Optimized Phakic IOL Calculations
Narrative Responses:
Purpose
To identify and quantify sources of random and spurious error in the refractive outcome of phakic IOL procedures
Methods
Means and standard deviations (SDs) of parameters that influence refractive outcomes were taken from the literature or from more than 8000 cases of phakic IOL cases in the STAARVision online database. Surgically induced corneal change was estimated from the subset of cases for which both pre- and postop-keratometry was recorded.The partial derivative of each parameter with respect to spectacle refraction and its SD was used to calculate the relative error contribution.
Results
Preoperative estimation of refractive error and vertex distance are the largest contributors of error.
Conclusion
Improvement in outcome requires judicious selection between refraction type (cycloplegic vs. non-cycloplegic vs. SCTL over-refraction) and better methods for measuring refractive error and vertex distance. Reducing these error sources can reduce mean absolute error to 0.4 D. Surgically induced changes to the cornea contribute less that 0.2 D to the mean absolute error. Errors up to 2 D may result from assuming the vertex distance in all patients is 12.5 mm.