RGB: New Hues on the Block

The new UWF red/green/blue modality captures retinal images with natural color, enhancing diagnostic accuracy

Ultra-widefield (UWF) imaging is reshaping retinal diagnostics by providing comprehensive, high-contrast views of the retina. With the introduction of RGB (red/green/blue) imaging technology, clinicians can now capture more natural color representations, enhancing the detection of subtle retinal changes.

UWF imaging is defined by the Widefield Imaging Consensus group as a fovea-centered single (non-montaged) field of view capturing the retina beyond the vortex vein ampullae in all four quadrants.¹ Compared to traditional 30° to 50° fundus photography—or 75° with montaged Early Treatment Diabetic Retinopathy Study (ETDRS) Seven Standard Fields— UWF imaging provides greater visualization of the retinal periphery. This can be the earliest or the predominant site affected in several retinal diseases.²

UWF imaging, including UWF color fundus, autofluorescence (AF), optical coherence tomography (OCT), fluorescein angiography (FA), indocyanine green angiography (ICGA), and OCT angiography, continues to provide new insights on disease pathophysiology and prognostication and guides ophthalmologists in the early detection, accurate staging, and appropriate treatment of various retinal pathologies.^2,3

With short acquisition times and the ability to extensively image the retina through nonmydriatic pupils, UWF imaging is also a promising tool for tele-ophthalmological screening.⁴

UWF imaging technology

Among the currently available UWF imaging technologies, optomap imaging (Optos PLC; Dunfermline, UK) is based on confocal scanning laser ophthalmoscopy with an ellipsoidal mirror, and is capable of imaging 200° or 82% of the retina in a single capture, covering a greater retinal area in lesser time compared to other UWF cameras.^5,6 With the montaging of gaze-steered images, optomap coverage can be further extended to 220° or 97% of the retina for a nearly panretinal view.¹

Historically, Optos UWF devices utilized only monochromatic green (532 nm) and red (633 or 635 nm) laser scans to obtain pseudocolor RG (red/green) images that are characterized by a greenish hue due to the absence of a blue channel.⁵ ecently, the company introduced a color RGB (red/green/blue) imaging modality to its California device that can combine 635-nm red and 532-nm green laser scans with a 488-nm blue laser scan to obtain a composite image of the retina with a natural color representation similar to its appearance on fundoscopy.

The updated Optos California device obtains UWF RG and RGB images simultaneously, in addition to sensory red-free and choroidal images. The device is also capable of green and blue laser AF, as well as FA and ICGA.

UWF RG versus UWF RGB imaging: Initial results

At our clinic, optomap imaging is routinely used to assist in disease screening and treatment planning. Therefore, we were interested in assessing if this additional color UWF imaging capability translated to any additional benefits compared to clinically validated UWF RG imaging.

For this, we conducted what was the first qualitative comparison of images captured with the RG and RGB modalities of the Optos California device. One hundred seventy-two eyes of 86 patients were included in a retrospective study at the Retina Clinic London (United Kingdom). UWF RG and RGB image characteristics were compared in a range of retinal conditions.⁷

The RGB images were characterized by a more natural appearance of the optic nerve and the retina, with the nerve fiber layer and hyaloid reflection being more clearly visible compared to RG images.

This was expected, as short wavelength blue lasers better visualize the vitreoretinal interface and superficial retinal structures.⁸ Thus, subtle epiretinal membranes were more easily detected with RGB imaging.

Vitreous opacities and proliferative vitreoretinopathy (PVR) were more recognizable due to the natural color representation, while the superficial details and complete extent of retinal detachments were more easily visible [Figure 1].

The retinal periphery was more clearly visualized with higher contrast in RGB images, which facilitated the examination of vitreoretinal landmarks and subtle retinal holes, schitic changes and degenerations [Figure 2].

Early adopters of UWF RGB imaging have also described increased clarity and improved visualization of subtle details, as well as more natural color representations of ocular tumors.⁹

However, this was not to say that the RGB images were always superior. In specific disorders, we found RG and RGB images to better visualize different components of retinal lesions based on their depth in the retina. This is because long-wavelength red lasers can penetrate the deeper retinal layers and the choroid10 and intermediate wavelength green lasers better visualize the neurosensory retina,¹¹ while short-wavelength blue lasers scan the vitreoretinal interface and the superficial retina.

Thus, deep retinal and choroidal vessels in highly myopic eyes were more clearly visualized with RG images, whereas peripheral retinal atrophy could be better discerned in RGB images [Figure 3].

While drusen in age-related macular degeneration (AMD) were better characterized with the more natural colors of RGB imaging, areas of geographical atrophy and healthy retinal pigment epithelium (RPE) were better defined in RG images [Figure 4].

In diabetic retinopathy, RGB imaging provided high-contrast visualization of superficial retinal hemorrhages, ghost vessels and neovascularization, while RPE changes and deep retinal hemorrhages were better visualized in RG images. In neovascular AMD, retinal exudates were better demonstrated with RGB images, while RG images provided enhanced visualization of subretinal fibrosis [Figure 5].

Key Takeaways

In addition to the 635-nm red and 532-nm green lasers used in Optos ultra-widefield RG imaging, the new Optos color RGB modality also utilizes a 488-nm blue laser to obtain retinal images with more natural colors.
RGB imaging provides better contrast at the periphery due to the natural color representation of retinal holes and degenerations, while the short-wavelength blue laser better images the vitreoretinal interface and superficial retinal findings—such as proliferative vitreoretinopathy, epiretinal membrane, superficial retinal hemorrhages, and neovascularization.
In comparison, RG imaging better visualizes deeper retinal structures, such as retinal pigment epithelium changes, subretinal fibrosis, deep retinal hemorrhages, and choroidal vessels.
Ultra-widefield RG and RGB modalities have complementary imaging capabilities, with the adjustment of percentage laser wavelength composition in the OptosAdvance software allowing customization of image presentation for optimal visualization according to the depth of retinal lesions.

A peek into the future of retinal imaging

To summarize, UWF RGB images were characterized by more realistic color representations of the retina that provided greater contrast for the identification of subtle details. Our findings demonstrate that while the RGB modality can better image the vitreoretinal interface and superficial retinal structures, the UWF RG modality enhances the visibility of deep retinal or chorioretinal structures.

Thus, RG and RGB imaging were found to be complementary diagnostic methods. Clinicians may choose between both modalities according to the retinal layer to be visualized in each patient, which will allow accurate detection and objective monitoring of various vitreous, retinal or choroidal pathologies.

Using the integrated OptosAdvance software of the Optos California device, we were also able to manually adjust the percentage wavelength composition of the obtained images to enhance the visualization of different retinal structures. The real-world clinical utility of UWF RGB imaging and the ideal wavelength percentages for the optimal visualization of different retinal lesions will be interesting areas to explore in future studies.

We also anticipate that the clarity and natural appearance of UWF RGB images will improve image interpretability and reduce the rates of ungradable images in artificial intelligence-based automated detection of retinal diseases. In teleophthalmology, this will enable non-specialist health workers to more accurately identify referable cases, allowing for timelier diagnosis and treatment of potentially blinding diseases for improved patient outcomes.

Figures Legend

All figures courtesy of Ophthalmic Surgery, Lasers and Imaging Retina – Slack Journals. ⁷

Fig.1. Retinal detachment and vitreoretinal proliferation clearly visualized with more natural color representation on RGB (red/green/blue) imaging (A) than on RG (red/green) imaging (B).

Fig.2. Retinal hole, schitic changes and peripheral lattice degeneration are imaged with greater contrast on RGB imaging (A), while retinal pigmentation is better visualized on RG imaging (B).

Fig.3. Eyes with high myopia showing a more natural color representation of retinal atrophy on RGB imaging (A, C) and enhanced visualization of choroidal vasculature and laser retinopexy scars on RG imaging (B, D).

Fig.4. Age-related macular degeneration (AMD) lesions showed better characterization of drusens on RGB imaging (A, C), while retinal pigment epithelium (RPE) changes and transition between geographic atrophy and healthy RPE were better visualized on RG imaging (B, D).

Fig.5. Retinal exudates in neovascular AMD are more clearly visible on RGB imaging (A), while RG imaging better highlights subretinal fibrosis, visible as well-delineated, greenish bands (B).

Editor’s Note: A version of this article was first published in PIE Issue 33.

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