Author: Danilo Andrade de Jesus, Wrocław University of Technology

Optical Coherence Tomography (OCT) has become a popular instrument to analyze the anterior segment of the eye. It is particularly attractive due its capability to provide, in real time, cross sectional images of tissue structure in situ. Interferometry, the measurement technique on which OCT is based, gives rise to speckle, which has been considered a form of noise that degrades the quality of the OCT image. In fact, speckle can also be signal-carrying and be used to infer about the properties of the tissue, as it has been done in ultrasound.

 Therefore, we have been trying to assess the corneal biomechanical properties modelling the corneal speckle from Optical Coherence Tomography. In order to achieve such goal, multiple mathematical statistical models have been used to fit the corneal backscattering data and the parameters of competing models were calculated using maximum likelihood estimation. The influence of choosing different regions of interest has also been into account. The applicability of the best model was tested analyzing corneal speckle statistics of subjects with different ages. In addition, variation of the corneal backscattering on subjects with induced corneal edema was tracked.

 Generalized Gamma Distribution has proven so far, to be the best model to fit the OCT corneal speckle. Its scaling and two shape parameters have shown to be sensitive to the variation of corneal backscattering properties. Differences among people with different ages was observed, showing the possibility to access corneal age-related changes using OCT corneal envelope statistics. Similar results were obtained for subjects with induced corneal edema showing that corneal backscattering statistics can also be used to track corneal biomechanical properties.

So far, we have seen that Generalized Gamma distribution can be used to fit the corneal speckle and may have a great potential to be a helpful complement to evaluate the structure and elastic properties of the cornea in-vivo. The results of this study will be presented on the Annual meeting of the Association for Research in Vision and Ophthalmology in Seattle, 1-5 May, 2016.