This article is more than 5 years old. Information may no longer be current.
Is OCT angiography going to change our lives?
Click Here to Manage Email Alerts
OCT jumped into our lives in 1991 when Huang and colleagues published about a “noninvasive cross-sectional imaging technology in biological systems.” Since then, major advancements have been made. Spectral-domain and swept-source OCT platforms brought faster scans and higher resolution. Also, OCT technology has been proposed in conjunction with adaptive optics, which may allow further resolution, up to a single photoreceptor cell. Polarized light combined with high-resolution OCT scanning may improve characterization of the retinal pigment epithelium. No doubt, therefore, that with the introduction of OCT, assessment of fundus structure has dramatically increased.
Amelioration of knowledge on retinal function is also possible thanks to OCT. Functional ultrahigh-resolution OCT may allow the study of retinal response to light stimulation. Quantitative imaging of fundus blood flow and pulsatility of retinal and choroidal vasculature has been proposed with color Doppler OCT.
More recently, a new application, OCT angiography (OCTA), has been introduced, based on motion contrast imaging to high-resolution volumetric blood flow information generating angiographic images in a few seconds. Similarly to the early times of time-domain OCT, many of us have passionately started performing OCTA in normal and pathologic patients. Although the enthusiasm for this noninvasive newer technology is more than justified, we have to recognize that there are still many limitations. Obviously, the current and potential advantages of such an examination technique deserve extensive dedication.
OCTA is capable of displaying volumetric data on vascular flow without the injection of any dye, and this is definitely a major advancement over traditional angiography. Probably the most appropriate name for OCTA would be OCT “angioflowgraphy.” In fact, different from standard fluorescein or indocyanine green angiography, OCTA detects the presence of blood flow, although it cannot give any information on leakage or pooling. However, with OCTA, flow at different fundus levels such as the superficial and deep inner retina and choriocapillaris can be differentiated and imaged. In diabetic retinopathy, OCTA allows us to clearly visualize the foveal avascular zone (FAZ) both at the superficial and deep layer and to understand that most microaneurysms are located in the deep plexus and an enlargement of the FAZ is more pronounced in the deep layer as well. However, compared with fluorescein angiography, the number of microaneurysms detected by OCTA is lower due to slow blood flow, which may be below the detectable threshold.
At the European Institute of Ocular Microsurgery (IEMO) in Udine, Italy, we are testing OCTA with the swept-source DRI OCT Triton by Topcon using a ratio method called OCTARA (OCT angiography ratio analysis), in which the full spectrum is kept intact, therefore preserving the axial resolution. This equipment uses a long wavelength scanning light at 1,050 nm, which allows increased light penetration into pigmented tissues and improved choroidal blood flow identification compared with spectral-domain sources. We compared OCTA to standard angiography findings. In wet age-related macular degeneration, type 2 choroidal neovascularization is usually visible in almost all cases, whereas type 1 CNV can be detected by OCTA scans in about 65% of cases.
Artifacts may include motion artifacts, large retinal vessels projecting ghost images on the outer retina, horizontal black lines due to blinking, white noise at the edges of a pigment epithelium detachment, and white dots in cases of retinal hard exudates.
Experience plays a pivotal role in identifying pathological findings, especially at the choroidal level. Also, software evolution and new algorithms may allow improved definition and fewer motion artifacts. Recently, the possibility of assigning different colors to the different layers scanned has improved the possibility of analyzing the vessels of the various layers.
In summary, OCT angioflowgraphy is here to stay and has already changed our lives. Many physicians are currently performing OCTA on a routine basis on all patients who need an OCT scan. Continuous technological progress will contribute to keeping our lives very busy with OCT angioflowgraphy.
- For more information:
- Paolo Lanzetta, MD, OSN Europe Edition Chairperson, can be reached at Istituto Europeo di Microchirurgia Oculare, Via M.A. Fiducio, 8; 33100 Udine, Italy; email: paolo.lanzetta@iemo.eu.
Disclosure: Lanzetta reports no relevant financial disclosures.