Intraocular lens power calculation in cases with posterior keratoconus

PURPOSE: To compare the calculation errors of intraocular lens (IOL) power in patients with posterior keratoconus and to determine which corneal refractive power is suitable for these calculations. SETTING: Chukyo Hospital, Nagoya, Japan. DESIGN: Retrospective case series. METHODS: This retrospective chart review was performed to identify eyes diagnosed with posterior keratoconus using anterior segment optical coherence tomography (AS-OCT). The keratometry (K) values were measured using an autokeratometer and partial coherence interferometry (PCI) (IOLMaster). The AS-OCT measured the total refractive corneal power and the anterior to posterior corneal curvature (A/P) ratio. Predicted refractive errors were calculated from K values based on the postoperative subjective refractive errors. RESULTS: The chart review of 4621 eyes found that 4 eyes of 4 patients (mean age 74.8 years ± 13.0 [SD]) were diagnosed with posterior keratoconus. The total refractive corneal power values were the smallest among all of the corneal refractive powers in all 4 eyes. The preoperative A/P ratio was 1.45 (Case 1), 1.26 (Case 2), 1.25 (Case 3), and 1.44 (Case 4). When the PCI measured K values were applied for the IOL power calculations, all of the eyes became hyperopic with postoperative refractive errors of +1.51 diopters (D) (Case 1), +0.34 D (Case 2), +0.97 D (Case 3), and +1.08 D (Case 4). When the total refractive corneal power values were applied, the errors were +0.10 D (Case 1), -0.18 D (Case 2), -0.61 D (Case 3), and -0.65 D (Case 4). CONCLUSION: The real corneal power values that take both the anterior and posterior corneal curvatures into consideration should be applied for IOL power calculations in cases with posterior keratoconus. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.