Detection of foveal avascular zone in colour retinal fundus images

Abstract

Diabetic retinopathy (DR) is a complication of retinal related common micro vascular disease occurred in diabetic patients. It is the one of the major causes of adult blindness in the worldwide. DR is indicated by the presence of hard exudates, soft exudates, haemorrhages, the growth of new blood vessels and foveal avascular zone (FAZ) enlargement. The objective of this work is to detect FAZ area in the colour retinal fundus images. In retinal fundus images, FAZ is located in the centre of macula, which is usually capillary-free. The detection of FAZ is an important step in the assessment of retinal images for visual related pathology detection. Retinal images are taken from Messidor database consisting of 59 retinal images. The proposed method has four main steps, i.e. pre-processing, blood vessels extraction, FAZ detection, and validation test. In the pre-processing step, morphological operation followed by contrast stretching is used to enhance and improve image quality. In other hand, matched filter and local entropy thresholding are applied to extract retinal blood vessels. FAZ area is detected by connecting retinal vessel endpoints. Finally, validation test is conducted by calculating the correlation between polygon area as detected FAZ by proposed method and circular area as labelled FAZ by ophthalmologists. The result achieves the correlation coefficient of 0.912 indicating that the proposed method has significant correlation with the method of the ophthalmologists.