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

Document Type: Original Paper

Authors

1 M.Sc. Student in Medical Physics, Tehran University of Medical Sciences, Tehran, Iran

2 Assistance Professor of Medical Physics and Biomedical Engineering Dept., Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, Tehran, Iran

3 Associate Professor of Medical Physics and Biomedical Engineering Department, Research Center for Science and Technology in Medicine, Tehran University of Medical Sciences, Tehran, Iran

4 Associate Professor, Ophthalmology Dept., Iran Eye Research Center, Iran University of Medical Sciences, Tehran, Iran

5 M.Sc. Student in Optometry, Iran University of Medical Sciences, Tehran, Iran

6 Assistance Professor, Ophthalmology Dept., Iran Eye Research Center, Iran University of Medical Sciences, Tehran, Iran

7 Fellowship, Ophthalmology Dept., Iran University of Medical Sciences, Tehran, Iran

Abstract

Introduction: 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. 
Materials  and  Methods:  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.  
Results:  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 conclusion: This study demonstrates that the proposed algorithm based on a modification of 
Otsu’s method can be used to measure the area of CNV. 

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