Prediction of refractive outcome after cataract surgery using partial coherence interferometry: comparison of SRK/T and Haigis formulae

To compare the accuracy of the predictions of SRK/T and Haigis formulae, incorporating all the parameters calculated using Zeiss IOLMaster Scan, based on partial coherence interferometry, and to analyse the effect of updating or optimisation of the constants on the post-operative result. A retrospective study was done on 51 consecutive patients, who underwent phacoemulsification by a single surgeon with a temporal corneal incision and a standard Alcon Acrysof MA30 implant in the bag. The pre-operative data were measured using Zeiss IOLMaster scan, and the IOL power calculations were done using both SRK/T and Haigis formulae. The final implant power selection was based on SRK/T predictions. The patients were divided into three groups depending on the axial length, and the post-operative results were analysed at 4 weeks. The difference between the predicted value and the post-operative spherical equivalent was calculated for both the formulae, and a paired t test used for significance. The axial length ranged from 20.93 to 25.16 mm. The error for Haigis was less compared to SRK/T overall and SRK/T resulted in an average hypermetropia 0.69 D and Haigis resulted in an average myopia of 0.16 D. The comparison between SRK/T and Haigis and the updated version of both using the paired t test shows a statistically significant difference, the p values being <0.03 and <0.01, respectively. The updated Haigis Formula with the optimised constants was significantly more accurate than SRK/T formula.