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Person with double vision trying to unlock something with a key

Illustrated by Gentry Griffith

What Are Prism Glasses and Can They Help People With Myasthenia Gravis?

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By Editorial Team

2 min read

Weakness of the muscles that control eye movement often causes the first symptoms of myasthenia gravis (MG). While there are therapies available to treat MG, prism glasses are not usually as helpful as other treatment options.1,2

Overall, 2 out of 3 people with MG experience eye symptoms. These symptoms include:1,2

Seeing double

Double vision (or diplopia) means seeing 2 images instead of 1. Usually, the eyes move together. The brain combines the images seen by each eye into a single image.3

Double vision happens in some people with MG due to weakness of the muscles that control eye movement. This weakness interferes with the usual process of coordinated eye movement. In people with MG, the eyes may be unable to align correctly. This causes light to enter each eye differently. The brain is then unable to combine the 2 different images seen by each eye into a single focused picture.3,4

What is prism correction for double vision?

For people with double vision that persists and is relatively stable, a special form of glasses with prism correction may help. Prism glasses may not help everyone with double vision, particularly if the degree of double vision changes throughout the day or day to day.4

A prism is a piece of glass or plastic that can be added to eyeglasses lenses. Prisms bend light and change the way it enters the eye. By changing the path of light, a prism lens can adjust where light falls on the structures inside the eye. This can help correct double images into a single focused image.3,5

Will prism glasses help me?

If your double vision varies throughout the day or from day to day as is common in MG, prism lenses may not be helpful. This is because different prism lenses are needed to optimally correct different degrees and directions of double vision. If prism lenses are not for you, using an eye patch while watching TV or reading may help relieve double vision. Rest your eyes regularly to help with eye fatigue.4,6

How do I know if prism glasses are a choice for me?

You will need an eye exam to find out if prism correction could help with your vision problems. Your eye doctor will ask you questions and perform several different eye tests to determine if prisms may help with your type of double vision.3

If your doctor recommends prism correction, the prism is added to a regular eyeglass lens. Sometimes a temporary lens is used to determine if a prism will improve your vision. It is normal to feel eye strain with a new prism eyeglass lens.3

Possible side effects of prism vision correction include:3

  • Nausea
  • Headache
  • Eye pain
  • Increased double vision

A prism lens prescription may cause eye strain for a few days. Call your eye doctor to discuss your options if you have difficulty adjusting to a new prism lens.3

How do I find an eye doctor that understands myasthenia gravis?

Doctors that specialize in eye problems related to the nervous system (including MG) are called neuro-ophthalmologists. The North American Neuro-Ophthalmology Society can help you find an eye doctor specializing in eye problems experienced by people with MG.7

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