Richard F. Spaide, MD
Speaker topic: Imaging the Choroid with Optical Coherence Tomography
The choroid is a new frontier for ocular imaging. It has the highest blood flow of any tissue of the body and delivers prodigious amounts of oxygen to the outer retina, a structure with the highest metabolism. The choroid is also thought to act as a heat sink and participates in immune responses as well. The choroid is a difficult structure to image as ultrasonography has low axial and lateral resolution, fluorescein angiography is constrained by light absorption and scattering and indocyanine green angiography has poor resolving power and no depth information. Optical coherence tomography (OCT) has the potential for fast, high resolution, depth resolved images. However, OCT is limited by factors including scattering and absorption of light and roll off in sensitivity with depth. OCT angiography has these limitations, as well as motion and projection artifacts. Creative solutions have enabled some of these problems to be at least partially addressed. The ultimate destination of choroidal blood flow is the choriocapillaris, a dense network of capillaries that has proven to be particularly difficult to image. This presentation will trace the developments in imaging the choroid, especially the flow within the choriocapillaris using OCT. Human histologic images will be compared with the OCT angiographic images of the choriocapillaris and adjacent vessels. We will show that likely contributors to the image obtained are composed of projection artifacts from the choriocapillaris and a variable amount of projection and direct visualization of vessels immediately below the choriocapillaris. All of this is convolved, in turn, by the spot size of the illuminating beam.