9.4  Optical Coherence Tomography Angiography (OCT-A)

Optical coherence tomography angiography (OCT-A) has emerged as a non-invasive technique for imaging the microvasculature of the retina and the choroid. It utilises laser light reflectance off the surface of moving red blood cells to accurately depict vessels through different segments, thus eliminating the need for intravascular dyes. OCT-A produces images that can be segmented into different levels, e.g.: the superficial retinal plexus, the deep retinal plexus, the outer retina and the choriocapillaris.

The main advantages of OCT-A over conventional fluorescein angiography include its non-invasiveness and the shorter acquisition times. Limitations include artefacts such as projection artefact.

In OCT-A, diseases manifest as the abnormal presence of flow (neovascularisation), anomalous vessel geometry (dilated vessels, aneurysms) or the absence of flow (non-perfusion/capillary dropout). It does not visualise leakage or polyps accurately.

Clinical Applications

OCT-A is increasingly being utilised to assess retinal and optic nerve disorders.

Retina

  • Diabetic retinopathy – identifying the foveal avascular zone, microaneurysms and neovascular complexes
  • CNV analysis in age-related macular degeneration, central serous chorioretinopathy, myopic CNV, macular telangiectasia and uveitic CNV
  • Vascular occlusions – evaluation of nonperfused areas and the integrity of the superficial and deep plexus. The preservation of the deep vasculature has been associated with better visual outcomes

Optic Nerve Disorders

  • Glaucoma – may enable pre-perimetric detection of glaucomatous damage by assessing for attenuated peripapillary and macular vessel density.
  • Differentiating papilledema from disc drusen
Figure 9.4.1 OCT-A displaying an Area of Type 1 (sub-RPE) NeovascularisationSsecondary to Central Serous Chorioretinopathy

Figure 9.4.1
OCT-A displaying an Area of Type 1 (sub-RPE) Neovascularisation Secondary to Central Serous Chorioretinopathy

Note the vascular loop of medium and large vessels in the outer retina to choriocapillaris (ORCC)

          

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