Suggested usage for prisms

4 Diopter

The 4 diopter prism can be used to differentially-diagnose between the presence of a microtropia and bifoveal single vision. N.B. A positive response for microtropia is sometimes found with anisometropic amblyopia, the response changes to normal BSV when the correct spectacles are worn.

10 Diopter

The 10 diopter prism is used to indicate the presence of amblyopia when a vision test is not possible. An article on how to perform the test and its efficacy can be downloaded here.

20 Diopter

Use base out in front of each eye to establish the presence and quality of motor fusion. A link to information on how to perform the test correctly can be downloaded here.

15 Diopter

Use instead of a 20 diopter in patients especially those with exophorias, who are unable to overcome a 20 diopter base out prism.