Multispectral imaging (MSI) is an emerging diagnostic technology that permits the clinician to dissect and visualize the retina in spectral slices, from the inner limiting membrane all the way to the choroid.
Most importantly, however, MSI may help clinicians detect and evaluate several sight-threatening retinal and choroidal diseases, including diabetic macular edema, retinal pigment epithelium atrophy, vitreomacular traction syndrome and wet age-related macular degeneration.
Here, we’ll examine how MSI technology can help eye care providers effectively diagnose and manage retinal pathology.
Multispectral Overview
The concept of MSI was first described in 1977, when a research team combined a modified fundus camera with various interference filters to enhance theappearance of anatomical and pathological retinal features.1,2 However, this modified camera design was hampered by the use of filters and a bandwidth that was too wide, which resulted in diminished contrast and poor spectral separation.
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1. Oxy/deoxy map of a patient with myopic degeneration. Note the visualization of the choriocapillaris in the magnified image (right).
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Current, commercially available MSI devices, such as the RHA instrument (Annidis Health Systems), use multiple monochromatic LED-sourced wavelengths––ranging from 550nm to 780nm––to illustrate the individual anatomic components of the retina. Generally, shorter wavelengths are used to reflect anterior retinal features and longer wavelengths are used to reflect deeper retinal features, including the choroid.
RHA also has additional after-image processing that highlights oxygenated and deoxygenated hemoglobin, which may yield representation of metabolic activity (figure 1).3 This may allow the eye care practitioner to accent the retinal structures associated with arterial and venous blood by non-invasive means. One study described this process as a means of demonstrating oxygen saturation through morphological angiography.3
MSI in Clinical Practice
Today, MSI takes digital imaging to a new diagnostic level by yielding an enhanced view of the anatomical fundus layers. Separation of anatomical layers allows pathology-specific ophthalmoscopy and progressive views through the entire retina––from the internal limiting membrane to the choroid.
MSI is capable of creating a series of monochromatic, en face fundus spectral slices for added diagnostic insight. And, because conventional fundus photography is limited to parameters of the visible spectrum, it is less sensitive than MSI in detecting features that are reflected in the longer range of the spectrum such as deep retinal layers and the choroidal structures.
| Case Report: MSI Helps Confirm Diagnosis of VMTS |
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Fundus (left) and MSI shorter wavelength (right) images of our patient’s left eye reveal surface traction secondary to VMTS. Note the enhanced anatomical detail on MSI shorter wavelength.
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A 54-year-old white male presented with
signs of small-caliber drusen in his left eye that were evident with
fundus imaging.
Interestingly, his visual acuity measured 20/20 O.U. In
addition to fundoscopy, we performed multispectral imaging (MSI) and
spectral-domain optical coherence tomography (SD-OCT).
Both MSI and SD-OCT indicated the presence of vitreomacular traction
syndrome (VMTS). MSI shorter wavelength effectively captured the
topographical striations associated with the VMTS. Also, MSI further
identified an atrophic area associated with the decomposition of melanin
in the retinal pigment epithelium (RPE). On SD-OCT, we saw that the
photoreceptor integrity line was intact, which was why this
patient––with significant RPE atrophy––remained asymptomatic.
We recommended oral carotenoid supplements as well as an
AREDS-equivalent multivitamin. Additionally, we prescribed 1,000 IU
vitamin D daily to address the inflammatory nature of the pathology.
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Furthermore, MSI may help a managing clinician make a more informed diagnosis. The device aids in:
- Localization of retinal morphological abnormalities.
- Interpretation of disease, based upon affected layer.
- Enhanced viewing of obscure, subtle or overlapping pathological structures.
- Enhanced viewing of deep retinal structures.
Preventative eye care is predicated on early detection, and being able to identify risk factors and preliminary clinical signs is essential. MSI affords eye care providers the means to understand the anatomical aspects of specific pathologies, as well as perform further examination of vascular tissues, fluids and metabolic markers of retinal health and integrity. Ultimately, with increased use, MSI will help facilitate earlier and more accurate detection of many sight-threatening retinal conditions.
Thanks to Richard Maharaj, O.D., B.Sc., of Hamilton, Ontario, for contributing this column. Dr. Maharaj sits on the U.S. optometric advisory board for Annidis Health Systems, Inc.
1. Delori FC, Gragoudas ES, Francisco R, Pruett RC. Monochromatic ophthalmoscopy and fundus photography. The normal fundus. Arch Ophthalmol. 1977 May;95(5):861-8.
2. Ducrey NM, Delori FC, Gragoudas ES. Monochromatic ophthalmoscopy and fundus photography. II. The pathological fundus. Arch Ophthalmol. 1979 Feb;97(2):288-93.
3. Arimoto H, Furukawa H. Retinal blood oxygen saturation mapping by multispectral imaging and morphological angiography. Conf Proc IEEE Eng Med Biol Soc. 2007;2007:1627-30.