Comparison between laser-predicted ablation and corneal stroma changes measured with a combined scheimpflug and anterior segment OCT topographer after myopic corneal refractive surgery
First Author: J.Alio Del Barrio SPAIN
Co Author(s): M. Canto-Cerdan M. El Bahrawy J. Alió
To compare the predicted stromal ablation provided by a femtosecond laser platform for SMILE (Visumax) and an excimer laser platform for LASIK (Schwind Amaris) with the actual stromal change (preop versus postop) measured with a combined anterior segment OCT and Scheimpflug topographer (MS39, CSO) after myopic refractive surgery.
Vissum Corporación and Universidad Miguel Hernández, Alicante, Spain.
220 operated eyes from 110 myopic patients were analyzed. 47.7% were women and 52.3% were men, with age range between 20 and 56 years. They were divided into groups according to the surgical technique (109 received SMILE and 111 FemtoLasik). All patients had complete visual and refractive examination preoperatively and at 1, 3 and 6 months postoperatively. Predicted stromal ablations by both laser platforms (Visumax for SMILE cases and Amaris Schwind for LASIK cases) were recorded at the time of surgery. Postoperative stromal changes were measured using the MS39 topographer at the same time points.
Spherical equivalent at 6 months changed from -4.88±1.92D to -0.04±0.43D in the SMILE group, while in the FemtoLasik-group changed from -3.19±1.78D to -0.01±0.36D. Mean predicted stromal ablation by the Visumax for SMILE was 109.42±26.88µm while a central corneal stroma change of 106.12±27.01µm was obtained with the MS39. Amaris-Schwind mean predicted ablation was 63.78±28.11µm and MS39 encountered a central stromal change of 64.43±29.77µm. Differences were 2.43±3.74µm for SMILE and -0.11±3.40µm for femtoLASIK. These differences between laser-predicted and MS39-measured stromal ablations were statistically-significant for SMILE(p<0.05) but not for FemtoLasik (p>0.05).
MS39 can accurately measure corneal stroma changes after ablative corneal refractive surgery for myopia. While in femtoLASIK predicted and obtained stromal ablations are equivalent and comparable, we observed a statistically significant underestimation of 2.43µm in the predicted stromal ablation provided for myopic SMILE.