SRK/T formula accuracy linked to corneal power

This retrospective study found that the accuracy of the SRK/T formula for IOL calculation decreases when the cornea becomes steep or flat. When the predicted refractive error is myopic, a smaller A-constant is needed. However, when the predicted refractive error is hyperopic, a larger A-constant is needed. Therefore, using different A-constants based on the average corneal power can increase the accuracy of the IOL power calculation in the SRK/T formula.

The authors reviewed the charts of 637 patients who underwent uncomplicated phacoemulsification with implantation of the Acrysof IQ or Akreos AO IOL by a single surgeon.

When average corneal power (K) was 44.2 D in the IQ group and 44.0 D in the AO group, the predicted refractive error was smallest. The refractive outcomes became more myopic as K increased from 44.2 D in the IQ group and 44.0 D in the AO group. Refractive outcomes became more hyperopic as K decreased from 44.2 or 44.0 D in the IQ and AO groups, respectively.