Researchers recently found that cilioretinal arteries have a major impact on some retinal vessel densities (VD)—a finding they say should be taken into consideration when analyzing quantitative optical coherence tomography angiography (OCT-A) parameters in scientific and clinical applications.

The study included 83 eyes of 83 patients (28 male, 55 female). The macula was imaged with a 3x3mm scan and the optic nerve head (ONH) with a 4.5x4.5mm scan by the same expert examiner in a single location. The researchers screened OCT-A images for presence of cilioretinal arteries. They categorized small vessels as those that did not leave a 4.5mm ring around the ONH, medium-sized vessels as those that didn’t reach the fovea and large vessels as those located temporally to the fovea.

They found cilioretinal arteries in 31 eyes (37.3%), all of which arose from the temporal margin of the optic disc. In these eyes, the researchers noted that VD was significantly lower in the ONH but higher in the peripapillary capillary network and macular superficial capillary plexus compared with eyes without cilioretinal arteries. Sizes of vessels were as follows: 48% were small, 38% were medium and 16% were large.

“The effect of cilioretinal vessels on retinal microcirculation in terms of a peripapillary increase in VD might have different reasons: First, the flow rate and vascular perfusion pressure through retinal vessels is significantly lower than through the choroid vasculature such as in cilioretinal arteries,” the researchers explained in their paper. “The higher flow rate could lead to an increase in VD.”

“Second, autoregulatory processes exist in retinal blood vessels, but only a limited degree of autoregulation is present in choroidal blood vasculature such as in cilioretinal arteries,” they continued. “Moderate elevation of intraocular pressure (IOP) or moderate changes in blood pressure don’t markedly affect the retinal blood circulation.”

They also noted that in contrast, choroidal blood flow increases with higher blood pressure and decreases with higher IOP. “Intraday changes in IOP and blood pressure are likely to lead to a change in perfusion of the cilioretinal artery,” they wrote. “It’s imaginable that the increased VD in eyes with cilioretinal arteries could be a compensatory response of the retinal vasculature to maintain retinal oxygen saturation during diurnal IOP and blood pressure fluctuations. It’s been hypothesized that cilioretinal arteries play a protective role in retinal diseases due to their additional blood supply to the macula.”

They concluded that cilioretinal arteries must be considered when analyzing OCT-A metrics, “especially when analyzing the ONH to avoid a biased statistical analysis.”

Diener R, Leclaire MD, Eckardt F, et al. Cilioretinal arteries influence optic nerve head, peripapillary and macular vessel densities in healthy eyes: an optical coherence tomography angiography study. Retina. May 3, 2021. [Epub ahead of print].