ARVO 2023: Using visible light, OCT to image the retina

Vivek Srinivasan, PhD, sat down with David Hutton, Managing Editor, Ophthalmology Times®, to discuss his presentation about using visible light, OCT to image the retina at this year's ARVO meeting.

Video transcript

Editor’s note: This transcript has been edited for clarity.

David Hutton:

I'm David Hutton of Ophthalmology Times. The Association for Research in Vision and Ophthalmology recently held its annual meeting in New Orleans. I'm joined today by Dr. Vivek Srinivasan, who made a presentation at this year's event. Thanks so much for joining us today. Tell us a little bit about that presentation.

Vivek Srinivasan, PhD:

Thank you. It's great to be here. So our presentation was about using visible light, OCT or optical coherence tomography, to image the retina. Now, visible light OCT, is similar to the standard commercial OCT that's used everywhere, in ophthalmology clinics, except it uses a visible wavelength of light instead of near infrared light. And so, what this allows us to do is get very, very high or very fine axial depth resolution images of the retina that allow us to see layers within layers of the retina and new bands that are not seen on near infrared, OCT.

So in this particular study, which was also led by a postdoctoral fellow Pooja, Chauhan as well as a former PhD student, Aaron M. Kho, we used visible IOCT with very high resolution to look at a particular band in the outer retina. This is band 2, which is sometimes known as the ellipsoid zone, or mitochondrial zone. and It's alternatively sometimes known as the intersegment outer segment junction. It's a very clinically important band, so missing this band indicates a poor prognosis for patients.

However, there's a lot of controversy about what it actually represents. So here we use the high resolution imaging with a visible IOCT in mice to do a more careful investigation of band 2. We perform visible IOCT, and follow this up with measurements, ex vivo of electron microscopy. So, we perform in vivo imaging in the living eye. and then we compare those results with microscopy of mitochondria as well as the intersegment outer segment junction.

What we found was that actually, the visible light OCT reflectivity agreed much better with the ISOS junction than it did with the mitochondrial profile. And in fact, when we zoomed in with very high resolution on the micron scale, and we looked at that region between the myeloid and ellipsoid, we actually found that the myeloid had a higher reflectivity than than the ellipsoid, where the mitochondria are. So this, this result actually challenges the long standing belief that mitochondria are always highly scattering. and it suggests that the current interpretation of band 2 as being due mainly to mitochondria scattering within the ellipsoid needs to be reevaluated. and I think this is an important study, because the stakes are pretty high. This is something that's used in patients. and it's important to get the interpretation correct so that we can interpret the data correctly.

More broadly, our research group is following up on these studies, with measurements in aging, as well as in patients with age-related macular degeneration. and I'll say visible light OCT has been a very exciting technology for us to work with, because we've discovered, in addition to these findings in a number of other studies, a number of new bands and new layers or strata within the retina that could be important in both understanding disease, but also in understanding the function of normal vision.

David Hutton:

What's the next step for your research?

Vivek Srinivasan, PhD:

Yeah, so as I mentioned, we are doing studies in aging, to look at how some of these bands change with age and correlate those with different findings histologically. And we're also starting studies in humans actually in age-related macular degeneration, and we believe that some of these new bands seen by visible light OCT can provide prognostic biomarkers for MD progression. and this is particularly important. As we've heard at this conference, there are a number of promising treatments for dry age-related macular degeneration to prolong the end stage. And so if we can develop new biomarkers that tell us early on when a patient is going to progress, we can design more effective clinical trials for some of these new treatments.