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Prism adaptation

What is a squint?

A squint where the eyes do not align as normal. One eye appears straight and the other eye drifts in a different direction.

This can happen intermittently or all of the time. Some squints appear obvious when looking into the distance or close up, while others are the same at all distances. For some children the squint becomes more noticeable when they are tired, ill, focusing on near objects, looking into the distance, daydreaming, or in bright sunlight.

What are the symptoms?

Children with a squint rarely complain of any problems, although some are conscious of when their eye is drifting.

Sometimes children complain of double vision or are aware when their eye is drifting. This can make them close one eye.

How is a squint treated?

There are a variety of treatments depending on:

  • the type of squint
  • the underlying cause
  • the amount that the eye drifts
  • how often the eye drifts
  • how well they can control their eyes

Treatments include:

  • glasses
  • exercises
  • surgery to help straighten the eyes

Your orthoptist and ophthalmologist will advise you which of these is appropriate for your child.

What is prism adaptation?

Prism adaptation is a type of treatment which involves wearing plastic prisms on a pair of glasses. These glasses can either your child’s own or a pair that we will lend to you.

What does prism adaptation do?

The prisms bend light so we can see how your child’s eyes respond to having a squint corrected. The prisms trick the brain into thinking that the eyes are in a straighter position. This will help us to check how well the eyes can work together as a pair and to measure the maximum amount that the eyes drift.

We will use this information to make decisions about how best to treat the squint. If you are having surgery, these measurements will be used by your Ophthalmologist to decide on the type and amount of surgery is needed.

What do you need to do?

Your child’s orthoptist will fit a plastic prism (a clear plastic sheet) to the inside of one or both glasses lenses (on either your own pair of glasses or a pair that we will lend you). Your child will need to wear the prisms on their glasses all of the time until their next appointment. This will help their eyes to get used to wearing the prisms.

The process may be repeated several times over a few appointments because the strength of the prisms may need to be changed as your child’s eyes get used to the prisms.

Some children will have double vision when they first start wearing prisms. Although this can be a little odd at first, it should settle down after a few days. It is perfectly normal for vision to be a little blurry and for a squint to look bigger than usual when wearing prisms.

If we have lent you some glasses for prism adaptation, you will need to return these at the end of the prism adaptation period.

What if the prism falls off or the glasses get broken?

Please get in touch with the eye department as soon as possible if the prism falls off the glasses or the glasses get broken.

Your orthoptist will be able to advise the best course of action if this happens.

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Please note: this is a generic information sheet relating to care at Sheffield Children’s NHS FT. These details may not reflect treatment at other hospitals. This information is not intended as a substitute for professional medical care. Always follow your healthcare professionals’ instructions. If this resource relates to medicines, please read it alongside the medicine manufacturer’s patient information leaflet. If this information has been translated into another language from English, efforts have been made to maintain accuracy, but there may still be some translation errors. If you are unsure about any of the guidance in this resource or have specific questions about how it relates to your child, always ask your healthcare professional for further advice.

Resource number: EYE52

Resource Type: Article

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Please contact the Eye Department if you have any questions or problems with your prism on 0114 2717468


Western Bank
S10 2TH

United Kingdom

Switchboard: 0114 271 7000

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