Focus On. . .
FOCUS ON. . .
A New Light on Multispectral Imaging
BY STUART MICHAELSON
The RHA 2020-U multispectral digital ophthalmoscope, from Annidis Health Systems, may be clearing a new path in visualizing and diagnosing retinal disease and glaucoma.
Stephen Sinclair, MD, who has used the RHA to manage AMD, DR, and glaucoma since its 2011 FDA approval, expects imaging to move to the forefront of retinal evaluation because it can reveal lesions that funduscopy can miss and help monitor physiological changes.
The Annidis RHA — for Retinal Health Assessment — uses multispectral imaging (MSI) to replace white light or simple photography that uses camera filters.
The role of RHA in managing AMD, Dr. Sinclair says, involves showing “how drusen change over time,” which can lead to improved patient education and early diagnosis, particularly with RP.
“We commonly pick up DR far too late because patients don’t visit the eye doctor for routine screening,” Dr. Sinclair says. “It’s only after vision loss is sufficient to affect lifestyle that they present.”
Dr. Sinclair cites “the wow factor” when patients see overlays of multiple images that show progression of their disease. MSI with overlay “is the way we must go, and we must use images to educate patients,” he says. Also, RHA is useful to monitor anti-VEGF therapy, Dr. Sinclair notes.
BROAD WAVELENGTH RANGE
“Current imaging systems, including fundus cameras and scanning lasers, are capable of imaging at several wavelengths (three to a maximum of four) utilizing white light with filters or multiple discrete lasers,” Nick Ribaric, president and founder of Ottawa-based Annidis, explains. RHA, meanwhile, utilizes up to 12 specific monochromatic LEDs to capture the data of the retina and choroid, he says.
RHA images the choroid with trans-scleral choroidal illumination (TCI), a non-invasive visualization of the choroid and retinal vasculature that uses oxygenated and deoxygenated blood and provides stereo imaging without moving the patient. RHA has fundus autofluorescence at 660 nm and retinal video at 100 frames per second.
“Based on differential absorption in different retinal layers with various pigments, we can observe new information not seen before,” Mr. Ribaric says. The RHA has a wavelength range of 510-950 nm compared with 500-620 nm for a fundus camera and 780 nm for OCT, according to Annidis.
That broad wavelength range creates a series of discrete en face spectral slices highlighting features within the entire span of the retina, from the internal limiting membrane through to the choroid, Mr. Ribaric says.
FUNCTION OF WAVELENGTHS
“Short wavelengths, such as yellow and amber, highlight epiretinal membranes and hemorrhages while longer wavelengths effectively show disruptions in the retinal pigment epithelium,” Mr. Ribaric adds. Melanin absorbs light of longer wavelengths (red and infrared) and “cannot be visualized using traditional fundus cameras.”
RHA is unique, according to Mr. Ribaric, because it can provide early RPE change detection not visible clinically or with some other imaging technologies; identifies RPE pigment changes, including melanin and lipofuscin; visualizes choroidal vasculature using TCI and differentiation of nevi from melanomas; and determines oxygenation in retinal and choroidal vasculature based on the hemoglobin.
Short wavelengths can reveal vitreomacular traction; medium wavelengths can visualize hemorrhages; and long wavelengths can image RPE disturbances.
Dr. Sinclair endorses RHA because third-party payers require photographic screening for diagnoses of AMD and because patients with DR require regular exams. RP
Retinal Physician, Volume: 11 , Issue: January 2014, page(s): 69