A patient's cycloplegic refraction reveals -3.00 DS / -1.50 DC × 90°. The cylinder axis at 90° means the more myopic meridian (steeper corneal curvature) is located at:

• A The vertical meridian (90°)
• B The horizontal meridian (180°)
• C The oblique meridian (45°)
• D The axis of the cylinder; the steeper meridian is perpendicular to the axis at 180° ✓

Explanation

In a minus cylinder notation, the cylinder axis denotes the meridian of least power (flattest), and the meridian of greatest refractive power (steepest, most myopic) is perpendicular to the axis. With the axis at 90°, the cylinder acts along the 180° meridian (horizontal), meaning the horizontal meridian is more myopic. This is simple myopic astigmatism of the against-the-rule type (steeper horizontal meridian). This distinction is essential for prescribing spectacles and planning refractive surgery.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.