In calculating IOL power using the SRK/T formula, which biometric variable has the highest influence on the final calculated power?
- A Anterior chamber depth (ACD)
- B Keratometric readings (K)
- C Axial length (AL) ✓
- D White-to-white corneal diameter
Correct answer: C. Axial length (AL)
Explanation
Axial length has the greatest impact on IOL power calculation: a 1 mm error in axial length measurement produces approximately 2.5-3 diopters of refractive error. The SRK/T (Sanders-Retzlaff-Kraff Theoretical) formula, a third-generation formula, uses AL, K, and ACD to predict effective lens position. For extreme AL values (<22 mm or >26 mm), newer formulas (Barrett Universal II, Kane, EVO) outperform SRK/T. Optical biometry (IOLMaster, Lenstar) is significantly more accurate than ultrasonic A-scan for AL measurement due to avoidance of corneal compression.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.