During this period, I focused mainly on extracting as many features as possible from the available DR images, based on strict quality criteria (regarding inclusion of observations, power estimations and avoidance of statistical errors). Moreover, a suitable hybrid mixed model was introduced specific for the nature of my analysis which can be used when the independence of observations is violated in simple models where we include correlated data.
The fractality and lacunarity for the complexity of vascular trees has been introduced for which the skeletonised or segmented images are required. Multiple features are being tested for their significance and discriminative ability identifying patterns of changes when the vessels’ structure is changing.
New features include branch retinal equivalent, width-to-angle ratio, sum of squares of widths (which is continuosly differentiable and useful for minimising variance) and can be used in the cross section estimation which in turn is useful for the flow rate function. Centreline length to straight distance ration and the junction exponent calculated by the Branching coefficient and fractal (box-counting/hausdorf) dimention are among the other possible features.