Modified SRK formula for axial myopia (24.5 mm < or = axial length < 27.0 mm)

When used for eyes with greater than average axial length (AXL), the SRK formula has been reported to have a tendency to yield more myopic refractions than those predicted. To further evaluate such findings, we studied 609 eyes with AXLs between 24.5 and 27.0 mm. Comparing the predicted with the actual refractions and calculating the range of errors, we found that the postoperative refractions were more myopic than predicted. Then, based on our evaluation of the relationship between the postoperative refractions and the powers of the implanted intraocular lenses (IOLs), we devised the following formula: R = 0.8 x (P - I) + 0.57 (P < .01) in which R = the postoperative refraction; P = the emmetropic IOL power; and I = the actual IOL power. Testing this modified SRK formula in 55 additional eyes, we found that the predicted postoperative refractions it yielded were more accurate than those calculated using five earlier formulas.