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Multi-spectral imaging enhances visualization of deep retinal structures
Discrete monochromatic light sources may allow clinicians to examine individual retinal layers and identify early signs of pathology, experts say.
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A novel imaging technology enables detailed visualization of retinal structures that may contribute to early diagnosis of degenerative retinal disease.
Richard L. Lindstrom
The RHA (Annidis Health Systems Corp.) features multi-spectral imaging (MSI), which enables visualization of the individual retinal layers, Alan Boate, PhD, said. Boate is a member of an Annidis group that developed MSI for retinal imaging.
“What this allows us to do is explore areas of the retina that are not very visible in conventional fundus imaging but, most specifically, the retinal pigment epithelium,” Boate said.
According to Richard L. Lindstrom, MD, OSN Chief Medical Editor, MSI is a noninvasive alternative to fluorescein angiography and a valuable adjunct to optical coherence tomography.
Multi-spectral imaging can specifically explore the retinal pigment epithelium, according to Alan Boate, PhD.
“I don’t see it as a replacement for OCT. I see it more as a replacement for fluorescein angiography, which many of us don’t do because of the risks,” Lindstrom said. “If we can obtain the same information without having to start an IV and inject fluorescein into the eye, basically an injection-free angiography, that would be great. … It’s still in its infancy, but it’s basically going to be a new modality that will provide additional information.”
Pravin U. Dugel, MD, an OSN Retina Board Member, said MSI has the potential to complement OCT.
“It would absolutely be an adjunct to OCT,” Dugel said. “OCT will continue to be extraordinarily important for us. Whereas OCT will give you a slice of a very thin area of a very important part of the eye, which is the fovea, what this will do is give an overall picture, an en face image of whatever layer it is that you want to see. … We’re just beginning to learn what it can do.”
Monochromatic light sources
MSI uses 12 monochromatic light sources, or LEDs, at long wavelengths ranging from 550 nm to 950 nm, Boate said.
“One important advantage here is that we’re only putting light into the eye that we actually want to get back,” he said. “We’re not using a big, broad xenon flash and just collecting the wavelengths we want. We’re using LEDs that generate discrete wavelengths. We basically image those in pairs so a full series is six flashes, and that generates 12 individual images.”
MSI creates spectral slices of the retina that show deep retinal structures, Boate said.
“The information that we get from shorter wavelengths tends to be mostly the inner layer of the retina,” Boate said. “When we move to longer wavelengths, specifically about 670 nm or so, we’re really visualizing the deeper layers of the retina, the retinal pigment epithelium (RPE) and the choroid. It doesn’t slice like an OCT, but it does give you information from the different layers of the eye at different wavelengths.”
Specifically, the discrete light sources help detect melanin, a key pigment in the RPE, Boate said.
“Melanin in the eye is present in RPE cells and also in the choroid,” he said. “But this technique actually allows us to visualize the RPE directly. There are some other techniques, like some special long-wavelength autofluorescence techniques, that also show melanin, but we have the best way of showing melanin directly. The RPE is a critical layer in the eye, for the health of the eye.”
Biochemical and vascular signatures
Dugel noted that MSI can be used to gauge the effect of certain drugs on individual retinal structures.
“For instance, if you have a certain drug that you take and that drug is supposed to reduce or increase a certain type of material in the retina, you will be able to image this and see if it’s working or not,” Dugel said.
MSI may help clinicians gauge the effect of nutraceuticals such as beta carotene, copper, zinc lutein and zeaxanthin in the AREDS study and other analyses of AMD, Dugel said.
“If a nutritional agent is supposed to decrease something or increase something, you could actually image the retina before or after being on this medicine for a while and ask, ‘Is this working? Is this actually doing what it’s supposed to do,’ ” Dugel said.
MSI also has the ability to map retinal vasculature by detecting oxygenation of the blood, Dugel said.
Pravin U. Dugel
“What it does is really a virtual fluorescein angiogram,” he said. “Because blood that is oxygenated has a different adsorption pattern than blood that is not oxygenated, it can form an oxy/deoxy map. You can see what’s oxygenated and what’s not. You can actually do a virtual angiography that’s completely noninvasive.”
Managing AMD, vitreomacular traction
MSI will likely play a major role in managing dry macular degeneration, Dugel said.
“That’s the next big frontier,” he said. “This has the ability to detect changes at the layers of the RPE before anything at all that we know of now. … We can’t see it with photographs. We can’t even see it with autofluorescence. But we can see it with this at selected layers. So, we have the ability to find patients who have the earliest changes. That’s very significant.”
In addition, MSI will enable imaging of the vitreoretinal interface and help clinicians assess the effects of drugs such as Jetrea (ocriplasmin, ThromboGenics) on vitreomacular traction, Dugel said.
“We don’t really know which of the vitreomacular tractions will spontaneously release, and we don’t know which ones will continue to not release,” he said. “We’ll be able to image very early changes in vitreomacular interface disorders with this particular instrument. That’s just the tip of the iceberg.”
MSI will likely provide a ready supply of clinical images that can be stored electronically, Lindstrom said.
“As we move to electronic medical records, more of us are going to rely more and more on imaging,” he said. “We’re not drawing pictures as much as we used to. So, it does provide information that we don’t get with OCT. The goal is to enhance our diagnostic capabilities in a minimally invasive fashion.” – by Matt Hasson