Ocular myasthenia

What is Ocular myasthenia?

Ocular myasthenia is a form of myasthenia in which the extra-ocular muscles, the muscles that control the eyes and eyelids, are easily fatigued and weakened.

What are the muscles that control the eyes?

Symptoms

If you have ocular myasthenia you are likely to have experienced double vision (diplopia) or drooping eyelids (ptosis). Your eyes will not move together in balanced alignment, causing you to see 'double' images. One or both of your eyelids may also droop to cover all or part of the eye pupil, thus obstructing vision.

Eye weakness will often change from day-to-day and during the day. Problems with eyes are often worse at the end of the day or after the eyes have been used for a prolonged period of time. You may find that your eye problems are temporarily improved if you rest your eyes by closing them for several minutes when your symptoms are troubling you.

If you have ocular myasthenia, you will NOT have difficulty with swallowing, speaking or breathing, nor will you experience any weakness of your arms and legs.

Diagnosis

Ocular myasthenia is diagnosed in the same way as other myasthenias. If your symptoms only affect the muscles around your eyes for longer than two years, then your condition is unlikely to progress to other muscles.

Many people with ocular myasthenia first consult an optician about their eye problem. Optometrists are frequently the first medical professionals to suspect ocular myasthenia and will refer you to a neurologist for further tests.

You will have a blood test to detect the anti-acetylcholine receptor (AChR) antibodies, which are positive in around 50% of people with ocular myasthenia.

If the test comes back negative, you may receive a very sensitive electrical test (Electromyography) on your facial muscles.

In some cases, people will be given an injection to test out the body's response to a drug called Tensilon®.

Treatments

Pyridostigmine

As with most forms of myasthenia, pyridostigmine is usually the first-line treatment. For many people, pyridostigmine alone is able to control their symptoms.

Side affects may include stomach cramps, digestive problems and an urgent need to urinate.

Immunosuppressive drugs

If pyridostigmine alone is not enough, immunosuppressive drugs may be introduced.

The steroid prednisolone is often used. Dosage may have to be built up high before a lower maintenance level is found. Benefits of the drug will typically kick in after 2-3 months.

Side affects may include weight gain, hypertension, glaucoma, cataract and / or osteoporosis.

Ptosis Props

These are useful if drug treatments are not fully successful. Before they are prescribed to you, it would be helpful for you to be shown samples of the different types of prop available. Ptosis props are designed to literally 'prop' your eye open.

Lundie Loops

You may be offered a device called the Lundie Loop, which is a circle of stainless steel wire. They are designed so you can look through the middle of the loop. The upper part of the loop, which bears lightly on the eyelid, is fitted with a short piece of silicone rubber tubing.

Traditional bar ptosis props

These can be fitted to most glasses. The length and size of them will be determined by the optometrist. Rubber tubing can also be used to cushion the bar.

Eye prisms

A prism is a wedge-shaped piece of glass or plastic that bends the light that shines through it. Fresnel prisms can be attached to your glasses and are an effective way of treating double vision.

Fresnel prisms are thin, see through sheets of plastic. One side sticks to the lens of your glasses and the other side has special grooves in it that changes the way light enters your eye.

You may need to wear prisms for several months. The strength can be adjusted to suit your eyes. If the Fresnel prisms are successful, you can have glasses made with prisms built in.

Drugs that can make myasthenia worse

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