Looking for something?

Find it in our extensive resource library!

Smart Filters

  • Reset
  • Services

  • Who it's for

  • What it’s about

  • Format

View: 601

Download: 3

Fitting prisms – base in

It is important that you fit your prism in the correct orientation so please check the prism for where it is marked ‘BASE‘.

Photograph of prism with 'base' written on the bottom left

In your case the prism needs to be positioned ‘base in’. This means that the part marked ‘base’ needs to be positioned towards the nose piece of the glasses. You can also hold the prism up to see which side is the base.

Diagram of side view of prism, as a series of triangles facing the same direction and 'base' written on the right

Side view of prism

If you feel the prism, there is a rough side and a smooth side. The smooth side needs to be positioned against the inside of the glasses.

Photograph of drawing on prism the shape of glasses to size

Using a felt tip pen or a biro, mark the prism to the size of the glasses frame, then remove the prism and cut to size. It will cut easily using a small pair of scissors.

Photograph of cutting prism to size and shape of glasses

You then need to put a small amount of water onto the inside of the clean glasses lens and press the smooth side of the prism down onto the water. You will be able to slide the prism around into place until it is dry. Once dry, it will be fixed well on to the lens.

Photograph of water on glasses to fit prism and move into place  Photograph of prism on glasses

If you need any further help please call the department on 0114 271 7468 and we can talk you through the process.

Is something missing from this resource that you think should be included? Please let us know

Contact us


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: EYE68

Resource Type: Article

How useful did you find this resource?*

If you need any further help please call the department on 0114 271 7468 and we can talk you through the process.


Western Bank
S10 2TH

United Kingdom

Switchboard: 0114 271 7000

Interesting Facts

We’ve got a special MRI scanner just for teddies so children can see what it’s like before they have a scan.

Help to transform our extraordinary hospital into something even better.


By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.