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Invest Ophthalmol Vis Sci. 2017 Jun 1;58(7):3065-3072. doi: 10.1167/iovs.17-21551.

Axial Length Variation Impacts on Superficial Retinal Vessel Density and Foveal Avascular Zone Area Measurements Using Optical Coherence Tomography Angiography.

Author information

1
Centre for Ophthalmology and Visual Science, The University of Western Australia, Perth, Western Australia, Australia 2Lions Eye Institute, Perth, Western Australia, Australia.
2
Optical+Biomedical Engineering Laboratory, School of Electrical, Electronic & Computer Engineering, The University of Western Australia, Perth, Western Australia, Australia.
3
College of Optical Science and Engineering, Zhejiang University, Hangzhou, China.
4
Department of Ophthalmology, Sir Charles Gairdner Hospital, Perth, Western Australia, Australia.
5
Centre for Ophthalmology and Visual Science, The University of Western Australia, Perth, Western Australia, Australia.
6
Optical+Biomedical Engineering Laboratory, School of Electrical, Electronic & Computer Engineering, The University of Western Australia, Perth, Western Australia, Australia 6Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, Perth, Western Australia, Australia.
7
Centre for Ophthalmology and Visual Science, The University of Western Australia, Perth, Western Australia, Australia 2Lions Eye Institute, Perth, Western Australia, Australia 7Department of Ophthalmology, Royal Perth Hospital, Perth, Western Australia, Australia.

Abstract

Purpose:

To evaluate the impact of image magnification correction on superficial retinal vessel density (SRVD) and foveal avascular zone area (FAZA) measurements using optical coherence tomography angiography (OCTA).

Methods:

Participants with healthy retinas were recruited for ocular biometry, refraction, and RTVue XR Avanti OCTA imaging with the 3 × 3-mm protocol. The foveal and parafoveal SRVD and FAZA were quantified with custom software before and after correction for magnification error using the Littman and the modified Bennett formulae. Relative changes between corrected and uncorrected SRVD and FAZA were calculated.

Results:

Forty subjects were enrolled and the median (range) age of the participants was 30 (18-74) years. The mean (range) spherical equivalent refractive error was -1.65 (-8.00 to +4.88) diopters and mean (range) axial length was 24.42 mm (21.27-28.85). Images from 13 eyes were excluded due to poor image quality leaving 67 for analysis. Relative changes in foveal and parafoveal SRVD and FAZA after correction ranged from -20% to +10%, -3% to +2%, and -20% to +51%, respectively. Image size correction in measurements of foveal SRVD and FAZA was greater than 5% in 51% and 74% of eyes, respectively. In contrast, 100% of eyes had less than 5% correction in measurements of parafoveal SRVD.

Conclusions:

Ocular biometry should be performed with OCTA to correct image magnification error induced by axial length variation. We advise caution when interpreting interocular and interindividual comparisons of SRVD and FAZA derived from OCTA without image size correction.

PMID:
28622398
DOI:
10.1167/iovs.17-21551
[Indexed for MEDLINE]

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