Measurement of Choroidal Neovascular Area in Age-Related Macular Degeneration using Modified Otsu’s Thresholding Method

Abstract

Introduction: Age-related Macular Degeneration (AMD) is one of the most important causes of irreversible <br/>blindness in the developed world and prevents the affected person from performing simple tasks such as <br/>reading, driving and facial recognition. In the AMD, new blood vessels grow underneath the retina in a <br/>process called choroidal neovascularisation (CNV). There is much interest in the quantification of the <br/>angiographic features of CNV, as these parameters are used as markers for monitoring the response to CNV <br/>treatment. To date, the techniques used in angiographic analysis are based on subjective interpretation by <br/>experienced clinicians. The goal of the present study was to propose an automatic algorithm for determining <br/>the extent of CNV. <br/>Materials and Methods: The proposed algorithm was used to analyze indocyanine angiograms of 12 <br/>patients with CNV. The angiograms were acquired by a confocal scanning laser ophthalmoscope. The <br/>algorithm included an adaptive Wiener filtering technique, a top-hat morphology method and a new <br/>thresholding technique based on a modification of Otsu's method. The area of each lesion was obtained and <br/>compared with a subjective evaluation of CNV. Finally, each area was expressed in square millimeters by <br/>making a cylindrical tube filled with indocyanine green. <br/>Results: The CNV area was determined by the proposed algorithm and an observer. No significant <br/>differences were observed between the two data sets (p>0.05). <br/>Discussion and conclusion: This study demonstrates that the proposed algorithm based on a modification of <br/>Otsu's method can be used to measure the area of CNV.