Does Sanders-Retzlaff-Kraff (SRK-2) formula suit a Sri Lankan population in phacoemulsification cataract surgery of medium axial length?

Abstract

INTRODUCTION: After introduction of phacoemulsification with small incision techniques, intraocular lens (IOL) power calculation predictionhas become a crucial step for good refractive outcomes. SRK-2 formula is widely used for that purpose in many locations. AIMS: To evaluate the predictive accuracy of post operative refraction using SRK-2 formula in phacoemulsification of eyes with 22-26mm axial length. METHODS: Patients with senile cataracts undergoing phacoemulsification and IOL during 2011 in Gampaha district by a single surgeon were selected randomly. Single examiner measured simulated manual keratometry preoperatively, seven days postoperatively. Uncorrected visual acuity, slit lamp examination of anterior segment and best spectacle-corrected visual acuity (BSCVA) were measured. The implanted IOL power was used to calculate the predicted postoperative refractive error using time SRK-2 formula. RESULTS: Of 274 patients (56% females, mean (SD) age 65.3(10) years), the right eye was operated in 142(51.8%). On postoperative seventh day, 79% had VA of 6/6 and 14% to 6/9, 4% to 6/12 to 6/36 in the operated eye. Mean (SD) of IOL power used 21.50 (1.90)D. The predicted refractive error with SRK-2 was -0.3(0.145)0 and the achieved refractive error was -0.22(0.732)0. Difference between predicted and achieved refractive error presented a slight hyperopic shift (mean(SD) 0.054(0.397)0}. There was a negative Pearson correlation (-0.126) between the predicted refractive error and achieved refractive error (p=0.04). Predictive error was less than 0.5 in 80.2%, <0.75 in 88.6% and <1.0 in 96.7%. CONCLUSIONS: SRK-2 formula is a good option to predict the refractive error after cataract extraction by phacoemulsification in eyes with medium axial length.