Introduction:
OCT-A technology eliminates the requirement for intravascular dyes by precisely depicting vessels through various segmented eye parts using the laser light reflection of moving red blood cells. An OCT scan of an individual's retina comprises several separate A-scans combined to create a B-scan that offers cross-sectional structural data. OCT-A technology allows one to identify zones with high flow rates (i.e., with noticeable variations between scans) and zones with slower or no flow that will be similar among images.
The same tissue area is repeatedly photographed, and differences are examined between scans (over time). Understanding the distinctions between Doppler OCT and OCT-A is crucial. Even though they both employ phase information, OCT-A uses scatter from a static backdrop tissue to make angiograms. In contrast, Doppler OCT uses phase shifts to quantify blood flow in bigger arteries and estimate total retinal blood flow.
What Is Optical Coherence Tomography Angiography?
Using low-coherence interferometry, optical coherence tomography (OCT) is a noninvasive imaging method that generates depth-resolved images. Interferometrical measurements are made by interference with the backscatter or reflection from ocular structures using the known reference route of moving light after a light beam has scanned a specific portion of the eye, such as the retina or anterior eye.
When utilizing OCT, this adaptation of traditional Michelson interferometry enables the creation of structural pictures of anatomy. Since its debut in 1991, OCT has been extensively used in ophthalmology and has undergone continuous improvement. Phase variance or amplitude decorrelation are the two motion-detecting techniques used by OCT-A. The former identifies amplitude variations between two distinct OCT B-scans. The qualities of the emitted light waves and the phase variation that occurs when they collide with moving objects are related to phase variance.
What Are the Advantages of Optical Coherence Tomography Angiography?
The two biggest benefits are that the technique is non-invasive and takes less time to acquire data. An injectable dye is needed for fluorescein and indocyanine-green angiography; however, this dye takes time to reach retinal arteries and may cause systemic side effects, including anaphylaxis. An advantage of this OCT-based method is that in addition to the qualitative study carried out using traditional angiography, it offers a quantitative analysis of the retinal vessels. Furthermore, in contrast to traditional "2-D" angiograms, OCT-A technology shows peripapillary capillaries, which supply the retinal nerve fiber layer and offer "3-D" imaging information of the macula.
What Are the Uses of Optical Coherence Tomography Angiography?
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OCT-A may be useful in the diagnosis and treatment of CNVM (choroidal neovascular membrane), particularly in patients who raise suspicions regarding flat and uneven PEDs (pigmented epithelial attachment). Even if some publications state that the blood supply to the choriocapilaris is reduced, one needs to consider the signal strength in the facial pictures before interpreting this as hypoperfusion.
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Vascular Occlusions: Assessment of the superficial and deep plexus integrity and nonperfused regions. Improved visual results have been linked to the preservation of the deep vasculature.
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Identification of the dilated, asymmetrical telangiectatic vessels and, on occasion, the choroidal connection indicates macular telangiectasia.
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Diabetic Retinopathy: Excellent agreement with findings is demonstrated in identifying neovascular complexes and quantifying the foveal avascular zone and nonperfused regions.
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A general reduction in choriocapillaris flow has been described in dry age-related macular degeneration; this decline usually extends beyond the boundaries of areas of atrophy. SS-OCT (swept-source) using devices are linked to improved characterization of choroidal vascular alterations.
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Wet Age-Related Macular Degeneration: The ability to identify and monitor structural changes following intravitreal injections and qualitative and quantitative characterization of the choroidal neovascular membrane (CNVM). The possibility of finding these neovascular complexes in non-exudative cases, which would be challenging to find using SD-OCT has also been brought up. This could lead to a more thorough and efficient follow-up.
What Are the Clinical Findings of Optical Coherence Tomography Angiography?
As more people use the technology, OCT-A's clinical value continues to develop. OCT-A has demonstrated its usefulness in glaucoma, uveitis, and other retinal diseases. There are numerous impacts on the retinal vasculature linked to diabetic retinopathy. Using OCT-A to quantify nonperfused parts of the eye, such as the foveal avascular zone, and identify retinal alterations, such as microaneurysms or neovascular complexes, can help manage diabetic retinopathy.
The technique used to obtain OCT-A pictures permits the simultaneous viewing of cross-sectional and en-face-related B-scans, which facilitates the assessment of anatomical features with microvascular features seen on OCTA. OCT-A can also help assess choriocapillaris flow alterations, choroidal neovascular membrane characterization, and retinal change detection in age-related macular degeneration. OCT-A has also been demonstrated to have potential benefits in the care of other retinal illnesses, including choroidal neovascular membranes, macular telangiectasia, central serous chorioretinopathy, and vascular occlusion.
What Are the Limitations of Optical Coherence Tomography Angiography?
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There are certain limitations with OCT-A. OCT-A is extremely motion-sensitive, and while eye-tracking techniques are frequently used in devices, patient cooperation is necessary.
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Misalignment of the retinal vasculature or white or black lines are examples of motion artifacts. Imaging defective retinas can also result in segmentation mistakes, which are frequently corrected manually.
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Furthermore, the erroneous appearance of superficial vasculature in segmented views of deeper layers can result in a projection artifact.
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Finally, the automated visualization range that OCT-A currently offers is just 2 mm (millimeters) to 12 mm, which may further exacerbate the restriction of being unable to visualize the peripheral retina.
What Are the Complications of Optical Coherence Tomography Angiography?
OCT-A is a non-invasive imaging technique with few serious side effects.
Conclusion:
High-resolution cross-sectional retinal pictures can be obtained noninvasively with optical coherence tomography, or OCT. For early identification and diagnosis of retinal illnesses, the layers inside the retina can be distinguished, and retinal thickness can be assessed. Since then, OCT has established itself as the norm in the field of ophthalmology.
