Fresnel prisms

If you have any further questions, please ask a member of the eye care team.

What is a Fresnel Prism?

A Fresnel prism is a flexible plastic sheet consisting of tiny prisms.

It is generally applied to one lens (occasionally both lenses) of your glasses . The prism adheres to the lens by suction, using water.

If you do not currently wear glasses then some non prescription glasses will be supplied by the orthoptic department.

How does the Fresnel Prism work?

The Fresnel prism works by bending the light entering the eye.

The Fresnel prism can be used in different ways:

When the eyes have the ability to work together, the prism brings the double images closer together and the brain joins them into a single picture. This allows the eyes to work together again and restores 3-D (stereoscopic) vision.
When the eyes do not have the ability to work together (e.g. if you have had a childhood squint) the prism is used to move the second image into a position where it can more easily be ignored.

Generally, the Fresnel prism will only control the double vision when you are looking straight ahead. You may still get double vision when you look in other directions. Your symptoms will only be controlled when the prism is worn.

Which eye will look through the Fresnel prism?

The Fresnel prism is usually only required over one lens. It does not matter which eye looks through the prism. Most people prefer to have it in front of their worst seeing eye. Using a Fresnel prism will not make your eye weaker, strain the other eye or stop the double vision improving.

The prism may be applied to the entire lens or just a portion of it. If you use bifocals or varifocals you may need different strengths of prism on the reading and distance sections.

Will the Fresnel Prism affect my vision?

Yes, you may notice some slight blurring or distortion of your vision and possibly some rainbow effects in bright light. The stronger the prism, the more you are likely to notice this.

Most people get used to this with time and prefer to have the slight blurring rather than the double vision.

What do I do if the Fresnel prism isn’t helping?

Please contact the orthoptic department for advice if

You are still experiencing double vision when looking through the Fresnel prism
The double vision appears to be getting much worse, both with and without the Fresnel prism.

What do I do if my double vision is getting better?

If the double vision is improving but still present when not looking through the prism, continue with the prism until your next appointment.

If you feel your double vision has resolved you can remove the Fresnel prism from the glasses by placing your finger nail under the edge and peeling it off. Please contact the orthoptic department for further advice.

How long do I wear the Fresnel prism for?

This is different for every person. If your double vision improves then the strength of the prism will gradually be reduced at each appointment.

Generally the prism is worn until the double vision improves completely, or until it has been stable for approximately six months and a more permanent solution is required.

The eye care team will advise you about other possible treatments for double vision.

More information can be found in the double vision leaflet

Long-term the Fresnel prism may be changed to a permanent prism which is built into a pair of glasses and has the advantage that there is no blurring effect.

You will have a full sight test carried out by a hospital optometrist (optician) and will be given a prescription to take to a local optometrist of your choice to have glasses made up.

Once discharged from the eye department your local optometrist will take over management of the prisms.

Can a Fresnel prism be used long term?

Occasionally a very strong prism is required which is too strong to be built into glasses. In this instance a Fresnel prism may be used in addition to or instead of a permanent prism.

If you are discharged from the eye department with a Fresnel prism then your local optometrist will be responsible for ordering a new prism if it needs replacing. You do not need to contact the eye department.

How do I clean the Fresnel prism?

The rough side of the prism can collect dust and grease over time and will become cloudy.

Important

Smoking will cause permanent discolouration of the prism.

The prism can be cleaned in different ways

Without removing it from the lens of your glasses

Hold the prism in place against your glasses with your finger and thumb.
Place prism under a warm running tap or in shallow water and add detergent.
Use an old toothbrush or nail brush to gently scrub the rough side of the prism.
As you hold the prism in place, dry off any excess water with kitchen towel. Press out any air bubbles towards the edge with your finger.

Removal from the lens of your glasses

If the edges of the prism appears to be peeling away, you may need to remove it completely for a thorough clean.

Peel off the prism by placing your fingernail under the edge.
Thoroughly clean the glasses in warm, soapy water.
Use an old toothbrush or nail brush to gently scrub both sides of the prism.
Wet both the lens and the prism with water. The prism has a smooth side and a rough side. Check by gently scraping a finger nail over the surface. Place the smooth side of prism onto the lens and press out any air bubbles towards the edge with your finger.
The prism will have been cut to shape to fit the lens and this should help with reapplying it.
Ensure that the lines on the prism are in the same direction as before and on the same lens.
Dry off any excess water with kitchen towel.

If you immediately experience double vision when you put the glasses on, it may be that the prism in on the wrong lens or is the wrong way round.

What do I do if my prism falls off?

Please read the information about cleaning your prism to help you with this.

If you are still having some problems with your prism, please contact the orthoptic department for advice.

Can I drive wearing a Fresnel prism?

If you are current driver you need inform the DVLA that you have double vision.

You may be able to drive wearing a Fresnel prism depending upon what category of vehicle you are driving e.g. bus/car.

More information about driving and double vision visit the GOV website.

You can also write to the DVLA at:

Drivers Medical Group DVLA
Swansea
SA99 1DF

Telephone: 0300 790 6806

For further information

Contact details

Appointments office:

To change or cancel an appointment: 0191 282 4444

Monday to Friday, 9am to 5pm (excluding Bank Holidays)

Orthoptic department

To speak to an orthoptist about treatment: 0191 282 4434

Monday to Friday, 9am to 5pm (excluding Bank Holidays)

PALS (Patient Advice and Liaison Service) for help, advice and information about NHS services. You can contact them on free-phone 0800 032 02 02, e-mail the North of the Tyne PALS department or text to 07815500015.

If you would like to find accessibility information for our hospitals, please visit the Accessable website.