Bicylindric IOL power calculations
Using both the steep and flat meridians in intraocular lens (IOL) power calculations can improve the reliability and precision of cataract surgery
Jorge Calvo-Sanz MD
Using both the steep and flat meridians in intraocular lens (IOL) power calculations can improve the reliability and precision of cataract surgery, said Jorge Calvo-Sanz MD, Institute Of Visual Sciences, Hospital La Zarzuela, Madrid, Spain.
“The bicylindric method of intraocular lens power calculation is a simple and reliable way to predict the final refractive outcomes in patients with low corneal astigmatism,” Dr Calvo-Sanz told the 22nd ESCRS Winter Meeting in Belgrade, Serbia.
He presented a study in which he compared the predictability of bicylindric IOL power calculations with that of the Haigis formula in 62 eyes of 62 patients with a mean age of 71.63 years (49 to 87 years.).
The patients in the study had no previous ocular surgery or ocular pathology other than cataract. In addition, all had an axial length greater than 21mm, a flat keratometry axis between 0 and 90º. Optical biometry was performed using IOLMaster700 (Carl Zeiss Meditec). All patients underwent implantation of an acrylic monocular lens through a 2.8 mm clear paralimbal corneal incision at 135º.
Four weeks after surgery, the mean difference between the spherical equivalent predicted by the Haigis formula (HSE) and that achieved (ASE) was -0.117 D (p=0.002), whereas the mean difference between the spherical equivalent predicted by the bicylindric approach (BSE) and the ASE was -0.054 D (p=0.009).
Furthermore, the percentage of patients who achieved predicted refraction by the Haigis and the bicylindric method was 76.70% and 84.30% respectively. Moreover, the linear correlation between BSE and ASE was positive and statistically significant (R=0.809, p<0.001), but the correlation between HSE and ASE was also positive but not statistically significant (R=0.083, p=0.520).