April 2016
Volume 57, Issue 4
Open Access
Letters to the Editor  |   April 2016
Quantification of Vessel Density in Retinal Optical Coherence Tomography Angiography Images Using Local Fractal Dimension
Author Affiliations & Notes
  • Rong Hu
    Department of Ophthalmology of the Second Xiangya Hospital Central South University, Changsha, China
  • Chun Ding
    Department of Ophthalmology of the Second Xiangya Hospital Central South University, Changsha, China
Investigative Ophthalmology & Visual Science April 2016, Vol.57, 2262. doi:10.1167/iovs.16-19256
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      Rong Hu, Chun Ding; Quantification of Vessel Density in Retinal Optical Coherence Tomography Angiography Images Using Local Fractal Dimension. Invest. Ophthalmol. Vis. Sci. 2016;57(4):2262. doi: 10.1167/iovs.16-19256.

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      © ARVO (1962-2015); The Authors (2016-present)

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We read with interest the article by Gadde and colleagues1 on quantifying vessel density and the foveal avascular zone (FAZ) area in optical coherence tomography angiography (OCTA) images using a fully automated local fractal dimension method. The authors concluded that this novel method can calculate retinal vessel density and the FAZ area. They also contended that retinal vessel density was not correlated with age and that the inferior zone of retinal vessel density is largest in the parafoveal region. We congratulate and applaud their interesting and important work on this topic; however, we have one question for the authors regarding intra-and interobserver variation and the reproducibility of the OCTA examination. 
It is well acknowledged that a new diagnostic tool should be validated regarding its reliability and reproducibility before its application. The previous methodologies for measuring ocular parameters such as retinal nerve fiber layer thickness,2 choroidal thickness,3 and retinal oxygen saturation4 all have been tested for their reliability and reproducibility. As far as we are concerned, when the subjects underwent imaging with the OCTA system (AngioVue; OptoVue, Fremont, CA, USA), because of the relative long duration of the examination and unstable fixation, some subjects acquired low-quality images. If the subjects had repeated instances of unstable fixation, the image would appear with white ambiguous lines. The analysis software would mistake these white ambiguous lines for blood vessels and would overestimate the retinal vessel density. Therefore, intra- and interobserver variation would, in theory, be relatively large. We wonder why the authors did not perform a reproducibility analysis to prove the stability of the OCTA system examination. If such an analysis had been performed and intra- and interobserver variation exceeded a certain percent, the results of this study might have been shown to be unreliable. 
Acknowledgments
Supported by the National Natural Science Foundation of China (No. 81300758). The authors alone are responsible for the content and writing of the paper. 
References
Gadde SG, Anegondi N, Bhanushali D, et al. Quantification of vessel density in retinal optical coherence tomography angiography images using local fractal dimension. Invest Ophthalmol Vis Sci. 2016; 57: 246–252.
Lee K, Sonka M, Kwon YH, Garvin MK, Abramoff MD. Adjustment of the retinal angle in SD-OCT of glaucomatous eyes provides better intervisit reproducibility of peripapillary RNFL thickness. Invest Ophthalmol Vis Sci. 2013; 54: 4808–4812.
Ho J, Branchini L, Regatieri C, Krishnan C, Fujimoto JG, Duker JS. Analysis of normal peripapillary choroidal thickness via spectral domain optical coherence tomography. Ophthalmology. 2011; 118: 2001–2007.
Man RE, Kawasaki R, Wu Z, et al. Reliability and reproducibility of retinal oxygen saturation measurements using a predefined peri-papillary annulus. Acta Ophthalmol. 2013; 91: e590–e594.
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