Abstract
With more than 1.5 million Small Incision Lenticule Extraction (SMILE) procedures having already been performed worldwide in an ageing population, intraocular lens (IOL) power calculation in post-SMILE eyes will inevitably become a common challenge for ophthalmologists. Since no refractive outcomes of cataract surgery following SMILE have been published, there is a lack of empirical data for optimizing IOL power calculation. Using the ray tracing as the standard of reference – a purely physical method that obviates the need for any empirical optimization - we analyzed the agreement of various IOL power calculation formulas derived from the American Society of Cataract and Refractive Surgeons (ASCRS) post-keratorefractive surgery online calculator. In our study of 88 post-SMILE eyes, the Masket formula showed the smallest mean prediction error [−0.36 ± 0.32 diopters (D)] and median absolute error (0.33D) and yielded the largest percentage of eyes within ±0.50D (70%) in reference to ray tracing. Non-inferior refractive prediction errors and ±0.50D accuracies were achieved by the Barrett True K, Barrett True K No History and the Potvin-Hill formula. Use of these formulas in conjunction with ray tracing is recommended until sufficient data for empirical optimization of IOL power calculation after SMILE is available.
Highlights
Since its commercialization in 2011, small incision lenticule extraction (SMILE) has become an integral part of modern keratorefractive surgery
Ray tracing was considered the benchmark to compare the agreement of seven formulas available in the ASCRS post-keratorefractive surgery intraocular lens (IOL) power online calculator in post-Small Incision Lenticule Extraction (SMILE) eyes
The ray tracing method represents an alternative to post-keratorefractive surgery IOL power calculation formulas that include “fudge factors”, since this purely physical approach obviates the need for any empirical optimization and does not require any preoperative data
Summary
Since its commercialization in 2011, small incision lenticule extraction (SMILE) has become an integral part of modern keratorefractive surgery. Ray tracing represents a purely physical approach for IOL power calculation attractive in eyes with previous LASIK or PRK6–10 This method involves direct measurement of the posterior corneal curvature (e.g. with Scheimpflug tomography) and obviates the need for historical clinical data. In the absence of sufficient clinical data for empirical optimization of our IOL power calculation, we must either utilize a physical approach (i.e. ray tracing) or rely on the aforementioned formulas optimized for Excimer-based photoablative procedures. The validity of these formulas in post-SMILE eyes seems questionable, as SMILE produces significantly different corneal shape changes as compared with fs-LASIK. The results of this study may provide clinicians with guidance for their first IOL power calculations in cataractous post-SMILE eyes
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