Inter-eye difference of the intraocular lens power calculation in a case with bilateral posterior keratoconus

Abstract

Purpose: To report a case with bilateral circumscribed posterior keratoconus with different results of refractive error between eyes after cataract surgery. Case summary: A 57-year-old man was referred for decreased vision and suspected keratoconus in both eyes. The corrected visual acuity was 0.04 in the right eye and 0.2 in the left eye. On slit-lamp microscopy and anterior-segment optical coherence tomography (AS-OCT) examination, the excavation of the posterior corneal surface was observed in the central area of the right eye and in the mid-to-inferior area of the left eye. Considering the posterior corneal refractive power measured within the 8-mm zone on AS-OCT, we expected the postoperative hyperopic shift in the refractive error of 2.61 diopters (D) in the right eye and 2.17 D in the left eye. Accordingly, the adjusted predicted refractive error was determined as -0.68 D in the right eye and -1.06 D in the left eye, based on the Barrett Universal II formula. The postoperative values of the spherical equivalent by manifest refraction was -1.0 D in the right eye and -3.0 D in the left eye at 1 month, which was close to the predicted target in the right eye, but myopic by approximately 2.0 D in the left eye, compared to the predicted values. Conclusions: In patients with bilateral circumscribed posterior keratoconus, the location, depth, and area of the excavation of the posterior corneal surface should be considered independently in both eyes to calculate the intraocular lens power more accurately. © 2021 Korean Ophthalmological Society (KOS). All rights reserved.