Ray tracing-based power calculation leads to better refractive outcomes

Nino Hirnschall MD Nino Hirnschall, Vienna Institute for Research in Ocular Surgery, Austria, said there are two potential advantages of a ray tracing-based IOL power calculation. “First, more individual IOL power calculation is possible, for example in eyes with irregular cornea or those eyes who have previously undergone refractive surgery. Second, because it is a purely physical approach, no empirical ‘optimisation’ is required,” said Dr Hirnschall. In the ray tracing-based method, IOL selection is based on predicted visual acuity and a neuronal weighted retinal image quality metric (RIQM). It involves ssOCT-based biometry and keratometry, incorporating anterior and posterior corneal surfaces, corneal thickness, axial length, anterior chamber depth and white-to-white distance. Dr Hirnschall’s team conducted a prospective study of 40 eyes comparing outcomes obtained using the ray tracing method with those obtained with a triple-optimised Haigis formula. “Ray tracing offers more detailed information of the cornea, as well as anatomical data instead of estimated lens position, both of which lead to a better refractive outcome,” said Dr Hirnschall. A potential limitation of the method is that exact IOL design information is needed. Ray tracing resulted in a 2.5% increase in outcomes within 0.5D and 0.75D of target refraction, and a 10% increase in those coming within 1.00D.