Ocular muscle paralysis

Ocular muscle paralysis is a condition in which one or more of the six extraocular muscles that move the eye do not function properly. These muscles normally enable your eye to look in all directions: to the left, right, up, down and diagonally. In the case of paralysis, one or more of these muscles do not respond, or respond inadequately, to signals from the brain.

The cause may lie in the muscle itself, in the nerve that controls the muscle, or in the part of the brain that regulates eye movements. Possible causes include a stroke, a brain tumour, multiple sclerosis, diabetes, head or eye trauma, an infection, or inflammation of the optic nerve. Sometimes the cause cannot be immediately identified.

The symptoms depend on which muscle or nerve is affected. Common symptoms include double vision (diplopia), as the eyes no longer move in sync and send two different images to the brain. The eye may also turn inwards or outwards (strabismus), the eye may not open fully (ptosis due to paralysis of the eyelid muscle), or the field of vision may be restricted in a particular direction. Some people turn their head to compensate for the double vision.

Eye muscle paralysis can occur suddenly or gradually, and may be temporary or permanent. In children, untreated eye muscle paralysis can lead to a lazy eye (amblyopia), as the brain begins to suppress the image from the affected eye.

Ocular muscle paralysis is a medical condition that must always be investigated by an ophthalmologist or neurologist. The doctor will test eye movements, check pupil responses and often carry out additional tests such as an MRI or CT scan, blood tests or a neurological examination to determine the cause.

Treatment depends on the underlying cause. Sometimes the paralysis resolves on its own, for example following a viral infection or minor nerve damage. In other cases, treatment of the underlying condition is required, such as managing diabetes or treating an inflammation. In cases of permanent paralysis, prism lenses in spectacles can reduce double vision, or an ophthalmologist may consider surgery to correct the eye alignment.

If you suddenly experience double vision, a squint, a drooping eyelid or difficulty moving your eye, have it assessed immediately by your GP or ophthalmologist. Particularly if these symptoms occur suddenly, they may be a sign of a serious condition such as a stroke or a brain tumour, and prompt diagnosis is crucial.

If you wear contact lenses and suffer from eye muscle paralysis, discuss with your ophthalmologist or optician whether and how you can continue to use your lenses safely. Sometimes, the paralysis can cause your vision to be too variable or too limited to wear lenses comfortably.