Abstract
Purpose :
The concept of the Planned Optical Zone (POZ) is a pivotal element in refractive eye surgeries. Ideally, the POZ should align perfectly with the Effective Optical Zone (EOZ), which is the actual corneal area reshaped during the surgical procedure. This retrospective study aims to calculate and evaluate the EOZ using a newly developed fully automated method for corneal lenticule extraction treatments.
Methods :
The clinical data for this retrospective study comes from treatments using a lenticule extraction femtosecond laser system (SmartSight using SCHWIND ATOS, SCHWIND eye-tech-solutions, Germany) performed by a single surgeon (VD) in a single center. The dataset includes 84 eyes of 47 patients, 37 of them using bilateral data. The corneal measurements were performed with an anterior segment optical coherence tomographer (MS-39, CSO, Italy). To compute the EOZ, an advanced automated method has been devised to define the boundaries of the treatment zone associated with the lenticule extracted from the cornea. The delineation of the corrected area is based on analyzing the disparities between postoperative and preoperative maps of several corneal metrics. This is achieved by identifying the minimal crossing point along each half meridian. Here, tangential anterior curvature was analyzed as corneal metric.
Results :
The clinical data indicated a POZ of 7.20 ± 0.29 mm [6.5 mm to 7.5 mm]. The calculated EOZ diameter was 6.56 ± 0.46 mm [5.25 mm to 7.51 mm], showing a linear dependency on the POZ. On average, the EOZ was 0.64 ± 0.32 mm smaller than the POZ, reflecting a reduction of approximately 9 % for the EOZ.
Conclusions :
The observed phenomenon of a smaller EOZ compared to the POZ aligns with findings reported in existing literature and corresponds to outcomes observed with other femtosecond laser systems used in corneal lens extraction treatments. The developed fully automated method for calculation of the EOZ provides a reliable and objective way to determine the size of a lenticule of tissue extracted from a cornea and can be applied to any topo- or tomographic derived metric.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.