Proceedings Article | 19 February 2020
Proc. SPIE. 11218, Ophthalmic Technologies XXX
KEYWORDS: Image segmentation, Image processing, Image filtering, Eye, Gaussian filters, Edge detection, Optical coherence tomography, Angiography, Diagnostics, Retina
The Foveal Avascular Zone (FAZ) is of clinical importance since the vascular arrangement around the fovea changes with disease and refractive state of the eye. Therefore, it is important to segment and quantify the FAZs accurately. Here we provide a new methodology for this measurement. Eighty normal fundus images of dimensions 420x420 pixels corresponding to 6mm x 6mm were used in this study. Each fundus image was manually segmented by a clinical expert (ground truth), the new methodology and an existing technique provided by the image acquisition device (Cirrus 5000 Carl Zeiss Meditec Inc., Dublin, CA). The images were first processed by a Difference of Gaussian (DoG) filter iteratively 25 times after being complemented. This is followed by a Prewitt edge detection and repeated image dilation at angles of 0,45 and 90 degrees. Image closure was then applied followed by noise and small object removal which resulted in the segmented boundary. For deeper insight into shape change, besides the diameter of the FAZ other parameters - eccentricity, perimeter, major axis, minor axis, incircle, circumcircle, Fmin, Fmax, tortuosity, vessel diameter index and vessel avascular density - were calculated. The mean diameter by manual segmentation was 673.04 ± 86.92 μm compared to 688.42 ± 72.18 μm by our technique. The corresponding value generated by the instrument was 623.60 ± 121.50 μm. This technique shows considerable improvement in accuracy (the mean value as well as the standard deviation) when compared to system segmentation and the ground truth. These aspects will be discussed in the paper.
