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.