Comparison Between Anterior and Posterior Corneal Astigmatism by Scheimpflug Topographer

[Purpose] We compared the characteristics of anterior and posterior corneal astigmatism. <br>[Subjects and Methods] Subjects were 291 eyes of 204 patients (144 males and 147 females; average age, 67.5 ± 13.9 years) with corneal astigmatism of ≥ 1.00 D measured by an autokeratometer at routine tests before cataract surgery at the Ohshima Hospital of Ophthalmology between July 2012 and July 2013. The subjects had no corneal diseases or any history of previous ocular surgery. To measure corneal astigmatism, the anterior and posterior corneal surfaces were analyzed using the scheimpflug topographer TMS-5 manufactured by Tomey Corp.<br>[Results] The average levels of corneal astigmatism on the anterior and posterior surfaces were 2.08 ± 0.81 D and 0.30 ± 0.10D, respectively. In case of anterior corneal astigmatism, the number of patients having with-the-rule astigmatism decreased while the number of patients having against-the-rule astigmatism increased with increasing age. In patients with posterior corneal astigmatism, 73.2% had against-the-rule astigmatism. Although majority of the patients in all age groups had against-the-rule astigmatism, the percentages of patients having with-the-rule astigmatism and oblique astigmatism increased in elderly patients. Regarding the astigmatism axis, all the eyes with anterior corneal with-the-rule astigmatism axis had posterior against-the-rule astigmatism. In patients with anterior corneal against-the-rule astigmatism axis, 47.1% had posterior against-the-rule astigmatism and that was different from the distribution of posterior corneal astigmatism axis. In addition, a significant correlation between the levels of anterior and posterior corneal astigmatism was seen in the patients with anterior corneal with-the-rule astigmatism axis (r = 0.673, P < 0.01). On the other hand, the same correlation was not seen in the patients with anterior corneal against-the-rule astigmatism axis.<br>[Conclusion] The characteristics of posterior corneal astigmatism could vary depending on the type of anterior corneal astigmatism. This suggested that for the selection of Toric IOL, it is necessary to carefully examine posterior corneal astigmatism using a scheimpflug topographer or anterior segment optical coherence tomography.