Imaging the Circulation of the Posterior Segment

Published by Auckland Eye on Tuesday, 04 Oct 2016

Imaging the dynamics of the retinal circulation was first devised by two medical students in 1959 who discovered by injecting fluorescein intra-venously they could with appropriate excitation and emission filters, could indeed visualize the retinal vascular tree. Other improvements have occurred since the original inception, digital images replacing film being a major step forward. More recently wide-angle imaging systems have been developed which have enabled imaging of the peripheral retina, important in inflammatory eye conditions and certain inherited disorders (OPTOS).
With the advent of indocyanine angiography,  imaging the choroidal circulation became possible, revealing important clues about the genesis and types of macular degeneration, central serous retinopathy and as a result enabled refinements and treatment options for a new variety of diseases.
When optical coherence tomography (OCT) was introduced a decade ago it looked as though it might replace fluorescien and ICG angiography; it is less invasive, provides breathtakingly accurate detail of the retina and choroid and a new way of looking at the same pathology. As an example cystoid macular oedema following cataract surgery is routinely diagnosed and monitored by OCT, fluorescein angiography only rarely used.
Now a new modality has arrived: OCT angiography a clever technology, which utilizes amplitude and phase OCT signals to image the retinal circulation. All this without the need for intra-venous injections or dyes, or a camera flash. The resolution of OCT angiography matches and in some instances exceed the  traditional methods although there are some limitations particularly with the inability to demonstrate vascular leakage, although this can be inferred from fluid filled spaces on conventional OCT. Another limitation is the size of the field, much less than a 30-degree field and certainly much smaller achieved with wide angle viewing systems, but for ease of use, rapid imaging is certainly a new tool in diagnosis.

OCT Angiography is available at Auckland Eye's Papatoetoe location (24 Hoteo Ave, Papatoetoe), where Assoc. Prof. Philip Polkinghorne and Dr Jo Sims see patients.

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