Background Silicon oil tamponade eyes following vitrectomy accelerate and induce lens opacification,so the accurate measurement and calculation of intraocular lens (IOL) diopter before cataract extraction+ IOL implantation is very important for the recovery of visual function.Objective This study was to compare the differences of IOL powers measured and calculated by different apparatus and different IOL power formulas before cataract extraction + IOL implantation silicon oil tamponade combined with cataractous eyes.Methods A prospective,consecutive,nonrandomized study was performed.Thirty-six silicon oil tamponade with cataract eyes of 36 patients were included in the Second Affiliated Hospital of Soochow University from August 2011 to October 2013.Patients with silicone oil emulsification for 4 months to 2 years prepared to treat by cataract extraction + IOL implantation+silicon oil removal.Axial length (AL),corneal curvature (CC) and anterior chamber depth (ACD) were measured with IOLMaster and A-scan with manual kerameter (MK) in the eyes for the prediction of IOL power by SRK-Ⅱ,SRK/T,Hoffer Q,Holladay 1 and Haigis formulas under the oral informed consent.The mean predictive error (MPE) and mean absolute refractive error (MAE) between predictive IOL diopters before operation and actual IOL diopters after operation were evaluated.Results The AL and ACD values measured by IOLMaster was (25.43± 0.90)mm and (3.22±0.38)mm,which were significantly higher than (25.21±1.02)mm and (3.07±0.62) mm by A-scan+ MK respectively,the difference between the two measure methods was statistical significance (both at P =0.000).No significant difference was found in measured CC values between IOLMaster and A-scan+MK ([44.58±1.57] D vs.[44.56±1.62] D) (P=0.568).When the parameters measured by IOLMaster were used,the MAE from SRK/T formula was smaller than that from SRK-Ⅱ,Hoffer Q,Holladay 1 and Haigis formulas (P =0.017,0.009,0.012,0.001),and the MAE from Haigis formula was significantly larger than that from SRK-Ⅱ,Hoffer Q and Holladay 1 formulas (P =0.026,0.035,0.021).When measured by A-scan + MK,the MAE from Haigis formula was significantly larger than that from SRK-Ⅱ,SRK/T,Hoffer Q and Holladay 1 formulas (P=0.007,0.004,0.018,0.006).There was no significant difference in the number of eyes with MAE ≤ 1.0 D between IOLMaster and A-scan+MK measurements under the calculation of SRK-Ⅰ,SRK/T,Hoffer Q and Holladay 1 formulas (x2 =0.107,2.250,0.845,0.084,all at P＞0.05).However,the number of eyes with MAE ≤ 1.0 D was significantly increased in IOLMaster measurement compared with A-scan+MK under the calculation of Haigis formula (x2 =4.431,P =0.035).Conclusions In silicon oil-filled cataract eyes,SRK/T formula appears to have a more accurate predictive value of IOL power than that of other formulas when employ IOLMaster;when use A-scan+MK measurement,the predictive value of IOL power seems to be better by using SRK-Ⅱ,SRK/T,Holladay 1 or Hoffer Q formulas.