A patient presents with -2.00 DS / -3.00 DC × 180. This prescription can be transposed to the following minus cylinder notation:

• A -2.00 DS / +3.00 DC × 90
• B +2.00 DS / -3.00 DC × 180
• C -5.00 DS / -3.00 DC × 180
• D -5.00 DS / +3.00 DC × 90 ✓

Explanation

Transposition rules: (1) Add the sphere and cylinder algebraically for the new sphere: -2.00 + (-3.00) = -5.00 DS. (2) Change the sign of the cylinder: -3.00 becomes +3.00. (3) Rotate the axis by 90°: 180° + 90° = 270°, but since axes are between 0° and 180°, 270° − 180° = 90°. So the transposed form is -5.00 DS / +3.00 DC × 90. This is now plus cylinder form, confirming the optical equivalence.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.