Ocular myasthenia: drooping eyelids and double vision explained

Myasthenia gravis is, according to the NHS, a rare long-term condition that causes muscle weakness. It most commonly affects the muscles that control the eyes and eyelids, facial expressions, chewing, swallowing and speaking. It is an autoimmune condition: the immune system mistakenly attacks the communication system between nerves and muscles, so the muscles are weak and tire easily.

The University Hospitals Sussex leaflet, written by its orthoptic department, explains that in myasthenia gravis the body produces antibodies that block the messages passing from nerve endings to muscles, so the muscles do not contract as well. The weakness gets worse the more a muscle is used. In ocular myasthenia the weakness stays within the muscles that lift the eyelids and move the eyes.

The Sussex leaflet says myasthenia gravis affects about one person in every 10,000 in the UK, and can develop at any age, though it is more common in women under 40 and in men over 60.

The NHS lists droopy eyelids, affecting one or both eyes, and double vision among the commonest features, with facial expression changes. The Sussex leaflet adds that a person may find symptoms worse when tired or after using an affected muscle for longer or harder, and that hot weather, infections, stress or menstrual periods may trigger symptoms.

The key clue is variability. The Sussex leaflet describes double vision or droopy eyelids caused by muscle weakness that gets worse when you are tired, and comes and goes or gets better and worse, as raising the possibility of myasthenia. The NHS also notes that symptoms tend to get worse when tired and are often better the next morning after sleep.

• Eyelid droop (ptosis) that becomes more obvious late in the day or when looking up for a long time.

• Double vision that comes and goes, and may disappear when one eyelid droops enough to cover the eye.

• Weakness of facial expression in some people.

• Symptoms that fluctuate from hour to hour or day to day.

Ocular myasthenia is confined to the eye muscles, but myasthenia gravis in general can affect breathing and swallowing. The NHS says to call 999 for an ambulance immediately if you have worsening severe breathing or swallowing difficulties, because you may need emergency treatment in hospital. New speech slurring, chewing or swallowing problems, or weakness of the neck or limbs in someone known to have ocular myasthenia suggests that it may be spreading and should be reported promptly to the neurology team or GP.

Sudden double vision or a drooping eyelid, especially with severe headache, a change in the pupil or new weakness or numbness elsewhere, can have other causes and needs prompt medical assessment, through NHS 111 or an emergency department if it is severe or sudden.

The NHS says myasthenia gravis can be difficult to diagnose and you may need several tests. A GP may notice the pattern, or an optician or orthoptist may be the first to notice double vision or eyelid droop. If they suspect a problem with the brain or nerves they may refer you to a specialist for tests.

The NHS describes the main test as a blood test for the antibody that stops signals passing between the nerves and muscles. A high level usually means myasthenia gravis, but not everyone has a high level, particularly if only the eye muscles are affected, and the test may be repeated later if the result is normal but symptoms continue or worsen. It also describes electrical nerve and muscle tests (electromyography), CT or MRI scans of the chest to check the thymus gland for enlargement or a thymoma, sometimes an MRI brain scan to make sure symptoms are not caused by a problem in the brain, and, rarely, the edrophonium test, which is only done in hospital because of risks such as a slow heartbeat and breathing problems.

The Sussex leaflet notes that the ophthalmologist arranges blood tests, and that a chest scan may be needed to check the thymus gland or for other problems that give similar symptoms.

There are two parts: treating the myasthenia itself and managing the double vision. The Sussex leaflet says the usual treatment is a type of medicine called an acetylcholinesterase inhibitor, which improves the connections between nerve endings and muscles. If there is a tumour of the thymus gland, an operation to remove it may be offered, sometimes followed by medical treatment. The NHS adds that treatment aims to keep symptoms under control by avoiding triggers such as tiredness and stress, using medicine to improve muscle weakness and, for some, surgery to remove the thymus gland. Before treatment you are referred to a neurologist or endocrinologist.

For the eyes, the Sussex leaflet explains that symptoms differ for everyone and change over time, which can make them hard to relieve. Double vision may be relieved because the drooping eyelid covers the eye, by a prism in your glasses to join up the images, by an eye patch, which may work better for longer-term relief than a prism, or, if you are unable to open an eye, by taping the eyelid open for a time with protective drops or gel for the eye surface. It cautions that prisms may not always work well because symptoms vary.

The NHS says that for most people with myasthenia gravis the weakness spreads to other parts of the body over a few weeks, months or years, but that for some only the eyes are affected, and that if you have had eye symptoms for 2 years or more, it is unusual for other areas to be affected later on. It describes the condition as long term with phases of improvement and worsening, and it says flare-ups are common, with remission sometimes occurring though permanent remission is rare. It notes that myasthenia gravis does not have a significant impact on life expectancy for most people.

The Sussex leaflet adds that there is no cure, but that people often find their symptoms are better once on medicine or after thymus surgery, may have long periods without worsening, and may go into long-lasting remission.

On the NHS the route is usually GP or optician, then ophthalmology or orthoptics, neurology and blood tests, chest imaging and treatment planning. Clinical teams pass information about people with myasthenia gravis to the National Congenital Anomaly and Rare Disease Registration Service, from which you can opt out at any time.

A private neuro-ophthalmology or neurology appointment may offer quicker testing, but treatment decisions and monitoring should be shared with your NHS team. Ask who will manage prism glasses, medicine adjustments and any thymus assessment.