16/11/2015

Author: Alejandra Consejo, Wrocław University of Technology

The aim of this work, which hopefully will be presented in the IEEE International Symposium on Biomedical Imaging (2016, Prague), was to develop a curvature based estimator for the location of limbus, defined as the junction between cornea and sclera. Data collected from a simulated example, an artificial bi-sphere test surface and a real eye is used to validate the method. Since curvature calculation requires double differentiation of the surface under analysis and differentiation calculation greatly amplify any noise present in the data, applying regularization techniques is needed in order to control the noise effect. Different regularization techniques are tested, resulting in Deriche filtering operators that found to be the most applicable. Determining the change in the curvature of the surface of the anterior part of the eye is possible using Deriche filtering operators. This regularization technique provides accurate results for limbal demarcation. The proposed method is applied successfully on the bisphere test surface as the figure shows. The radius obtained has 0.98 % relative error. The study suggest that the shape of the limbus in the human eye is not symmetric – an important consideration in contact lens design.

Figure. Change in the curvature detection for the artificial bi-sphere. Overlapping blue asterisks indicate the registered curvature change in each meridian and yellow line indicates the fit of a circle of the points.