What is Diplopia?

Diplopia is a symptom where 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).

Types of Diplopia

In monocular diplopia, possible causes include corneal disorders, cataracts and retinal disorders.

Binocular diplopia happens as a result of misalignment of the eyes. The causes may be due to disorders affecting 1) nerves, 2) muscles, 3) the nerve-muscle junction, or 4) bones surrounding the eye.

Binocular Diplopia — Nerve Problems

Normal eye movements happen 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 double vision from misalignment of the eyes.

Some causes can be life-threatening, for example, aneurysms and tumours within the brain. 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).

More common associations are diabetes, hypertension, hyperlipidaemia and smoking. In these cases, the nerve problem tends to be temporary, with many cases recovering fully within four to six months. Such cases are considered in a way to be "mini-strokes" to the affected nerve, and the associated conditions such as diabetes, hypertension and hyperlipidaemia as risk factors. There is no specific treatment for such cases of double vision though they serve as a reminder to control underlying risk factors.

Other causes of diplopia include various inflammations and infections.

Binocular Diplopia — Muscle Disorders

Diseases 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 that may be present 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.

Binocular Diplopia — Nerve-muscle Junction Diseases

Myasthenia 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 on waking up or after a period of rest and worsen throughout the day.

Myasthenia can also affect the rest of the body, and symptoms such as breathlessness, swallowing difficulties, a weak voice, and arm and leg muscle weakness may indicate generalised myasthenia. Severe myasthenia can be life-threatening, as breathing may become increasingly difficult, and swallowing problems may lead to choking while eating, lung infections and difficulty breathing.

Binocular Diplopia — Bone Problems

The eyes are enclosed in a bony compartment in the skull called the orbit. Injuries that break the bones of the orbit can cause orbit tissues (fat, muscle etc.) to be trapped in the fracture, leading to double vision. Diseases within the orbit, such as tumours and infections, can displace the eyeball and cause symptoms of diplopia.

Download the HealthHub app on Google Play or Apple Store to access more health and wellness advice at your fingertips.