For the correction of astigmatism at the time of cataract surgery, toric IOLs can be an excellent option. The best candidates have a stable, regular, symmetric degree of astigmatism that is consistent in magnitude and direction on multiple biometric machines. It is important for all cataract surgeons to understand how to use these IOLs.
A few key points for the residents in training:
- the toric correction on the IOL does not change the overall spherical equivalent power of the IOL. If you calculate that a +21.0 D IOL will give a plano spherical equivalent outcome, then a sister toric IOL of +21.0 with +2 of astigmatic correction will still give the plano spherical equivalent outcome. This +21.0 D IOL has a power of +20.0 in one meridian and then 90 degrees away the power is +22.0, hence the +2 of astigmatic correction.
- you must remove all viscoelastic from the posterior surface of the IOL optic and from within the capsular bag so that the IOL is less likely to rotate out of alignment. You want the acrylic material of the optic to touch the posterior capsule without any viscoelastic between the two.
- toric IOLs work best with a consistent and overlapping capsulorhexis and your incision should be of proper architecture as well. An irregular incision will induce astigmatism that may throw off the results. In addition, any leakage from the incision will cause the AC to shallow in the immediate post-op period, even if temporarily, and that can allow the IOL to mis-rotate.