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Correcting Defects of Vision

Physics: AQA A Level, topic 10.1.4

Astigmatism Prescriptions

A prescription for astigmatism contains three terms: S, C and A.

S

S

  • The 'spherical' part of the prescription in dioptres, ie the short or long sightedness correction.
C

C

  • The degree of astigmatism, also measured in dioptres.
A

A

  • The orientation of astigmatism from 0 to 180 degrees.
Example prescriptions

Example prescriptions

  • E.g. -2.00 +1.50 × 180
  • E.g. +3.50 +3.00 × 45

Test yourself on Correcting Defects of Vision

  • For the following prescription, what is the long or short sightedness correction?
    +3.50 +3.00 × 45

  • For the following prescription, what is the degree of astigmatism?
    +3.50 +3.00 × 45

  • For the following prescription, what is the orientation of astigmatism?
    +3.50 +3.00 × 45

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