Impact of ocular magnification on retinal and choriocapillaris blood flow quantification in myopia with swept-source optical coherence tomography angiography

Yining Dai; Chen Xin; Qinqin Zhang; Zhongdi Chu; Hao Zhou; Xiao Zhou; Liya Qiao; Ruikang K Wang

doi:10.21037/qims-20-1011

Impact of ocular magnification on retinal and choriocapillaris blood flow quantification in myopia with swept-source optical coherence tomography angiography

Quant Imaging Med Surg. 2021 Mar;11(3):948-956. doi: 10.21037/qims-20-1011.

Authors

Yining Dai¹, Chen Xin², Qinqin Zhang¹, Zhongdi Chu¹, Hao Zhou¹, Xiao Zhou¹, Liya Qiao², Ruikang K Wang^{1

3}

Affiliations

¹ Department of Bioengineering, University of Washington, Seattle, WA, USA.
² Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
³ Department of Ophthalmology, University of Washington, Seattle, WA, USA.

Abstract

Background: To evaluate the impact of ocular magnification on retinal and choriocapillaris (CC) blood flow quantification in myopic eyes using swept-source optical coherence tomography angiography (SS-OCTA).

Methods: Subjects with myopia were recruited for comprehensive ophthalmic examination and SS-OCTA imaging with 6×6 mm² scanning protocol. Retinal vessel area density (RVAD), retinal vessel skeleton density (RVSD), and percentage of CC flow deficits (CC FD%) were quantified within a 5-mm-diameter circle centered on the fovea before and after magnification correction using the Littman and the modified Bennett formulae.

Results: Images from 28 myopic eyes were qualified for quantitative analyses including 12 eyes with non-high myopia (43%) and 16 eyes with high myopia (57%). The mean spherical equivalent (SE) refractive error was -8.18±4.58 diopters (D) and the mean axial length was 27.9±2.5 mm. The mean corrected RVAD was significantly lower than the uncorrected RVAD in all myopic eyes (0.51±0.02 vs. 0.52±0.02, P<0.001). The mean corrected RVSD was also significantly lower than the uncorrected RVSD in myopic eyes (0.13±0.01 vs. 0.15±0.00, P<0.001). In highly myopic eyes, the mean corrected CC FD% was significantly higher than the uncorrected CC FD% (14.9%±4.9% vs. 14.2%±4.5%, P=0.009). In non-highly myopic eyes, no statistically significant difference was observed between the corrected and uncorrected CC FD% measurements (11.7%±5.8% vs. 11.5%±5.8%, P=0.133).

Conclusions: Ocular magnification significantly affects the results of retinal and CC blood flow quantification with OCTA in myopic eyes. For accurate determination of the OCTA derived parameters in myopia, magnification correction should be taken into consideration.

Keywords: Optical coherence tomography angiography (OCTA); axial length; magnification error; myopia; quantitative analysis.