To analyze the effect of induced astigmatism on en-face spectral-domain optical coherence tomography angiography (SD-OCTA) quantitative metrics.
Prospective Cross-Over Study METHODS: Normal eyes without astigmatism and with 0.75, 1.75, and 2.75 diopters (D) of with-the-rule (WTR) astigmatism were imaged utilizing a 3x3mm scan pattern SD-OCTA CIRRUS 5000 HD-OCT with AngioPlex (Carl Zeiss Meditec, Dublin, CA, USA). Quantitative parameters including foveal avascular zone (FAZ) metrics, parafoveal vessel length density (VD), and perfusion density (PD) were corrected for magnification secondary to axial length and analyzed. Univariate linear regressions were performed within each eye to correlate quantitative metrics to level of induced astigmatic cylinder.
15 eyes (15 patients) were imaged. Every 1D increase in induced WTR astigmatism was associated with a statistically significant decrease in VD and PD within all ETDRS (Early Treatment Diabetic Retinopathy Study) inner-ring quadrants, however especially so nasally (VD: 0.63, p<0.001; PD: 0.0089, p = 0.001). For every 1D increase in induced astigmatism, the resulting decrease in the inner-ring superior quadrant was 12% greater for VD and 16% greater for PD versus the inferior quadrant; the resulting decrease in the inner-ring nasal quadrant was 40% greater for VD and 48% greater for PD versus the temporal quadrant.
Increasing levels of induced WTR astigmatism correlate with globally diminishing VD and PD, more symmetrically for vertical than horizontal quadrants, and most pronounced nasally. This may be due to a high prevalence of horizontally-oriented vessels nasally, and the horizontal optical defocus induced by WTR astigmatism.
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