Most commercially-available systems are based on split-spectrum amplitude-decorrelation algorithm (SSADA), which detects red blood cell movement independently from its direction. Of the parameters that can be analysed, peripapillary angioflow density (the perfusion area expressed in the percentage of the total examined peripapillary area) and whole image angioflow density (the perfusion area expressed in the percentage of the total examined image area) provide the most useful information in glaucoma.
In OCTA, perfusion of the different retinal layers are measured separately on the same image. For diseases involving the retinal nerve fibre layer, such as glaucoma, OCTA of the radial peripapillary capillaries layer provides the most useful information.
Recently, it was shown that the diagnostic accuracy of peripapillary and whole image angioflow density in differentiating between glaucoma eyes and normal eyes was similar to that of retinal nerve fibre layer thickness (RNFLT) measurements.1 In the radial peripapillary capillaries layer (i.e., the retinal nerve fibre layer), peripapillary angioflow density showed strong correlation with RNFLT.2
The measurements have favourable reproducibility that is independent of the disease severity, thus measurements made in advanced glaucoma are no less reliable than those made on healthy eyes.2 The sector OCTA parameters show a strong relationship with the sensitivity and defect values of the spatially corresponding visual field areas, so future research may address the focal perfusion-function relationship, similarly to that of the focal structure-function relationship.
It was also recently shown that a topical medical pressure reduction of at least 50% induced a significant increase in the peripapillary angioflow density in untreated high-pressure open-angle glaucoma and ocular hypertension.3 Thus, the relationship between IOP reduction and increase of peripapillary perfusion may be a new area in OCTA research.