A patient's spectacle prescription is -3.00 DS/-1.50 DC × 90. Converting this to the cross-cylinder (power cross) notation, the power meridians are:

• A Vertical meridian (90°): -4.50D; Horizontal meridian (180°): -3.00D
• B Vertical meridian (90°): -3.00D; Horizontal meridian (180°): -4.50D ✓
• C Vertical meridian (90°): -1.50D; Horizontal meridian (180°): -3.00D
• D Vertical meridian (90°): -3.00D; Horizontal meridian (180°): -1.50D

Explanation

In a minus cylinder prescription -3.00 DS/-1.50 DC × 90, the cylinder axis at 90° means the cylinder acts in the 180° meridian (power of cylinder is perpendicular to its axis). Power in 180° = sphere + cylinder = -3.00 + (-1.50) = -4.50D. Power in 90° = sphere alone = -3.00D. Therefore: vertical (90°) = -3.00D and horizontal (180°) = -4.50D. The steeper correcting meridian (more minus) corrects the flatter corneal meridian.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.