Assessing the Astigmatism Reducing Effect With Toric IOLs in Eyeswith Low Astigmatism

With increasing demands of patients concerning refractive outcome after cataract surgery, toric intraocular lenses (IOLs) that correct corneal astigmatism have been introduced more widely to cataract surgery. Originally, toric IOLs were used mainly for patients with high degrees of astigmatism. Since a couple of years, toric IOLs are available from numerous manufacturers to correct moderate amounts of astigmatism which are much more prevalent with about 8% having a corneal astigmatism of 2.0D or more in the cataract population. 5Using toric IOLs for these eyes results in less spectacle dependence of patients due to the astigmatic correction. Other astigmatism reducing techniques, such as peripheral corneal relaxing incisions and opposite clear corneal incisions were shown to be less predictable. Although the use of toric IOLs became the gold standard to correct corneal astigmatism during cataract surgery , there is still uncertainty, if low astigmatism should be corrected. Visser et al. showed that moderate astigmatism of than 1.5D should be corrected for monofocal IOLs and Hayashi showed that remaining astigmatism of 1.0D already decreases visual quality in eyes with multifocal IOLs. Although correction of low corneal astigmatism appears to be beneficial, some hurdles have to be taken into account. In eyes with low corneal astigmatism the accuracy of measuring the astigmatism meridian is relatively low. Furthermore, different corneal measurement techniques are not always comparable and it is difficult to know, which device shows the correct amount of astigmatism. Additionally, the correction of the spherical equivalent is of high importance, as a refractive surprise will also attenuate the astigmatism reducing effect of the toric IOL. Aim of this study is to assess, if toric IOLs are useful in patients with low amounts of corneal astigmatism and to quantify the sources of error in toric IOL power calculation.