Refractive Error after Toric Intraocular Lens Implantation in a Patient with Bilateral Posterior Keratoconus

Purpose: To report a case of bilateral posterior keratoconus where a targeted spherical equivalent outcome was achieved after bilateral cataract surgeryCase summary: A 64-year-old female patient presented with impaired vision. Corrected visual acuity was 0.6 × -2.50 D Ax 60° in the right eye and 0.4 × -2.50 = -2.50 D Ax 140° in the left eye. Although slit-lamp examination revealed no abnormalities on the anterior surface of the cornea, it showed subepithelial opacity and excavation in the central posterior cornea; hence, a diagnosis of posterior keratoconus was made. Corneal tomography revealed that the astigmatism was less than 1 D in the posterior axial curvature map, the size of the posterior corneal elevation was small (right eye, 1.5 mm; left eye, 1.0 mm), and there was no astigmatism in the posterior elevation map. Simulated keratometry was used for the K value, and the intraocular lens (IOLs) power was calculated using the Sanders Retzlaff Kraff/Theoretical formula. The use of toric IOLs was decided to correct anterior cornea astigmatism, and the postoperative target spherical equivalent outcome for both eyes was planned as emmetropic. Finally, the corrected visual acuity was 0.8 × -1.25 D Ax 10° in the right eye and 0.7 × plano in the left eye, resulting in the targeted postoperative spherical equivalent outcome.Conclusions: To determine the most appropriate power of the IOLs in patients with posterior keratoconus, the abnormality of the anterior corneal surface, degree and extent of posterior corneal excavation, and degree of posterior corneal astigmatism should be considered.