OCT-Angiography: everything you need to know!

Several diseases of the eye result in the development of intraretinal edema, circulatory failure or abnormal vessels within the eyes. Even a few years ago, it was only a lofty dream to be able to clearly visualize the choroidal circulations and retinal circulations, without the injection of contrast dyes. With the advent of medical technology came the Optical Coherence Tomography Angiography (OCT-Angiography) method that made the dream reality. Today, ophthalmologists can perform this non-invasive visualization process as many times as necessary on people with benign or severe eye conditions. 

What is OCT-Angiography?

The OCT Angiography method is a derivative of the OCT process. It reconstructs the multiple scans in a 2-Dimensional horizontal plane into a single 2-Dimensional image. According to the principles of the process, the outcome highlights the changes in images that occur only between two-time points (t1 and t2). Therefore, in the final result, you can expect to see only the changes in the image after the removal of the fixed components. The walls of the blood vessels will not be visible, but the flow that circulates within will be.

The important advantages of the technique –

  • Since no dyes are involved, the process is cleaner and safer than the older angiographic methods.
  • The ophthalmologist can recommend this test multiple times for the patient, since the method is completely non-invasive and painless.
  • One of the primary advantages of the process is that the artifacts of the traditional angiographic techniques are not present. You will not be able to see the dye staining, leakage or pooling that are almost ubiquitous to conventional angiograms.
  • This technique can delineate the individual vessels adjacent to the foveal avascular zone (FAZ). It is a sharp improvement over techniques including dye contrast angiography.

The apparent disadvantages of the technique –

  • One of the most significant drawbacks of this advanced technique is the inability to discern the nature of the flow. The software might not be able to highlight if the flow inside the vessel is too slow or too rapid.
  • Other artifacts of the process might include the ones related to eye movements. Thankfully, to our advantage, as the technology advances, these artifacts are becoming less prevalent in the results.
  • The currently available protocols for automated scans are 2 mm by 2 mm, 3 mm by 3 mm, 6 mm by 6 mm, and 8 mm by 8 mm. the number of cross-sectional OCT scans are limited. Hence the larger field of view often lacks density and high resolution.

While talking about its advantages and disadvantages, it is important to remember that OCT-Angiography is still a new technique. As the experts are fine-tuning the process, the limitations and artifacts are reducing. It might soon be possible to use this non-invasive imaging technique to view the retinal and eye microstructures without any false positives at all. Right now, experts have to be a little vigilant about the false positives that may arise from the presence of high reflective fundus components and fluid disorders.

How does OCT-Angiography contribute to diagnostics?

The generated maps are the 2D representations of the vascular structures of the different parts of the eyes that help in studying the morphology of various eye diseases like Retinal vein occlusion (RVO), diabetic retinopathy (DR) and macular telangiectasia type 2 (MacTel).

OCT-Angiography helps in the study of the retinal vasculature

The retinal vasculature is in the form of morphologically distinct layers. The ganglion cell layer contains the superficial retinal capillary plexus, the outer boundary of the inner nuclear layer contains the deep retinal capillary plexus and the inner margin of the inner nuclear layer hosts the smaller intermediate retinal capillary plexus. Several perpendicular blood vessels connect the distinct vascular layers of the retina. OCT-Angiography has become of the most sought-after tools for ophthalmologists thanks to its ability to analyze each aforementioned plexus individually.

It has enabled the study of chorioretinal diseases

Currently, several doctors are recommending OCT-Angiography for the diagnosis of chorioretinal diseases and their progression. According to several research papers, application of this technique can help determine the effect of anti-VEGF therapy on the choroidal neovascularization (CNV), apart from pinpointing the location and morphology of the CNV. According to further studies, there is over 95% agreement between the results of an OCT-Angiography and traditional imaging protocols for a “treatment required” opinion, and there was a 91% agreement in the case of a “treatment not necessary” decision.

It helps in studying the progression of age-related macular degeneration non-invasively

The diagnosis of age-related macular degeneration has become accurate with the help of OCT-Angiography. The non-invasive technique enables the specialist to check the extent of damage by viewing the decrease in the choriocapillary flow in and around the areas of the atrophy. The OCTA technique has been instrumental in the qualitative and quantitative analysis of the CNV membranes in case of both dry age-related macular degeneration and wet-age related macular degeneration. 

It can help is the diagnosis and study of optical nerve disorders

Apart from retinopathies, OCT-Angiography is gaining steady popularity in the detection of optic nerve disorders like glaucoma. In the cases of glaucoma, experts had used this technique to study the optic disc perfusion, when pre-perimetric patients showed the presence of distinctly attenuated macular and peripapillary vessel densities. As a result, there is increasing enthusiasm about the ability of OCT-Angiography to detect any glaucomatous damage. It provides a quantitative as well as a qualitative analysis of the damage due to the progression of the genetic disorder. It may prove to be a useful instrument in the comprehensive analysis of the metabolic data from the retinal layers. It can help in the continuous monitoring of the otherwise complex disease and study its progression in patients. 

OCT-Angiography is the future of the diagnosis of eye diseases

Over the last one-and-a-half decades, OCT technology has made astounding progress. Currently, OCT-Angiography provides clinically essential data necessary for the determination of eye diseases that can be sporadic or genetic. Since it uses the principles of the detection of diffractive particle movement, it can quickly generate the images of conditions related to retinal microvascularization.