OCT-A stands for optical coherence tomography-angiography, which is a promising technology still under investigation. Currently, fluorescein angiography (FA) is the standard of care for evaluating numerous retinal diseases, but it requires the intravenous injection of a dye with subsequent photography to visualize the retinal vasculature. OCT-A, on the other hand, allows for the noninvasive imaging of the retinal vasculature. 

Instead of using the optical scattering properties of tissue to provide 3-D images, which normal OCT does, OCT-A looks at the variation in the intensity and phase of the light caused by the flow of red blood cells. OCT-A differs from FA in that the OCT-A signal reflects off of red blood cells, rather than being emitted by fluorescein dye. Based on the properties of the light reflected from these blood cells, we can tell that blood cells are in motion and identify retinal vessels. 

What are the primary advantages of OCT-A?

The primary clinical benefit of OCT-A is that the clinician can image both eyes as many times as desired without the need for intravenous dye injection. If the patient blinks, for example, retaking the picture requires only a few seconds. OCT-A can eliminate the complicated step (as well as the potential side effects) of injecting the patient with dye, and also the time-sensitive process of capturing a series of images during the circulation of the dye. Being able to conveniently image both eyes is a huge benefit compared to fluorescein, where the doctor has to choose the “most important” eye for imaging. 

Also, the small-vessel resolution of OCT-A is in many cases superior to FA. In fact, it is very close to the resolution of histology in some ways. 

how are you testing oct-a clinically?

Currently, my team and I are testing OCT-A on the ZEISS CIRRUS device in a number of investigator-initiated, IRB-approved research studies. We are applying this imaging technology to eyes that have diseases affecting the retinal vasculature, such as diabetic retinopathy, retinal vein occlusions, retinal arteriolar occlusions, etc. We are also starting to examine diseases that affect the choroidal vessels. 

In many cases, I foresee OCT-A to be a viable alternative to fluorescein angiography, because it is faster, non-invasive, and has excellent spatial resolution

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