problemsOur eyes are enclosed in an eye socket which is a bony compartment in the skull called the orbit. Injuries that break the bones of the orbit can cause orbit tissues (such as fat or muscle) to be trapped in the fracture, leading to double vision.
Diseases within the orbit such as tumours and infections can also displace the eyeball and cause symptoms of diplopia.
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