Sixth nerve palsy

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Sixth nerve palsy (abducens nerve palsy) is a problem with the nerve that controls the eye’s outer movement. The lateral rectus muscle turns the eye outward. When the nerve doesn’t work, the eye drifts inward, causing horizontal double vision (diplopia) that’s worse when looking at distant objects. People may turn their head to help reduce the double vision.

Who gets it
- Usually affects one eye, but can involve both.
- In children, diplopia may be suppressed, so they might not notice double vision, which can risk developing amblyopia (lazy eye) if not watched.

Causes
- Adults: brain problems (injury, tumors, increased intracranial pressure), inflammation, or vascular issues.
- Children: trauma, brain tumors, infections, or sometimes no clear cause (idiopathic).
- The sixth nerve is long and near areas where problems like rising pressure, inflammation, or tumors can affect it.

Diagnosis
- Sudden onset double vision with the eye not moving outward well.
- The misalignment is usually worse when the person looks to the side or at distance.
- Doctors examine eye movements and may image the brain if needed to find the cause.

Treatment and management
- First, treat the underlying cause if possible.
- In children, the goal is to protect normal visual development; observe for about 6 months because some cases recover spontaneously.
- Prisms (Fresnel prisms) can be added to glasses to reduce diplopia. If prisms aren’t enough, one eye may be covered temporarily.
- Botulinum toxin can be injected into the inward-pulling medial rectus to lessen its force and help recovery, while also helping doctors assess remaining eye movement.
- If there is no recovery after about 6 months, surgery is considered.
- If some function remains, surgeons may weaken the medial rectus and/or strengthen the lateral rectus.
- In severe or complete paralysis, more advanced procedures like vertical muscle transpositions may be used to help the eye turn outward.
- For both eyes affected, the same principles apply to each eye.