Clinical application of bicylindric intraocular lens power calculation method

To analyze the reliability of the refractive results prediction obtained in intraocular lens (IOL) calculation using bicylindric power calculation method, with the use of steep and flat keratometry readings compared with the classical mean keratometry calculation method.

Fifty-seven eyes of 57 subjects who underwent cataract surgery were included in this prospective study. Optical biometry was performed with IOLMaster 700 and IOL power calculation was performed using both keratometry readings and the surgically induced astigmatism. Four weeks after surgery, subjective refraction was done. Finally, results obtained with both IOL calculation methods were compared.

Mean spherical equivalent using bicylindric IOL power calculation method was -0.082 ± 0.296D, and achieved mean spherical equivalent using classical IOL power method with Haigis formula was -0.088 ± 0.405D. Achieved mean spherical equivalent obtained in subjective refraction after surgery was -0.101 ± 0.265D. Linear correlation between bicylindric method spherical equivalent calculation and achieved spherical equivalent was statistically significant (r = 0.761, P < 0.001), also correlation between Haigis spherical equivalent calculation and achieved spherical equivalent was statistically significant (r = 0.339, P = 0.010). Emmetropia was achieved in 49 of 57 (85.86%) subjects and bicylindric method calculated that 49 of 57 (85.86%) of subjects would get emmetropia (P = 1.000). Classical IOL power calculation estimated that 38/57 subjects would get emmetropia (66.67%) (P = 0.026).

The IOL power calculation including both keratometry readings and surgically induced astigmatism seems to be more accurate and provides more precision in refractive prediction than classical calculation method.