Optical Coherence Tomography Angiography (OCTA) is an advanced, non-invasive imaging technique used in eye care. This technology creates detailed, cross-sectional images of the eye’s internal structures, specifically focusing on blood flow within the retina and choroid. It provides visualization of intricate vascular networks that are otherwise difficult to observe without invasive procedures. This diagnostic tool aids eye care professionals in understanding various eye conditions.
Understanding OCT Angiography
OCT Angiography builds upon the principles of Optical Coherence Tomography (OCT), which uses light waves to capture high-resolution, two-dimensional images of retinal structures. To visualize blood flow, OCT Angiography employs a technique called motion contrast. It takes multiple rapid scans of the same retinal area. By comparing these sequential scans, the system detects subtle differences caused by the movement of red blood cells within blood vessels, while static tissue remains unchanged.
This process generates detailed maps of blood vessel networks, including tiny capillaries at various depths within the retina and choroid. Light is emitted through either a spectral domain OCT (SD-OCT) system (near 800nm wavelength) or a swept-source OCT (SS-OCT) system (longer wavelength, close to 1050nm). Longer wavelengths offer deeper tissue penetration, though with slightly lower axial resolution. To enhance image quality and reduce noise from eye movements, OCT Angiography uses averaging techniques.
Key Advantages Over Traditional Imaging
OCT Angiography offers advantages over traditional imaging methods, particularly conventional fluorescein angiography (FA). A primary benefit is its non-invasive nature, as it does not require dye injection. Traditional FA involves injecting a fluorescent dye, which can lead to side effects such as nausea, skin discoloration, or, in rare cases, severe allergic reactions.
The absence of dye makes OCT Angiography a safer option for patients, especially those with kidney issues or dye allergies. OCT Angiography is faster than FA, with scans taking only a few seconds per eye. This speed allows for quicker patient throughput and a more comfortable diagnostic process. The ability to perform repeatable scans without dye injection risks facilitates more frequent monitoring of eye conditions.
Conditions Diagnosed and Monitored
OCT Angiography aids in diagnosing and monitoring various eye conditions by visualizing specific vascular changes. For age-related macular degeneration (AMD), it detects abnormal new blood vessel growth, known as choroidal neovascularization (CNV), which often causes vision loss in “wet” AMD. It helps identify the size and extent of these neovascular lesions, even those difficult to see with traditional methods.
Diabetic Retinopathy
In diabetic retinopathy, OCT Angiography reveals early signs of capillary dropout, areas of reduced blood flow, and changes in the foveal avascular zone (FAZ), the central area of the retina without blood vessels. It also detects intraretinal microvascular abnormalities (IRMAs) and neovascularization, providing detailed insights into disease progression.
Retinal Vein Occlusions
For retinal vein occlusions, OCT Angiography assesses the extent of non-perfusion (areas without blood flow) and shows abnormal vessel tortuosity or dilation.
Glaucoma
In glaucoma, it identifies reduced blood flow around the optic nerve head capillaries, correlating with potential nerve damage and aiding in earlier detection of structural changes.
What to Expect During the Procedure
Undergoing an OCT Angiography scan is a straightforward and generally comfortable experience. Patients sit in front of the machine, resting their chin on a support to keep their head still during imaging. In some cases, dilating eye drops may be administered to widen the pupils, making it easier for the machine to capture retinal images.
The procedure is quick and non-contact. The device emits a harmless laser light into the eye, capturing multiple images through rapid scanning, taking only a few seconds per eye. Patients are asked to look at a designated target or light to ensure proper eye alignment. Afterward, there is typically no recovery time, and patients can resume normal activities immediately. Results are often available soon after the scan.