Spectral Domain-Optical Coherence Tomography Angiography of Retinal Diseases

OCT is an optical ranging and imaging technique first described in 1991 that has since been used successfully to provide high-resolution, micrometer-scale depth imaging in clinical ophthalmology (and other fields). It can be thought of as the optical analogue of ultrasound imaging. For the ocular posterior segment, OCT provides rapid acquisition of high-resolution, cross-sectional images of the retina that approximate tissue histology. In vivo imaging of the retina with OCT has thus dramatically improved clinicians' diagnostic capabilities, allowing earlier and more accurate diagnosis of disease and more precise assessment of response to therapies over time.

While OCT provides important information on retinal anatomy, it is currently limited in its ability to provide information on retinal vasculature and blood flow. Angiography is the current gold-standard imaging modality for retinal vascular imaging. Angiography involves intravenous injection of a fluorescent dye (typically either fluorescein or indocyanine green for the retinal or choroidal vessels, respectively) that circulates through the body. A light source emitting light at the specific excitation wavelength of the dye is placed in front of the patient's eye, and a camera equipped with a filter corresponding to the emission wavelength of the dye is then used to image vessel morphology and retinal perfusion, either through still images or through a short movie. Angiography provides physiologic information about the retina that complements the anatomical information provided by OCT. While generally well tolerated by most patients, angiography does have drawbacks: it often requires the use of a separate imaging system, it requires several minutes for image acquisition, and it involves intravenous injection of a dye. Patients occasionally experience side effects of intravenous dye administration, including nausea, discomfort, and rarely, anaphylaxis.

Several retinal imaging companies are developing the next generation of OCT technology: OCT angiography (OCT-A). OCT-A allows noninvasive, high-resolution imaging of the microvasculature of the retina and choroid (the vascular plexus subjacent to the retina), without the need for intravenous dye administration. OCT-A platforms currently under development include both spectral domain (SD) and swept-source (SS) based technologies. Whereas SS-based OCT-A utilizes a longer wavelength (~1060 nm) light source, SD-based units use the same light source used in commercially available and FDA-cleared OCT units on a modified platform. Optovue, Inc. (Fremont, CA) has developed one such unit, a customized, high-resolution SD-OCT system that implements a novel algorithm, the amplitude-based method of split-spectrum amplitude-decorrelation angiography (SSADA) for OCT-A. This SSADA algorithm allows for detection of motion in the blood vessel lumen by measuring the variation in reflected OCT signal amplitude between consecutive cross-sectional scans. Optovue has integrated the novel SSADA algorithm into their commercially approved RTVue SD-OCT unit for their OCT-A unit, the AngioVue. The AngioVue can generate high-quality angiograms of both the retina and choroid. Additionally, this refined method has produced images of the smallest retinal vessels (capillaries) in normal healthy control participants. In this proposed prospective interactive clinical study, we will use the AngioVue unit to image patients and characterize vascular abnormalities that are present in the setting of retinal diseases.