Abstract
Purpose :
Capillary non-perfusion due to diabetic macular ischemia (DMI) affects both the foveal and parafoveal photoreceptors. While best corrected visual acuity (BCVA) is a foveal cone function, low luminance visual acuity is thought to be also influenced by parafoveal rod photoreceptors. In clinical trials on DMI, BCVA, LLVA and FAZ area are considered key outcome measures. Many OCTA devices have automated FAZ metrics. However, due to the irregularity, motion artefacts, segmentation artefacts, decentration, undetected capillary non-perfusion, and suspended scattering particles in motion, we need to manually delineate the FAZ. We investigated the correlation of BCVA and LLVA with automated and manual FAZ areas.
Methods :
In this prospective observational study on DMI in patients with stable treated proliferative Retinopathy and severe non-proliferative DR, DMI was defined by automated metrics of OCTA as an irregular foveal avascular zone (FAZ) area ≥ 0.5 mm2 or a smaller FAZ area with parafoveal capillary dropout in at least one quadrant. Automated FAZ values and manually corrected FAZ values were then correlated with the BCVA and LLVA. If both eyes were eligible, eye with better image quality was taken as study eye.
Results :
Forty-five of the 48 patients recruited into the study had gradable scans and were eligible for the analysis. The mean BCVA and LLVA were 77.38+/-7.38 and 69.62+/-8.19 ETDRS letters respectively. Mean manually corrected FAZ area was significantly larger at 0.71+/-0.38 mm2 compared to automated FAZ area of 0.55+/-0.29mm2 (p-value<0.01) with proportional bias on Bland-Altman plot(figure 1). BCVA showed a poor negative correlation with both manually corrected(figure 2) and automated FAZ (-0.29, p-value= 0.06 and -0.24, p-value =0.11). Similarly, LLVA also showed poor correlation with both FAZ metrics. The correlation with corrected FAZ was -0.006 (p-value=0.97) and automated FAZ 0.015 (p value-0.92).
Conclusions :
This study provides evidence that in DMI, despite differences in FAZ area between manually graded and automated graded FAZ, they both showed poor correlation with BCVA and LLVA, substantiating that FAZ area changes are not a surrogate marker for visual function in DMI.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.