António Luís Correia's research while affiliated with Association for Innovation and Biomedical Research on Light and Image and other places

Purpose To identify the changes at the cellular level responsible for the differences seen in OCT scans of DME patients. Methods Cirrus HD‐OCT (Carl Zeiss Meditec, Dublin, CA, USA) scans of DME eyes (12 eyes of 8 patients: 68.9±7.5 yrs) and healthy control (HC) eyes (12 eyes of 11 controls: 63.0±3.6 yrs) were acquired from our database. The ONL was segmented by a human grader (AC) and each segmentation was aligned to its upper boundary, averaged into an A‐scan and then normalized by the intensity at the RPE to discard the effect of media opacities. To understand the significant differences found between the profiles of DME and HC, a Monte Carlo method for simulating light scattering with a model of the ONL was implemented. The inputs for the method are calculated using Mie theory by assuming that the ONL may be modelled as a homogeneous medium filled with nuclei. Changes in each model parameter (e.g. nucleus' size) were tested and compared with the measured profile to identify which cellular change could best reproduce the OCT differences found between HC and DME patients. Moreover, the DME group was divided into those without significant visible changes and those with increased ONL volume. Results The simulation method successfully reproduced the differences observed between the HC and DME groups. For the DME cases with increased volume, it was possible to match the simulated and acquired profiles by using the measured increase in ONL thickness. In the DME case with no significant changes, it was necessary to increase only the nucleus size to be able to reproduce the measured profiles. Conclusion The method proposed is capable of reproducing the reflectivity changes measured on OCT scans of the ONL of DME eyes and to justify these at the subcellular level.

Optical coherence tomography (OCT) scans were acquired from healthy controls and patients with diabetic macular edema (DME), a common complication of diabetes characterized by increased retinal thickness due to fluid accumulation. The collected OCT data was divided into three distinct groups: healthy subjects, DME patients with significantly increased outer nuclear layer (ONL) thickness and DME patients without visible changes in the ONL. For each group, the ONL was segmented and processed, yielding a representative A-scan. Using reference values for the physical and optical characteristics of the healthy human retina, we used a Monte Carlo method with a model for the ONL to simulate an A-scan for each group and compare it to the real OCT data. This allowed to identify which alterations in the cellular characteristics are responsible for the changes observed in the OCT scans of the diseased groups.

Optical Coherence Tomography, OCT, is a relatively recent imaging technique that allows high resolution imaging of the retina. It relies in certain optical characteristics of light to provide information of the eye fundus, facilitating the diagnosis of certain eye pathologies. Our goal is to build a mathematical model that describes the electromagnetic wave's propagation through the eye's structures, using Maxwell's equations, in order to create a virtual OCT scan. With this virtual exam, we will be able to test different characteristics of the medium and assess their effect on the final image.