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IOL calculation formula by Shammas in patients with myopic LASIK and cataract

Poster Details

First Author: J.Aronés Santivañez SPAIN

Co Author(s):    A. Dyrda   D. Nahra Saad           

Abstract Details


To know the refractive outcome of cataract patients after myopic LASIK with the use of Shammas method of calculating intraocular lens (IOL).


Consorci Parc de Salut Mar, Hospital Esperanza, Barcelona, Spain


11 eyes of 7 patients with prior myopic LASIK were studied. The mean age of the group was 60.3 years and all patients had cataract. There was no preoperative corneal power or refractive change available. All patients underwent biometry with IOL Master and calculation of the IOL by Shammas method was performed. Data as the axial length (AL), postoperative anterior chamber depth (C: A constant 0.58385x -64.40), the corrected K (Kc: 1.14K post -6.8) and the desired refraction (R) which in our case was -0.5 were used. All patients underwent uncomplicated phacoemulsification and IOL implantation and spherical equivalent was calculated. Prediction of refractive error was also estimated.


The mean values of AL, K1 and K2 were 26.9 mm, 38.18 D, 39.46 D respectively. Mean power of IOL calculated with IOL Master was 17.3, while with Shammas, using as well data provided by IOL Master, was 20.31. We found a mean postoperative spherical equivalent -0.95D +/- 0.78 (SD), with outliers -2.25D and +0.25 D, with an arithmetic error regarding the desired refraction (-0.5) of-0.68D +/-0.52(SD).


One of the most important assessments for the success of cataract surgery is that residual refractive error after intraocular lens (IOL) implantation should be near to emmetropia. In order to do so, calculation of the IOL power should be as accurate as possible. A special dilemma arises in eyes that have previously had refractive surgery. It is because of a high visual quality demand in the group of patients which opted for LASIK and because of the lack of data prior to refractive surgery. There are many different methods to calculate IOL after refractive surgery, one of them is Shammas, used in patients after LASIK. According to our results this formula can be a useful and easy tool for calculating IOL in patients with myopic LASIK when no preoperative corneal power nor refractive changes are available.

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