The issue in this project is "will optical coherence tomography angiography (OCT-A) become an alternative to fluorescein angiography (FA)?" Invasive ophthalmic examinations are accompanied by pain, contact, and photophobia. They may require contrast agents, be time-consuming, and involve biopsy. The development of improved or alternative approaches can make examinations minimally invasive. Moreover, improved test accuracy facilitates early detection of disease, which in turn reduces the need for invasive treatment. In particular, FA is a relatively invasive test that can lead to serious complications, although at a low frequency. In addition, the testing duration is long, and it is accompanied by pain associated with photophobia due to mydriasis and the establishment of a peripheral intravenous line. However, it is an essential test for the diagnosis and treatment of several retinal diseases. The developmental improvement and research on alternative tests are expected to contribute considerably to the development of ophthalmology.
OCT-A is a device that allows high-contrast retinal angiography without the need for contrast media, and it has been attracting attention as a minimally invasive alternative to FA. However, it is impossible to simply replace fluorescein fundus angiography with OCT-A even to this day, although commercial OCT-A devices were introduced 5 years ago. Compared with FA, whose scientific basis for the interpretation and determination of treatment and the findings on treatment efficacy have been well established for over half a century, those for OCT-A have not been well-established. Moreover, OCT-A is underdeveloped as a clinical device and has fatal drawbacks: the image quality is unstable, and it has quantitative instability, although quantitation is easy. We planned to improve the performance of OCT-A as a clinical device by elucidating about the items that need to be developed to facilitate its implementation as an alternative to FA.
I. Basic study on vessel depictability of OCT-A
The method for depicting blood vessels is completely different from that used in FA. Although the theoretical part is understood, there have been no reports on direct observations of how blood flow signal depicted by image processing corresponds to the actual microcirculation dynamics; therefore, this remains unknown. With respect to future growth, it is important to understand why it can or cannot depict images during direct visualization of microcirculation. This area of depictability needs to be demystified because it cannot be avoided and has indeed been a black box for an extensive period of time. The movement of blood cells was visualized using an adaptive optical scanning laser ophthalmoscope, and the effects of blood cell density and flowing blood cell types on OCT-A depictability were verified at a cellular level.
II. Study on high-quality imaging
One of the major problems with OCT-A, which is reconstructed from a volume scan, is the stabilization of image quality. We examined the effects of high-quality imaging on quantitative evaluation using signal averaging and artificial intelligence (AI).
III. Study on wide-angle imaging
The narrowness of the angle of view of OCT-A has been a problem. In recent years, the angle of view has been increasing. However, there has been a trade-off between the angle of view and image quality, and it has been highlighted that a wide angle of view leads to a decrease in image quality. We investigated the extent to which the ocular fundus can be captured using OCT-A and how clinically useful it is.
IV. A study on the advantages of OCT-A over FA
Although it is expected to be an alternative to FA, the major advantage of OCT-A is that it can be used to obtain information that is difficult to obtain with FA, which is a major reason why OCT-A has been drawing attention. We investigated the visualization and quantitative evaluation of the anterior segment and choriocapillaris by OCT-A.
Nippon Ganka Gakkai Zasshi (J Jpn Ophthalmol Soc) 126: 298-325,2022.