Ray-tracing analysis of intraocular lens power in situ

PURPOSE: To describe a method for back-solving the power of an intraocular lens (IOL) in situ based on laser biometry and ray-tracing analysis of the pseudophakic eye. SETTING: University Eye Clinic, Aarhus Hospital, Aarhus, Denmark. DESIGN: Evaluation of diagnostic test or technology. METHODS.: This study comprised pseudophakic eyes with an IOL power ranging from -2.00 to +36.00 diopters (D). Preoperatively, the corneal radius was measured with conventional autokeratometry and the axial length (AL) with optical biometry. After surgery, the position of the IOL was recorded using laser interferometry. Based on the postoperative refraction and the biometric measurements, a ray-tracing analysis was performed back-solving for the power of the IOL in situ. The analysis was performed assuming pupil diameters from 0.0 to 8.0 mm with and without correction for the Stiles-Crawford effect. RESULTS: The study evaluated 767 pseudophakic eyes (583 patients). Assuming a 3.0 mm pupil, the mean prediction error between the labeled and the calculated IOL power (+/- 1 standard deviation [SD]) was -0.26 D +/- 0.65 (SD) (range -2.4 to + 1.8 D). The prediction error showed no bias with IOL power or with AL. The calculated IOL power depended on the assumed pupil size and the Stiles-Crawford effect. However, the latter had a modulatory effect on the prediction error for large pupil diameters (>5.0 mm) only. CONCLUSION: The optics of the pseudophakic eye can be accurately described using exact ray tracing and modern biometric techniques.