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

Age-related Macular Degeneration (AMD) is one of the most important causes of irreversible blindness in the developed world and prevents the affected person from performing simple tasks such as reading, driving and facial recognition. In the AMD, new blood vessels grow underneath the retina in a process called choroidal neovascularisation (CNV). There is much interest in the quantification of the angiographic features of CNV, as these parameters are used as markers for monitoring the response to CNV treatment. To date, the techniques used in angiographic analysis are based on subjective interpretation by experienced clinicians. The goal of the present study was to propose an automatic algorithm for determining the extent of CNV.

The proposed algorithm was used to analyze indocyanine angiograms of 12 patients with CNV. The angiograms were acquired by a confocal scanning laser ophthalmoscope. The algorithm included an adaptive Wiener filtering technique, a top-hat morphology method and a new thresholding technique based on a modification of Otsu’s method. The area of each lesion was obtained and compared with a subjective evaluation of CNV. Finally, each area was expressed in square millimeters by making a cylindrical tube filled with indocyanine green.

The CNV area was determined by the proposed algorithm and an observer. No significant differences were observed between the two data sets (p>0.05). Discussion and

This study demonstrates that the proposed algorithm based on a modification of Otsu’s method can be used to measure the area of CNV.