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OCT angiography: the next big thing

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Dr Alan Burrow
DipOptom FBOA(HD) DCLP DOrth FBCO MSc(Med) GCOT MOptom

Product
Optovue Avanti RTvue XR OCT with Angiovue 3D OCT Angiography

Supplier
BOC Instruments

 

After I introduced the RTvue OCT into my practice in 2009, it became the primary instrument to diagnose and monitor an increasing number of ocular conditions.

Last year, I upgraded to the Optovue XR-Avanti OCT because of its additional features and improved imaging. I also decided to include the optional Angiovue 3D OCT Angiography module. This was due to the magnificent insight it provides into the microvasculature of the retina and choroid, which are subject to pathological changes in a wide range of retinal conditions such as macular degeneration, diabetic retinopathy and glaucoma.

Unlike most methods of imaging, which record structures such as retinal vessels, Optovue angiography utilises a technique of decorrelation by recording differences in repeated scans. The constant movement of the blood through the vessels is detected while fixation fluctuations are cancelled by a tracking mechanism. As a result, only vessels that have blood flow are visible. Vessels with a reduced lumen have a correspondingly reduced blood column with a narrower angiographic image.

 

EQ120 Figure 1 - online.jpg

Figure 1. Optic nerve head capillaries, angio OCT image

 

OCT-A vs FA and ICG

Traditionally, ophthalmologists have investigated circulatory disorders in the retina with two-dimensional fluorescein and/or indocyanine green angiography, but these techniques are invasive and have not been available to our profession.

OCT angiography enables optometrists to extend their diagnostic capability, particularly in marginal situations in which the cost and risk of the more invasive techniques are not justified.

The disadvantages of fluorescein and indocyanine green angiography are well known. They are time-consuming and expensive, and they cannot be used routinely because of their potential side-effects including nausea, vomiting and the rare possibility of anaphylaxis. OCT angiography is free of these difficulties and has the further benefit of offering a 3-D evaluation of vessels at different levels within the retina and choroid without the disadvantage of deeper vessels being obscured by dye leakage.

Angiovue in practice

The normal structural OCT of the retina and optic nerve remain essential but in all cases, it can now be complemented by angiography, which can be performed on both the retina and the optic disc. Image capture is quick and can be performed repeatedly as required, either separately or as part of an overall protocol.

All the images in this article were taken in my practice. They are intended to demonstrate the additional information provided by angio OCT.

A highly comprehensive reporting system can be selected according to the suspicion of pathology and clinician’s preferences. These commonly include en face angiography of the superficial, deep and outer retina of the macula, as well as the choroid capillary layer (Figure 3). In addition, a cross-sectional view of the retina indicates the level being displayed. Similar reports are available for the optic disc, which includes an angiographic view of the nerve head (Figure 1), vitreous, radial peripapillary capillaries and choroid.

AngioAnalytics is another innovative method of analysis that enables measurement of both flow and non-flow areas as well as vessel density. This can be useful in assessing neovascularisation and areas of non-perfusion which can be associated with capillary drop-out.

Whither angiography?

OCT angiography is a revolutionary development that will have a major impact on future assessment of retinal pathology. I recently referred a patient with an atypical form of macular degeneration that had developed rapidly over a three-month period. It was limited to one eye, with no signs of pathology in the other. The ophthalmologist to whom he was referred was astounded by the additional insight afforded by the OCT Angiography.

He subsequently performed a fluorescein angiogram but felt that the information gained was inferior to that of the angio OCT, raising the possibility that angio OCT may replace fluorescein angiography in the future.

Although the instrument is intuitive, as with all new developments there is a learning curve in becoming familiar with both the capabilities of the instrument and the techniques needed to procure high-quality images. A detailed study of the angiographic appearance of various forms of pathology is essential for accurate diagnosis and ongoing monitoring.

As use of this technique becomes more widespread, expansion of the knowledge base will inevitably be associated with an increased diagnostic ability.

 

EQ120 Figure 2 Fundus - online.jpg

Figure 2. Normal fundus. The box indicates the scanned area of the macula shown in Figure 3.

 

EQ120 Figure 3_Layer scan - online.jpg

Figure 3. Cross-sectional view of the retina. Colour enhancement is for illustrative purposes only.

 

EQ120 Figure 3A-3D_Layer scan - online.jpg

Figure 3A: Normal superficial vascular network. Figure 3B: Normal deep vascular network. Figure 3C: Normal outer retina avascular zone. Figure 3D: Normal choroid capillary layer.

 

EQ120 Optovue Avanti RTvue XR OCT - online



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