Analysis Of Precision In Predicting Intra Ocular Lens Refractionin Silicon Oil Tamponade

Objective: There is a general tendency in present in clinical in applying to the datas measured before the time being filled with silicon oil or depending on the other healthy eye in the aspect of predicting the IOL power in silicone oil-filled eyes,which often diviated apprently from the predicted refraction.The purpose of this study was to analysis the precision in which IOL power were calculated through a mathematical correcting formula by comparing different methods.Moreover,this study also evaluated the therapeutic effect of combined silicone oil removal and IOL implantation in the eyes with silicone oil tamponade.(combined with cataract extraction in parts),providing with a certain experience for the similar works.Methods: The selected cases(25eyes) were divided into two groups which had no significant difference with the matched age,refraction,the time period after being filled with silicone oil and grads of PVR from January 2005 to November 2006. A groups as contral groups adopted the results measured before the time being filled with silicone oil( or measured depending on the healthy eye in cases of no preordaining).B groups,formula groups, adopted a mathematical correcting formula to calculate the IOL power. Formula,as being followed: (axial length of silicon oil-depth of anterior chamber-thickness of lens)×990/1532+ depth of anterior chamber +thickness of lens=actual axial length .The ultra sonograph automatically calculated the IOL power according to the formula of SRK-T.The predicted refraction both two groups was–1.5D.Both groups underwent combined silicone oil removal through the ciliary body flat incision and IOL implantation(combined with phacoemulsification in parts). The mean follow-up period after the operation was 5 months (range,2-12 months). postoperativebest visual acuity refraction and complications were observed. Making use of the software of spss 11.5 and independent samples T test in statistics, pre- and post-operative visual acuity,refractive states after operation and diviation from predicted refraction were compared between two groups.Results: Of the contral group ,the mean diviations from predicted refraction were about 2.0D.Of the formula group ,the mean were no more than 1.0D(0.94D). Formula group prior to contral group. However,there had not significant difference between contral group and formula group in this point(P=1.594 >0.05). It is believed that this is relation to the little numbers involved in this research..it is supposed to select more samples in the futue.Conclusion: The mathematical correcting formula in predicting IOL power is a precise and effective method and can be wildly used. But it was constrained under some certain conditions.