Eye Nerve Palsies (3rd, 4th and 6th Nerve)

Six small muscles move each eye. They are controlled by three nerves from the brain. A palsy means one of these nerves is not working properly, so the eyes no longer move together [1].

• 3rd nerve (oculomotor): controls most eye movements, lifts the eyelid and makes the pupil smaller. A palsy can cause a droopy eyelid, an eye that turns down and out, and sometimes a large pupil.
• 4th nerve (trochlear): helps the eye look down and inwards, for example when reading or walking down stairs. People may tilt their head to avoid double vision.
• 6th nerve (abducens): turns the eye outwards, towards the ear. Double vision is worse when looking to one side or into the distance.

Common causes include [1][3]:

• Diabetes, high blood pressure and high cholesterol, which can block the tiny blood vessels feeding the nerve (microvascular palsy), mostly in people over 50
• Head injury
• Raised pressure inside the head
• An aneurysm (a bulging blood vessel in the brain), a stroke, a tumour, or infection or inflammation, which are less common but serious

The main symptom is sudden double vision (diplopia): seeing two of everything, side by side or one above the other [1]. It usually goes away when you cover one eye.

You may also notice a droopy eyelid, an eye that turns in or out, a large pupil, or pain around the eye. An eye doctor will check your eye movements and pupils, and you may need blood tests and a brain scan [3].

Some palsies are caused by a problem in the brain, such as an aneurysm or stroke, that needs treatment straight away [2][3].

Treatment depends on the cause [1][3]:

• Treat the cause, for example controlling blood sugar, blood pressure and cholesterol.
• Covering one eye with a patch, or a sticker on your glasses, stops the double vision while the nerve recovers.
• Prisms on glasses can help bring the two images together.
• Many microvascular palsies get better by themselves, usually within about 3 months [3].
• If the double vision does not go away, eye muscle surgery or injections may help.

Do not drive while you have double vision.

Where to get help in Brunei

For double vision without any of the emergency signs above, you can walk in to any Community Eye Clinic at your health centre. No referral is needed.