IOLMaster keratometry for the calculation of toric intraocular lens power and orientation

In the implantation of intraocular lenses (IOL) stringent requirements are made on achieving the refractive target. This necessitates the exact determination of the basic data needed for IOL power calculation – both the axial length and, in particular, the corneal power – and additionally the cylinder power and its axis in the case of a toric lens. This gives rise to the question, especially for the implantation of toric lenses, as to what instrument system is more suitable: a topography system, a manual keratometer or the keratometer of the IOLMaster on the basis of the reproducibility of individual measurements. The reproducibility of the measurement of the spherical equivalent (SE) with the IOLMaster – here the mean difference between the minimum and maximum SE of 3 individual measurements per eye – was 0.09 ± 0.06 D [0 – 0.52]. The deviations within one measurement series were very low: in 79% the deviations were lower than 0.125 D, in 93% lower than 0.25 D, in 99% lower than 0.50 D and in 100% lower than 1.00 D. The reproducibility of the measurement of the power of the astigmatism – here the mean difference between the minimum and maximum astigmatism of 3 individual measurements – was 0.21 ± 0.17 D [0 – 1.35]. The deviations of the measured values in the measuring series were low here also: 43% lay within 0.125 D, 74% within 0.25 D, 92% within 0.50 D and 99% within 1.00 D. The reproducibility of the axis measurements was dependent on the power of the astigmatism. IOLMaster keratometry for the calculation of toric intraocular lens power and orientation Wilfried Bissmann, PhD, Marcus Blum, MD, Kathleen S. Kunert, MD The deviation between the maximum and minimum axial values for astigmatisms from 0.76 D were smaller than 5 degrees on average and smaller than 2 degrees on average from 2.5 D. In regard to the clinical requirements the IOLMaster demonstrated its suitability for measuring exact basic data for the calculation and implantation of toric intraocular lenses. The importance of toric intraocular lenses for the correction of higher astigmatism, and of cataract patients in particular, is growing. In the past 10 years the IOLMaster has become established as the gold standard for biometry and IOL power measurement and helps to obtain optimal refractive outcomes after intraocular lens implantation. While only the mean corneal power is of significance in the IOL power calculation of spherical lenses, the power and position of the corneal astigmatism plays an additional important role in the implantation of toric lenses. To determine the basic data for the calculation of a toric IOL, manual and automatic keratometers and topography systems are available. A retrospective clinical study is aimed at clarifying to what extent keratometry with the IOLMaster clinically provides sufficiently exact values for calculating the power of a toric intraocular lens, as well as an adequately exact axis for the implantation. The measured values obtained are compared with the clinical requirements. 1) Wilfried Bissmann, Carl Zeiss Meditec AG 2) Marcus Blum und Kathleen S. Kunert, HELIOS Klinikum Erfurt, Eye Clinic