Dr. Kohnen provided an example of a patient whose total corneal refractive power showed an interaction between the sagittal and posterior maps. In one eye, the SimK astigmatism was 2 D, while the total corneal refractive power was 2.1 D.
The second eye had a SimK astigmatism of 0.1 D on the anterior surface and the posterior surface had a total corneal refractive power of 1 D. "So there comes the distinction between these two measurements," said Dr. Kohnen.
Summarizing, Dr. Kohnen advised physicians to pay attention to whether astigmatism is regular or irregular in their patients, to factor in posterior corneal astigmatism, to measure total corneal refractive power, and consider the toricity of the IOL.
"Figure this out with your own results," Dr. Kohnen said. "Monitor them. And, of course, don't underestimate the effect of astigmatism with multifocal IOLs."
Looking ahead, Dr. Kohnen predicted that small-aperture IOLs will play an increasingly important role. "It takes a lot of the aberrations away and might be the future for treating very irregular corneas," he added.