Lateral Magnification Correction of Foveal Avascular Zone Area Important in OCT-A Imaging

Correcting lateral magnification when evaluating foveal avascular zone area (FAZA) is clinically important with respect to accurately quantifying optical coherence tomography-angiography (OCT-A) parameters, according to a study published in Ophthalmology Science. 

Researchers conducted an analysis of 504 healthy, young adults (mean age, 28.2 years, 261 women). They performed comprehensive eye examinations, axial length scans, and  macular OCT-A imaging on all patients. The team processed OCTA images of the combined superficial and deep retinal vessel plexuses through a custom program to obtain FAZA and vessel density in a 300-μm annulus surrounding the foveal avascular zone (FD-300). The custom software exported OCTA parameters with and without correction for lateral magnification. 

The report shows that the mean standard deviation (SD) of laterally corrected FAZA and FD-300 were 0.22 (0.10) mm² and 51.9 (3.2) %, respectively. In total, 55.6% of corrected FAZA showed a relative change higher than 5%, while all FD-300 changes after correction were within the 5% error margin in all eyes. The researchers reported good intraocular symmetry (mean OD-OS difference, 95% limits of agreement) in both FAZA (0.006, -0.077 to 0.118 mm²) and FD-300 (-0.05, -5.39 to 5.30 %). They noted significant negative relationships between central retinal thickness and FAZA (β = -0.0029) and between central retinal thickness and FD-300 (β = -0.044), with the associations influenced by inner retina.

Researchers stress that while correcting lateral magnification for FAZA is important, “adjusting for FD-300 may not be as critical clinically in young, healthy eyes.” They emphasize that “clinicians should strongly consider accounting for lateral magnification when evaluating FAZA.”

This study is limited by the narrow age range among participants.

Reference

Li Q, Gong P, Ho PH, et al. Evaluating distribution of foveal avascular zone parameters corrected by lateral magnification, and their associations with retinal thickness. Ophthalmol Sci. Published online March 1, 2022. doi:10.1016/j.xops.2022.100134