New perspectives in retinal imaging - angio OCT

Abstract

In the last few years, structural and functional optical coherence tomography (OCT) technology has seen new and revolutionary developments. The most important of all is OCT angiography (Angio-OCT). Angio-OCT already plays an important role in clinical ophthalmology as a new, non invasive and dyeless diagnostic tool, which serves as an adjunct to, or even a replacement for fluorescein and indocyanine green (ICG) angiographies. Angio-OCT brings multiple technical and clinical improvements in the study of retinal diseases, glaucoma, and optic nerve disorders. It enables rapid, high-resolution, detailed images of large retinal vessels and capillary networks in seconds by using a strategy called "motion contrast", as opposed to revealing detailed images of large retinal vessels and capillary networks in seconds by using a strategy called "motion contrast" as opposed to the minutes required in conventional fluorescein angiography. These images are uniquely three-dimensional and allow an isolated study of individual capillary beds at different depths of the retina.

Keywords: angio-OCT; choroidal neovascularization; dyeless; optical coherence tomograph angiography.

Fig. 1

OCT Angiogram (Angiovue) (A) Full-thickness (internal limiting membrane to Bruch’s membrane) 3 x 3 mm. (B) Full-thickness 6 x 6 mm. (C) Full-thickness 8 x 8 mm. (D) Fluorescein angiography 8 x 8 mm. Less capil- lary detail than A-C

Fig. 2

OCTA image, 3 mm x 3 mm, of a normal eye. Full thick- ness OCT angiogram and cor- responding OCT B scan of the internal limiting membrane to Bruch’s membrane (A). OCTA of the inner retina (B), middle retina (C), outer retina (D), and choriocapillaris (E). OCTA at the optic nerve showing the radial peripapillary vascular network (F)

Fig. 3

Quantification of the inner retinal blood flow in nonproliferative diabetic retinopathy with macular edema. Fluorescein angiography (Left) shows defined foveal avascular zone (FAZ) as the area inside white dashed line, parafoveal region between white and blue dashed lines, and perifoveal zone between blue and green dashed lines. Enlargement of the FAZ is shown extending into parafoveal region (Middle). Scattered areas of macular nonperfusion are colored blue and presented on the 6x6 mm OCT angiogram (Right)

Fig. 4

Top row shows an example of a healthy eye and bottom row a glaucomatous eye. In comparison to the healthy eye (B), en face OCT angiogram of glaucomatous eye (F) shows a reduced density of the peripapillary mi- crovasculature network. Patches of nonperfusion in glaucoma correlated well with the locations of retinal nerve fiber layer thickness maps deficits (G) and visual field loss (H)

Fig. 5

The type I CNV is identified by OCT angiography (C), but it is not well defined by fundus photography (A) or fluoresce- in angiography (B). The black square out- lines the areas shown on the angiograms. The CNV area is shown on the en face col- or-coded OCT angiogram (C). The dashed yellow line shows the location of the OCT cross section (D). The analysis of the yel- low highlighted CNV flow reveals that CNV is predominantly under the retinal pigment epithelium