Optical Coherance Tomography Angiography (OCT-A)

Published on
December 4, 2023
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Optical coherence tomography angiography (OCT-A) is a non-invasive scan that creates a three-dimensional image of the network of blood vessels in your eye by tracking individual blood cells.

OCT-A gives insight into small changes to the blood vessel network before they develop, making it particularly useful for early diagnosis and monitoring of retinal eye diseases, including glaucoma, macular degeneration, choroidal neovascularization, diabetes, vein occlusions and optic neuropathies.1,2,3

The optometrists at Innovative Eye Care use the top of the range Heidelberg Spectralis OCT-A to obtain high-quality, precision images at high speeds.

How does OCT-A work?

Conventional OCT scans assess the eye’s structural integrity by analysing light that is reflected from the back of the eye (the retina). When multiple OCT scans are taken of the same location, changes in the reflection pattern over time can be used to produce another specialised scan – the OCT-A scan. Because the only thing that is changing and moving as the scan is being taken are the blood cells, the OCT-A scan can track and assess the flow of blood.

OCT-A of a healthy eye

Figure 1. OCT-A scan of a healthy eye, showing rich foveal vasculature.

OCT-A in Glaucoma

Glaucoma is a progressive eye disease that causes gradual optic nerve damage over time. In the early stages, people with glaucoma don’t notice any vision loss. Due to the insidious nature of glaucoma, it can be difficult to detect and diagnose in the very early stages with conventional imaging.

Recent evidence has shown there is a strong link between the eyes blood vessel network and glaucoma.2,3 The flow of blood and the amount of blood itself in surface-level vascular perfusion and blood flow density within superficial retinal vessels has been found to be significantly decreased in glaucomatous eyes, when compared to healthy eyes.4This difference is noted prior to any vision loss occurs and may be used to differentiate between healthy eyes and those with pre-perimetric glaucoma (i.e. Structural glaucomatous changes have occurred without causing a measurable visual defect).5

By analysing the blood vessels with the high-definition OCT-A scans in combination with conventional OCT, we can detect glaucoma and monitor the risk of glaucoma development much earlier and with greater accuracy.2, 3, 4, 5

Figure 2. an OCT-A scan of the superficial capillary network in a glaucoma patient, showing loss of perfusion that corresponds with overlying loss of nerve tissue.

OCT-A in Diabetes

Diabetic retinopathy is the most common ocular complication of diabetes, this is a disease of the microvasculature. CT-A is the first scan to be able to assess the microvasculature in such high detail. Eyes that are affected by diabetic retinopathy have a significantly reduced choroidal and retinal vascular density as well as an abnormally large foveal avascular zone.7

To date, the first sign that an eye is developing diabetic retinopathy is the presence of micro-aneurysms (“out-pouching” of blood vessels). Evidence has recently shown that linear vascular dilations and flow-void areas within the retina as seen on OCT-A, precede the appearance of micro-aneurysms and allow earlier diagnosis and detection of diabetic retinopathy.8

OCT-A in diagnosing Rare Macular Conditions

At first glance, when assessing conventional retinal photos and OCT scans, this eye appears to have vitreomacular traction. This is a benign and common pathology seen in many eyes that does not require any management and is generally not vision threatening. The retinal blood vessels also appear to be normal on conventional retinal photos.

OCT-A of this eye has shown abnormal enlargement of the deep capillary network which is indicative of a rare form of macular telangectasia.6 This is a vision threatening condition and would have been missed if only conventional imaging of the retina was done.

References

1) Hagag, A. et al. (2017). “Optical coherence tomography angiography: Technical principles and clinical applications in ophthalmology”. Taiwan J Ophthalmol. 7(3): 115-129.

2) Rao, HL. Et al. (2017). “Diagnostic ability of peripapillary vessel density measurements of optical coherence tomography angiography in primary open-angle and angle-closure glaucoma”. Br J Ophthalmol.101(8): 66-70.

3) Lommatzsch, C. et al. (2018). “OCT-A vessel density changes in the macular zone in glaucomatous eyes”. Graefe’s Archive for Experimental and Clinical Ophthalmology. 256(8): 99-508.

4) Alnawaiseh, M. et al. (2018). “Correlationof flow density, as measured using optical coherence tomography angiography, with structural and functional parameters in glaucoma patients”. Graefes ArchClin Exp Ophthalmol.

5) Cennamo, G. et al. (2017). “Optical coherence tomography angiography in pre-perimetric open-angle glaucoma”.Graefes Arch Clin Exp Ophthalmol.

6) Dogan, B. et al. (2019). “Retinal vasculardensity evaluated by optical coherence tomography angiography in macular telangiectasia type 2”. Int Ophthalmol.

7) Conti, FF. et al. (2018). “Choriocapillaris and retinal vascular plexus density of diabetic eyes using split-spectrum amplitude decorrelation spectral-domain optical coherence tomography angiography”. The British Journal of Ophthalmology.

8) Lupidi, M. et al. (2017). “Retinal microvasculature in non-proliferative diabetic retinopathy: automated quantitative optical coherence tomography angiography assessment”. OphthalmicResearch. 58(3): 131-141.

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