Retinal vascular fractal dimension measurement and its influence from imaging variation: results of two segmentation methods.
OBJECTIVE
To assess the influences of imaging variation (different photographic angle) on the measurement of retinal vascular fractal dimension (D(f)), using two segmentation methods.


METHODS
Nonlinear orthogonal projection segmentation (International Retinal Imaging Software-Fractal, termed IRIS-Fractal) and curvature-based segmentation (Singapore Institute Vessel Assessment-Fractal, termed SIVA-Fractal) methods were used to measure D(f) and were assessed for their reproducibility in detecting retinal vessels of 30 stereoscopic pairs of optic disc color images. Each pair was taken from the same eye with slightly different angles of incidence. Each photograph of the pairs had subtle variations in brightness between areas temporal and nasal to the optic disc.


RESULTS
Intragrader reproducibility of D(f) measurement was similar (intraclass correlation 0.81 and 0.96, respectively) for IRIS-Fractal and SIVA-Fractal. Within-image pair Pearson's correlation coefficients (r) of D(f) measurements were moderate for both methods (0.57 and 0.48, respectively).


CONCLUSIONS
Both nonlinear orthogonal projection and curvature-based retinal vessel segmentation methods were found to be sensitive to variations in image brightness, resulting from iris shadowing associated with different angle of photographic incidence.
Cosatto
Victoria Fay
VF
Centre for Eye Research Australia, Department of Ophthalmology, University of Sydney, Sydney, Australia.
Liew
Gerald
G
Rochtchina
Elena
E
Wainwright
Alan
A
Zhang
YongPing
Y
Hsu
Wynne
W
Lee
Mong Li
ML
Lau
Qiangfeng Peter
QP
Hamzah
Haslina H
HH
Mitchell
Paul
P
Wong
Tien Yin
TY
Wang
Jie Jin
JJ
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D017709:Fractals; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000098:blood supply*; D010781:Photography; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology*