Which type of toric IOL orientation error leads to the greatest loss of its intended astigmatism correction?
- A 3° off-axis rotation
- B 10° off-axis rotation
- C 45° off-axis rotation — creates maximum residual astigmatism in opposite axis ✓
- D 30° off-axis rotation
Correct answer: C. 45° off-axis rotation — creates maximum residual astigmatism in opposite axis
Explanation
A toric IOL loses approximately 3.3% of its corrective power for every 1° of rotation from the intended meridian. At 30° off-axis, the toric IOL loses 100% of its intended correction (no net astigmatism correction). Beyond 30°, the lens induces astigmatism at a 90° perpendicular axis — maximally at 45° off-axis where the full toric power manifests as residual astigmatism at 90° to the intended correction axis. Therefore 45° rotation produces the worst outcome with maximum against-the-rule or with-the-rule induced astigmatism.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.