IOL Power Calculation by Ray Tracing in Eyes with Previous Radial Keratotomy

Background: /Objectives: To evaluate the accuracy of intraocular lens (IOL) power calculation by ray tracing in eyes with previous radial keratotomy (RK). Methods: A consecutive series of patients with previous RK was retrospectively analyzed. Preoperatively, all eyes underwent optical biometry to measure the axial length (AL) and anterior segment imaging by the MS-39 (CSO), which combines Placido disc corneal topography and anterior segment optical coherence tomography. The ray tracing software of the MS-39 was used to calculate the IOL power. For comparative purposes, the results of the Barrett True-K, EVO, Haigis-Total Keratometry and PEARL-DGS formulas were also investigated. The refractive outcomes were evaluated with Eyetemis. Results: Twenty-four eyes (24 patients) were investigated. The mean AL and keratometry were, respectively, 27.34 ±2.88 mm and 35.53 ±3.66 diopters (D). The mean prediction error (PE) was -0.03 ±0.65 D (range: -1.30 to +1.64 D). The mean and median absolute errors were 0.52 and 0.48 D. The percentage of eyes with a PE within ±0.25 D, ±0.50 D and ±1.00 D were 29.17%, 62.50% and 87.50%, respectively. A comparison to the other formulas was possible in 20 eyes and did not reveal any statistically significant differences, although they achieved a lower percentage of eyes with a PE within ±0.50 D (ranging from 50 to 60%, compared to 65% with ray tracing). Conclusions: Ray tracing is a relatively accurate solution to calculate the IOL power in eyes with previous RK. Paraxial formulas provide similar outcomes and should be considered in these patients.