In the calculation of IOL power using the SRK/T formula, which parameter's measurement error causes the greatest magnitude of refractive surprise postoperatively?
- A Anterior chamber depth
- B Corneal curvature (keratometry)
- C Axial length ✓
- D Lens thickness
Correct answer: C. Axial length
Explanation
Axial length measurement error is the most significant source of IOL power calculation error. A 1 mm error in axial length results in approximately 2.5–3 diopters of refractive error postoperatively. Keratometry errors of 1 D produce approximately 1 D of refractive error. This is why optical biometry (IOLMaster, Lenstar) using partial coherence interferometry is preferred over immersion ultrasound (A-scan) for its greater axial length measurement accuracy (+/- 0.02 mm vs 0.1 mm), particularly in long/short eyes.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.