Value of Two Horizontal Prisms

One prism held over either eye

• One prism held over each eye
• Prisms are assumed to be in the opposite directions over each eye (e.g. both base in or base out)
• Prisms are in the frontal plane position

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Prism Value of One Horizontal Prism Held Over Each Eye

Select Prism 1 (PD):



Select Prism 2 (PD):



The resultant prism power is:

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Adapted From: Thompson & Guyton. Ophthalmic Prisms: Measurement Errors and How to Minimize Them. Ophthalmology 1983;90:204-2010