Visualizing Structure and Vascular Interactions: Macular Nonperfusion in Three Capillary Plexuses

Abstract

Background and objective: To assess the relationship between retinal vascular and structural changes in the superficial, middle, and deep capillary plexuses (SCP, MCP, DCP) using optical coherence tomography angiography (OCTA) and en face OCT.

Patients and methods: Patients with diabetic retinopathy were imaged using the Cirrus HD-OCT with AngioPlex. Using manual segmentation of the retinal layers, the authors compared OCTA to en face OCT images to examine corresponding patterns in each of the three capillary plexuses.

Results: Areas of decreased perfusion and capillary dropout on OCTA were found to be associated with three corresponding lesions on en face OCT: hyporeflectivity, cystic edema, and hard exudates. Vascular changes in individual capillary plexuses corresponded with structural changes in their respective perfused retinal layers.

Conclusions: Using manual segmentation on OCTA, the authors provide a framework to visualize the relationship between vascular pathology on OCTA and structural changes on en face OCT within specific capillary plexuses. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:e182-e190.].

Figure 1.

Optical coherence tomography angiography segmentation used to visualize the three capillary plexuses. (A) The superficial capillary plexus (SCP) was set by adjusting the preset superficial plexus window such that the boundaries were set at the preset internal limiting membrane to 55 μm above the inner plexiform layer (IPL). The SCP boundaries thus encompassed the nerve fiber layer, ganglion cell layer, and IPL. (B) The middle capillary plexus (MCP) was established by adjusting the preset deep plexus by setting the boundaries to 55 μm and 6 μm above the IPL, thus capturing the inner nuclear layer. Projection removal included in the machine software was applied to remove projection artifacts from vessels that lie superficially. (C) The deep capillary plexus (DCP) was established by adjusting the preset deep plexus by setting the boundaries to 6 μm above to 20 μm below the IPL, capturing the outer plexiform layer.

Figure 2.

Area of hyporeflectivity corresponding to decreased capillary perfusion in diabetic retinopathy. A to C represent the three capillary plexuses of an eye in a patient with diabetic retinopathy. For each plexus, the optical coherence tomography angiogram (OCTA) is shown along with the corresponding retinal tissue on structural en face OCT. The B-scan shows the segmented layers on cross-section used to image each capillary plexus. Each column shows a composite image in the last row with OCTA flow in yellow, areas of hyporeflectivity in blue, and areas devoid of flow in pink. (A) The superficial capillary plexus (SCP) shows healthy retinal vasculature with an appropriate area devoid of flow in the foveal avascular zone (FAZ). (B) The middle capillary plexus (MCP) shows areas of decreased perfusion highlighted by the blue circle around an area of capillary thinning with corresponding area of hyporeflectivity on structural en face OCT. On the composite image, the area of blue matches the area of capillary thinning to hyporeflectivity. (C) The deep capillary plexus (DCP) does not show the same area of hyporeflectivity as the MCP, with an expected area of avascularity in the FAZ.

Figure 3.

Areas of cystoid macular edema corresponding to capillary dropout in diabetic retinopathy. A to C represent the three capillary plexuses of an eye in a patient with diabetic retinopathy. For each plexus, the optical coherence tomography angiography (OCTA) is shown along with the corresponding retinal tissue shown on structural en face OCT. The B-scan shows the segmented layers on cross-section used to image each capillary plexus. Each column shows a composite image in the last row with OCTA flow in yellow, areas of hyporeflectivity in blue, and areas devoid of flow in pink. (A) The superficial capillary plexus (SCP) shows a black area devoid of flow highlighted by the pink circle. On the structural en face OCT, there is a corresponding area of black reflecting an area of edema. In the composite image, the area of capillary dropout corresponds to the black area on OCT. (B) The middle capillary plexus (MCP) similarly shows a different area of capillary dropout, with pockets of edema shown on structural OCT again highlighted by a pink circle. The areas of edema again correspond to areas devoid of flow in the composite image. (C) The deep capillary plexus (DCP) does not show distinct areas of edema but rather shows projection artifacts of the edema in the more superficial MCP and SCP.

Figure 4.

Area of hard exudates corresponding to decreased capillary perfusion in diabetic retinopathy. A to C represent the three capillary plexuses of an eye in a patient with diabetic retinopathy. For each plexus, the optical coherence tomography (OCT) angiogram is shown along with the corresponding retinal tissue shown on structural en face OCT. The B-scan shows the segmented layers on cross-section used to image each capillary plexus. Each column shows a composite image in the last row with OCTA flow in yellow, areas of hyporeflectivity in blue, and areas devoid of flow in pink. A and B show the superficial and middle capillary plexuses (SCP and MCP), respectively. C shows the deep capillary plexus (DCP) with areas of hyperreflectivity in the structural OCT representing hard exudates. This area of hard exudates, highlighted by a green circle, corresponds to an area of decreased capillary perfusion in the angiogram. In the composite image, the hard exudates, shown in white, are shown to reside in an area with decreased capillary perfusion.