The Evaluation of the Difference between the Calculated Estimated Post-operative Refraction and the Real Post-operative Refraction for Five Types Intraocular Lenses

ABSTRACT

PURPOSE: To evaluate and compare the difference of predictive post-operative refraction preoperatively and real post-operative refraction among five types of intraocular lens. METHODS: We reviewed retrospectively 567 cataractous eyes that had undergone phacoemulsification or ECCE with posterior chamber intraocular lens (IOL) implantation by the same surgeon. Applied IOLs were AMO(R) Phacoflex(R) II SI40NB, Acrysof(R) MA60BM, Sensar(TM) AR40e, CeeOn(TM) 811B and CeeOn(TM) 720A. Prediction of post-operative refraction (predictive refraction) was calculated by the SRK/T formula with manufactured A constant. Post-operative manifest refraction (real refraction) was done at least 2 months postoperatively. We compared the difference between the predictive refraction and the real refraction by paired t-test. RESULTS: Total studied eyes were 390 eyes. In all groups, more myopic shift were observed than predicted. In AMO(R) Phacoflex(R) II SI40NB group, statistically significant difference was seen in postoperative manifest refraction over the predictive refraction as much as mean 0.46 diopter myopically (p<0.05, paired t-test), but others were not. In the AR40e implanted group, the error of predictive refraction was the smallest among groups. CONCLUSIONS: Prediction of postoperative refractive state was influenced by various clinical factors. Using a revised A constant, predictive error would be decreased. We recommend that every cataract surgeon had better have one's original A constant over each IOL and A constant may be revised when major surgical or biomedical measurement settings were changed.