Orthoptic Department
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What is this information about?
This information is about Fresnel prisms. It explains:
- what Fresnel prisms are
- how a Fresnel prism works to improve symptoms of double vision
- how you should care for your Fresnel prism
- how your vision may be if you have a Fresnel prism
- where you can find further information and support
Why have I been given this information?
You have been given this information because:
- your optician, GP or ophthalmologist has referred you (or a family member or someone you are a carer for) to an orthoptist for treatment of your double vision (diplopia). They may have mentioned in their referral that they think that a Fresnel prism may help you.
- you are having an appointment to have a Fresnel prism fitted to your glasses.
Reading this information will help you to know what to expect from having a Fresnel prism fitted and using it.
What is a Fresnel prism?
A Fresnel prism is a plastic membrane (thin plastic sheet) that fits on the inside of your glasses. It can:
- ‘join together’ double vision by moving the images closer together. This means the brain recognises them as a single, rather than double, image.
- relieve symptoms that you may have which are caused by the effort of trying to maintain single vision.
Be aware
– the Fresnel prism can relieve the symptoms of double vision. It is not a cure.
– It will not prevent or delay your recovery from double-vision
– If a Fresnel prism is not right for you for any reason, your orthoptist will not prescribe one.
How long might I need a Fresnel prism for?
This is different for everybody. You are likely to need to wear a Fresnel prism for weeks or months.
You may need to have your prism changed during your treatment for one of a different strength. This is so that it is right for your condition as it changes and you are as comfortable as possible.
If your eye condition remains stable for 6 months or more, we may be able to prescribe glasses for you that will have a prism of the correct strength built-in to them.
For some people we may use a Fresnel prism before they have an operation to correct double-vision or strabismus. This can help us to tell whether an operation is likely to work for them.
How is a Fresnel prism fitted?
1. Your orthoptist will test your vision so that they can tell the strength of prism that is best for you.
2. The correct prism is cut to fit inside your glasses frame, usually to the back surface of the lens.
3. We stick the prism to your glasses (spectacles) using water. This means your glasses will not be damaged at all when the prism is removed. As the water dries, suction holds the prism onto your glasses.
The prism is fitted so that it is lined-up in a way which means it can ‘join’ your double-vision.
How do I clean my Fresnel prism?
Do
- clean your prism using a tiny amount of liquid soap on a damp cloth
- use an old, soft, toothbrush (follow the lines of the prism) to clean in the grooves
- gently pat the prism dry with a soft cloth
Do not
- remove the prism from your glasses to clean it
- put the prism under a running tap
- get the prism too wet while you are cleaning it. Water may seep under the prism and make the prism edges curl or make the prism come off.
What should I do if the prism comes off?
If the prism does come off:
1. put both the glasses and prism in a bowl of water
2. fit the prism onto the lens in the correct position with the smooth side against the lens
3. hold the prism onto the lens and take your glasses out of the water
4. squeeze excess water out from under the prism using a soft cloth.
Might I have blurred vision when I am wearing my prism?
You may notice that your vision is slightly distorted or blurred. This is caused by the prism ridges. If you keep using the prism you are likely to adapt to this over time.
Might I still see double when I am wearing my prism?
The prism works best when you look straight ahead. You may still notice some double vision in some positions. It will help if you turn your head more than usual when you look into these positions.
You will still be aware of double vision when you are not wearing your glasses and prism.
Will my prism always work as well as when I first had it?
Many conditions which cause double vision will change over time. They may get better or sometimes worse.
The strength of your Fresnel prism may need to be adjusted to suit your condition as it changes.
What should I do if I am having problems with my prism or it is no longer comfortable?
Do
- contact your orthoptist for advice.
Contact Details
St Richard’s Hospital Orthoptists
01243 831499
Southlands Hospital Orthoptists
01273 446077
Sussex Eye Hospital Orthoptists
01273 696955
The information in this leaflet is for guidance purposes only and is in no way intended to replace professional clinical advice by a qualified practitioner.
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