How to understand it
A prism dioptre is not the same quantity as spherical lens power. The prescriber decides whether and how prism is used.
An example
An amount without a base direction is incomplete, just as a direction without an amount is incomplete.
A common mix-up
Do not choose prism from an online symptom list or use it to self-treat new double vision.
See the idea in a full guide →
Sources & verification
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