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Published on: February 18, 2022
The Influence of Magnification Correction on Macular Retinal/Choroidal Thickness and Vessel Density Measurements
Zengrui Zhang1, Hao Wu1, Yining Zeng1
1Chengdu university of TCM, No.37 Twelve Bridge Road, Chengdu, 610075, Sichuan, China; Eye College of Chengdu University of TCM, No.37 Twelve Bridge Road, Chengdu, 610075, Sichuan, China; Ineye Hospital of Chengdu University of TCM, No. 8 Xinghui West Road, Jinniu District, Chengdu City, Sichuan Province, China; Eye Health with Traditional Chinese Medicine Key Laboratory of Sichuan Province.
Background:
Transverse macular measurements from optical coherence tomography angiography (OCTA) depend on ocular magnification, which varies with axial length (AL); in growing children, whether correcting for magnification alters macular thickness and vessel-density measurements enough to matter clinically is unclear, and no anchor-based clinical threshold exists.
Methods:
In this cross-sectional study, retinal and choroidal thickness (RT, ChT) and retinal and choroidal vessel density (RVD, CVD) -each in the central fovea, parafovea, perifovea and whole-grid average (16 parameters) -were measured before and after magnification correction in 339 children and adolescents aged 4-17 years (central 6 × 6 mm macula, swept-source OCTA [SS - OCTA]); vessel length density (VLD) and matched superficial retinal vessel density (SRVD) were also compared. Clinical relevance was tested against a distribution-based 0.5 × standard deviation (SD) threshold by equivalence testing, and the correction difference was modelled across AL.
Results:
Correction produced statistically detectable changes in many parameters, but the mean difference for all 16 parameters lay within ±0.5 × SD (population-level equivalence). Only perifoveal and average RT crossed the threshold, at the extremes of AL (< 21.4 or > 26.6 mm and > 27.7 mm, respectively); choroidal thickness and areal vessel density were essentially unaffected (relative change ≤ 0.3%). In contrast, VLD scaled inversely with the magnification factor and crossed the threshold within the observed range (AL < 22.3 or > 25.7 mm; 11.5% of eyes), whereas SRVD crossed nowhere. The AL-RT association weakened after correction; vessel density related mainly to age.
Conclusion:
In this pediatric cohort, magnification correction was clinically important chiefly for retinal thickness in very short or very long eyes and for vessel length density outside AL 22.3-25.7 mm; choroidal thickness and areal vessel density were little affected. A parameter's need for correction is thus set by its dimensions. Age should also be considered when interpreting macular microvasculature in children.
