Clinical Update
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Retinal Imaging: Choosing the Right Method
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"It&#;s just going to keep getting better.&#; That&#;s how K. Bailey Freund, MD, summed up the state of retinal imaging. Perhaps Hermann von Helmholtz said something similar when he introduced the ophthalmoscope in . But he could not have imagined all that his Augenspiegel (eye mirror) has spawned.
Today&#;s devices can reveal all the layers of the retina. Several optical coherence tomography (OCT) devices include color fundus photography capability. And there&#;s a device that takes images and lasers the eye. &#;All the manufacturers are going in the direction of multiple capabilities in one device,&#; said Dr. Freund, at Vitreous-Retina-Macula Consultants of New York. He called retinal imaging &#;a hot field, with a lot of advances occurring very quickly.&#;
Though Dr. Freund is not worried yet about being replaced by a machine, he and other retina specialists agree that imaging has changed the way they identify pathology and monitor response to therapy. It has expanded their view, as well as their understanding, of disease mechanisms and manifestations.
&#;Imaging has revolutionized the management of patients with retinal disease,&#; said Jay S. Duker, MD, at Tufts University. Although OCT may come first to mind, he said, other modalities in the armamentarium keep retina specialists busy debating the relative merits of each.
OCT has changed clinical practice and opened new areas of understanding.
In practice. OCT is very good at measuring thickness of the retina, so it&#;s helpful for diseases that cause fluid buildup, such as retinal vein occlusion (RVO) and diabetic macular edema (DME), said Dr. Duker. &#;In , you can&#;t treat diabetic macular edema or wet age-related macular degeneration (AMD) without an OCT. It&#;s standard of care for treatment of those diseases.&#;
OCT allows evaluation of different levels of macular ischemia not previously seen with prior imaging modalities. &#;Traditionally, we appreciated only superficial capillary ischemia. But newer OCT and high-resolution systems (resolution down to 3 µm from 10 µm) have revealed an intermediate and a deeper plexus that can also be ischemic. We never appreciated that clinically,&#; said David Sarraf, MD, at Jules Stein Eye Institute, UCLA.
A new window on disease processes. OCT has revealed previously unknown pathology, said Dr. Freund. For example, &#;OCT really helped us understand how macular holes occurred. It made us realize that we were not very good at determining whether fluid was in or beneath the retina. It&#;s helped me understand wet macular degeneration by pinpointing the location of the abnormal new vessels.&#; Are they beneath the RPE, in the subretinal space, or proliferating in the retina itself? This delineation of anatomic subtypes of neovascularization, known as types 1, 2, and 3, respectively, has influenced Dr. Freund&#;s treatment choices.
OCT has revealed the following:
Advantages. OCT is noninvasive, reproducible, and easy to interpret, Dr. Duker said. Dr. Sarraf added that it requires neither dye injection nor the bright lights used for color fundus photography, so it&#;s easy on patients.
Downside. OCT doesn&#;t identify blood well, so it won&#;t document or measure a disease with bleeding in the retina, Dr. Duker said.
On the horizon. Most U.S. practices use spectral-domain OCT, said Dr. Freund, noting that the next wave will include swept source OCT (SS-OCT), which is commercially available outside the United States. SS-OCT allows deeper penetration of tissue and faster acquisition. By capturing enhanced depth images of the choroid, SS-OCT deepens our understanding of central serous chorioretinopathy, which is characterized by a thicker-than-normal choroid, he said. Beyond that, Dr. Freund foresees that adaptive optics will be incorporated into OCT.
In addition, OCT is being studied as a possible tool for large-scale screening of asymptomatic patients for conditions including glaucoma and DME.
A typical fundus camera delivers a 50-degree field of view, but now ultra-widefield imaging systems can deliver 100 degrees or more. Dr. Freund said two systems are now commercially available in the United States that do ultra-widefield imaging.
Optos 200Tx. Using scanning laser ophthalmoscopy, the Optos 200Tx can image the peripheral retina to 200 degrees with single capture. And because it can produce both FA and FAF images, it&#;s becoming more popular among retina specialists, Dr. Freund said. Dr. Sarraf added that it requires no special lenses or dilation.
However, both doctors noted a caveat: The image is created by red and green scanning lasers that produce inaccurate color (pseudocolor), which may limit its interpretation. Further, said Dr. Sarraf, various artifacts may be present, including those caused by the eyelashes or the nose. He said that it&#;s possible to digitally match peripheral images to create a color montage for greater resolution and a better appreciation of the true nature of the disease.
Spectralis. Heidelberg Engineering offers an add-on lens for the Spectralis camera to capture an ultra-widefield view. The add-on is interchangeable with the existing lenses. It has FA and ICGA capability, but not FAF. It is designed to detect and monitor clinically relevant peripheral changes such as microaneurysms, neovascularization, perivascular leakage, or areas of nonperfusion, said Dr. Freund.Color fundus photography captures 30- to 50-degree views of the retina and optic nerve. &#;Virtually every ophthalmologist in the country has a fundus camera,&#; Dr. Duker said. &#;It&#;s widely available, easy to use, and is very good at documenting the appearance of the optic nerve and existence of blood buildup in the eye.&#; But, he added, &#;We rarely make treatment decisions based on the photos.&#;
What&#;s new? Although today&#;s cameras deliver high resolution, color fundus photography hasn&#;t undergone any major transformations since the s, Dr. Sarraf said. More recent developments include enhanced capabilities for creating color montage photographs of the posterior pole and periphery with automated software.
Fluorescein angiography. FA has been around since the s. It&#;s good at finding focal lesions to laser. But ever since anti-VEGF therapy supplanted focal laser treatment, &#;focal identification of the lesion is not as important as it once was,&#; Dr. Duker said. &#;Many of us still use fluorescein when first making the diagnosis of wet AMD.&#;
Dr. Sarraf agreed that standard FA is a good baseline tool for fine-tuning the diagnosis of choroidal disorders and neovascular macular degeneration.
A wider view. Ultra-widefield angiography captures 100 to 200 degrees to the periphery and beyond the equator, revealing pathology such as neovascular proliferation or ischemia that can&#;t be identified with standard angiography, Dr. Sarraf said. He uses it to guide laser treatment in diabetic retinopathy and RVO, where lesions extend beyond the macula to the periphery. Other uses include imaging tumors, choroidal melanoma, and some hereditary diseases.
Indocyanine green angiography. ICGA has a more limited role than FA in the clinic, said Dr. Sarraf, noting some of the differences between the methods: In ICGA, the dye is much more protein bound than fluorescein, so less leakage is visible on the angiogram. In addition, the longer wavelength can better penetrate the RPE and blood. As a result, ICGA complements FA, which captures images of retinal circulation above the level of the RPE.
Uses of ICGA include the following:
Fundus autofluorescence. FAF is not yet in widespread use, although it has gained traction over the last decade and, in some cases, may replace the more invasive fluorescein angiography, said Dr. Sarraf. If you&#;re using FAF, Dr. Freund noted, it&#;s important to know that different systems employ different wavelengths. Heidelberg uses a short blue wavelength; the Optos a longer green wavelength.
Uses include the following:
Dr. Sarraf. In a patient who has transitioned from dry to wet macular degeneration, my practice guideline is to obtain a baseline color fundus photo and baseline fluorescein angiogram, along with SD-OCT, to determine if the neovascularization is type 1, 2, or 3, which can influence the prognosis and the aggressiveness of the therapy. Going forward, I use only OCT to judge response to therapy.
Dr. Freund. Don&#;t rely exclusively on OCT printouts. Sometimes you&#;ve acquired hundreds of scans, but the printout shows maybe two. You need to understand the limitations of the automated algorithms. You may misinterpret the results if you don&#;t look at individual scans on the monitor
Dr. Duker. OCT is going to become increasingly important in the practice of ophthalmology from front to back. Angiography will become increasingly less important because OCT will be able to do some&#;or perhaps all&#;of the things that angiography does. Finally, there&#;s a place for autofluorescence in a referral practice.Regardless of the advances in imaging, the experience of a skilled clinician is still essential in fundus examination, for example, in assessing the health of the disc and identifying peripheral retinal tears and detachments, Dr. Sarraf said. And unlike the exam, no machine can &#;give a sense of comfort and satisfaction to the patient.&#;
But these sophisticated systems have enhanced clinical practice. &#;Our understanding of retinal and macular disease is much more clearly defined,&#; Dr. Sarraf said. And there&#;s more to discover. &#;There&#;s always mystery involved in the retina.&#;
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Jay S. Duker, MD, is director of New England Eye Center and professor and chairman of ophthalmology at Tufts Medical Center, Tufts University School of Medicine. Financial disclosure: Receives research support from Carl Zeiss Meditec; is a consultant to Alcon/Novartis, Allergan, EMD Serono, Optos, Regeneron, and Thrombogenics; and holds stock in Eye-Netra, Hemera Biosciences, and Ophthotech.
K. Bailey Freund, MD, is a member of Vitreous-Retina-Macula Consultants of New York and clinical associate professor of ophthalmology at New York University School of Medicine. Financial disclosure: Consults for Bayer HealthCare, Genentech, Heidelberg Engineering, and Regeneron.
David Sarraf, MD, is clinical professor of ophthalmology in the Retinal Disorders and Ophthalmic Genetics Division at Jules Stein Eye Institute, University of California, Los Angeles. Financial disclosure: Is a speaker for Heidelberg and has an investigator grant with Regeneron.
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The Academy&#;s downloadable Retina Informed Consent Video Collection (#V) includes 21 short videos&#;each about five minutes long&#;on specific, common retinal conditions. OMIC-reviewed, each video clearly explains risks and benefits to enhance patient understanding, encourage consent, improve compliance, and set realistic expectations to mitigate malpractice risk.
The collection of 21 retina topics (provided in both English and Spanish) is $545 for Academy members, $709 for nonmembers. Choose from a variety of file formats.
To see video clips and order, visit the Academy Store.Since , iCare has been innovating how optometrists and ophthalmologists visualize, monitor, and manage sight-stealing conditions, including glaucoma and retinal diseases like diabetic retinopathy, age related macular degeneration, and geographic atrophy. Since introducing the first rebound tonometer 20 years ago, they have added the iCare EIDON family, iCare DRSplus, and the iCare COMPASS perimeter. These retinal imaging devices and the fundus-driven perimeter establishes iCare as a trusted partner to ophthalmologists, optometrists, and physicians passionate about fast and reliable diagnoses.
With the iCare EIDON product family , iCare has proven that it has advanced beyond tonometry with the first TrueColor Confocal system for high-resolution, ultra-widefield imaging. The advantage of TrueColor Confocal technology is the detail-rich images captured using white LED light to provide superior color fidelity while confocal imaging blocks scattered light for sharper, more informative images with greater contrast.
In , iCare received FDA 510(k) clearance for the EIDON Ultra-Widefield Module , which combines high-definition image quality with a 200° view of the retina. Specifically, the Ultra-Widefield Lens Module can capture 120° images of the retina in a single shot or up to 200° with the expanded SmartMosaic function.
For more information, please visit weiqing.
When the Ultra-Widefield (UWF) Lens Module is used with iCare EIDON devices, it provides clear visibility into the periphery. Because it enables the acquisition of ultra-widefield color, infrared, autofluorescence, and fluorescein angiography images, eyecare providers (ECPs) have come to trust and rely on the iCare EIDON system of products for optimal patient care, ease of use, and workflow efficiency&#;with the added benefit of 200° panoramic view.
Combining the best of scanning laser ophthalmoscopy (SLO) systems with those of standard retinal imaging, the iCare EIDON product family delivers excellent image quality, sharpness, and detailed resolution. With automation and increased patient comfort, the UWF Module extends the view of the retina up to 200.°
iCare DRSplus is an easy-to-use and intuitive imaging system that requires minimal staff training to obtain high-quality images. This TrueColor Confocal Technology promotes detailed 45° retinal images and allows scanning through media opacities. Additionally, the field of view increases to 80° using the Mosaic feature. iCare DRSplus is designed to optimize patient comfort while improving workflow and clinical efficiency.
A confocal scanning laser ophthalmoscope can be used for several retinal imaging modalities, including fluorescein angiography, indocyanine green angiography (ICG), fundus autofluorescence and optical coherence tomography (OCT).1 The technology leverages horizontal and vertical mirrors to scan distinct layers of the retina while a confocal aperture blocks non-image-forming light to minimize scatter and chromatic aberration.2
Monochromatic laser illumination together with a confocal optical system produce high-contrast, detailed images due to the fact that illumination is solely provided by a laser beam and the remainder of the patient&#;s pupil is available for light collection. The laser also delivers a narrow wavelength band for more efficient excitation of fluorescence than the filtered flash illumination of a traditional fundus camera.2
TrueColor Confocal Technology is the next level for image quality as it delivers increased sharpness, better optical resolution and greater contrast. Unlike other technologies, it preserves image quality even in the case of media opacities&#;including cataracts&#;and can work with pupils as small as 2.5mm&#;eliminating the need for dilation.
iCare imaging and perimetry devices combine a TrueColor Confocal optical engine with a true white light LED source&#;which includes the entire visible spectrum of light. As a result, the entire retina is illuminated and captured. The result is TrueColor retinal images characterized by colors that represent the actual appearance of the retina.
In contrast, traditional fundus cameras use a flash lamp with a broad spectrum illumination. In the absence of confocal optics, the reflected signal is derived from all tissue levels in the beam of the flash of light, and light scattering anterior and posterior to the plane of interest can greatly influence the detected signal.3
In iCare devices, white LED illumination provides high-quality, TrueColor images.This differs significantly from other imaging systems that combine different colored lights to create an artificial white light. Other features available with each iCare imaging device are stereo viewing, RGB channels and IR. The red-free filtering enhances visualization of retinal vasculature, the blue channel provides an improved view of the RNFL, the red channel allows visibility into the deep layers of the retina, and the infrared light provides detailed information about the choroid.
Many diseases that affect ocular health and threaten blindness first display pathology in the periphery, making early detection of abnormalities crucial to safeguarding patient health and well-being.
Diabetic retinopathy (DR), age-related macular degeneration (AMD), geographic atrophy (GA) retinal vein occlusions, (RVO), retinopathy of prematurity (ROP), and uveitis are chronic, progressive diseases that may first show signs in the periphery of the retina. Therefore, in these instances where early diagnosis is key to effective disease management and successful outcomes, images of the periphery are of utmost importance.
Currently, there is still no one, single test that can be used to diagnose these degenerative diseases. While structural analysis can be performed with fundus photos or optical coherence tomography imaging (OCT), other leading ultra-widefield imaging systems compromise resolution of posterior pole and may miss important vascular abnormalities or indications of retinal diseases. Conventional flash fundus cameras capture color images that are oversaturated in the red channel and washed out in the green and blue channels, resulting in a retinal picture that often looks flat and overly red.4
Using proprietary iCare software, doctors are able to compare images side by side in order to monitor pathology and disease progression over time with features that allow users to zoom in and out on an image. However, because some differences over time are so subtle, the software now harnesses the power of Flicker technology to give users even more information. Flicker technology enables images to be superimposed over each other so eyecare professionals can better visualize the change in pathology and disease progression over a given period of time. In addition to providing more granular information about fine details, this feature can also be used to educate patients about their eyes and help engage them in their treatment.
In a study that evaluated differences in acquisition time, peripheral extension, and chromaticity between three different commercialized ultra-wide-field (UWF) fundus cameras, the iCare EIDON FA with the UWF module demonstrated the lowest variability of acquisition time (9.5 s), compared to ZEISS Clarus (25 s) and Optos Silverstone (38.5 s).5
A statistically significant difference was found in the RGB distribution between each of the three devices (p&#;<&#;0.001). iCare EIDON demonstrated an average barycenter position (RGB&#;=&#;[0.412, 0.314, 0.275]) that represented the best color balance of the image. ZEISS Clarus had a noticeable red shift at the expense of the blue and green channels (RGB&#;=&#;[0.515, 0.294, 0.191]). Optos Silverstone showed an absence of the blue channel (RGB&#;=&#;[0.621, 0.372, 0.007]) which results in a distortion of the color of the image.5 Overall, the researchers concluded that the iCare EIDON provided more color-balanced retinal images with greater richness of color content than the other two devices.
The iCare COMPASS brings visual field analysis to the next level by combining Automated Tracked Perimetry&#;including an active retinal tracker&#;with TrueColor Confocal imaging. This ensures an accurate match between structure and function and informs diagnoses while reducing motion artifacts. By pairing structure with function, providers can unlock more details that lead to better disease diagnosis as well as more accurate patient monitoring.
Real-time retinal tracking actively compensates for eye movements during the visual field test for more accurate results. Additionally, the device is designed for patient comfort by allowing for natural blinks without impeding the data or results. For example, defects are delineated precisely as motion artifacts are reduced.
The iCare COMPASS perimeter is designed for a high correlation between retinal sensitivity values and retinal structure. This means that patient results will be informative about the structure and functionality of the retinal for better accuracy and patient monitoring.
While retinal imaging combined with confocal technology can provide a wealth of information on the retina's structure, this information is even more powerful when paired with functional analysis that delivers a more complete assessment of a patient's vision.
Timely detection of glaucomatous progression is crucial in the delivery of glaucoma care, and event-based analysis like visual field tests can be incredibly valuable when predicting overall visual function6 and when monitoring glaucomatous patients. While images can provide insight into structural changes in the optic nerve and retinal nerve fiber layers, glaucoma progression can also be observed as increasing functional loss in a series of visual fields.7
Also called standard automated perimetry, (SAP), visual field tests commonly deliver sensitivity measurements in the form of light flashes at 52 test points (for 24-2) stimuli. Recent improved testing algorithms like the Swedish interactive thresholding algorithm (SITA) and the availability of progression detection software like guided progression analysis (GPA) and visual field index have solidified SAP as the preferred method for diagnosis and follow-up of functional visual field loss.8
A study that analyzed structural and functional progression of glaucoma by fundus photography and visual field tests of 249 subjects revealed that in patients with manifest glaucoma, progression was detected first in the visual field test in 163 eyes (52%) in the optic disc first in 39 eyes (12%), and in one eye it was found simultaneously in both fundus photos and visual field progression.9
Other assessments of normative databases of commercial devices used to assess visual fields showed that a large proportion of ganglion cells must be lost before a visual field defect can be detected on SAP. Conversely, later in the disease process, the opposite tends to hold true where incremental losses in ganglion cells result in detectable declines in visual function before they can be visualized by imagery.10
Most eyecare providers agree that in order to adequately detect and monitor progression of glaucoma and retinal disease, retinal imaging and fundus perimetry are both critical to providing optimal patient care.
The iCare COMPASS enhances practice efficiencies due to the dual capabilities of combining a visual field test with retinal imaging all in one platform. It is easy-to-use, does not require a trial lens and allows remote viewing for patient education. Traditional SAP is typically performed through refractive correction with trial lenses, which can increase examination time and may cause artifacts. The iCare COMPASS removes this road block with its automatic refractive correction system with auto-focus.
Remote Viewer software offers embedded capabilities for network connectivity, for both remote data review and data backup. The iCare COMPASS Remote Viewer is a browser-based software that allows for reviewing from any network computer on the same local area network (LAN).
Additionally, the Remote Viewer provides image comparison tools, anatomic measurements, and intuitive post-processing tools. For example, images taken at different times can be registered and superimposed using Flicker technology to facilitate detection of morphological changes over time.
For the first time ever in a visual field test, iCare COMPASS delivers 60° confocal images of the retina in different modalities: TrueColor, infrared, and red-free.
The iCare COMPASS also leverages a new SmartMosaic feature to enable acquisitions of high-definition TrueColor images from the posterior pole to the periphery and creation of a seamless 100° montage.
The SPA report shows structural and functional changes over time. Progression assessment, rate, and prediction reliably evaluates disease stage in glaucoma management.
1. An overview of 2 baseline exams and the last follow-up
2. The Threshold Deviation map
3. The Progression Event Analysis, which is an estimation of visual field loss
4. The Global Trend Analysis, which is an expected loss over 3-5 years
5. Cluster MDs deviation and trend, for 24-2 and 30-2 grids
6. Pointwise Trend Analysis with progression rate
The ZEST Fast is a new threshold strategy to decrease exam time and boost efficiency. When compared to ZEST, this threshold is 30% faster in glaucoma patients and 40% in healthy patients.
While structural analysis can be performed with fundus photos or optical coherence tomography imaging (OCT), traditional instruments can be expensive and time-consuming. In some cases, technicians are required to take multiple images to eliminate views with eyelashes and to accommodate for blinks.
Other retinal imaging systems can be uncomfortable for patients who may be sensitive to a bright flash or have to contort themselves to &#;fit&#; in the machine. iCare overcomes these obstacles with their product line that allows eyecare professionals to choose the device that works best for them.
The agility of the iCare products mean doctors can see more patients per day OR perform the test alone for enhanced workflow efficiency. In addition, the iCare EIDON FA does not need an experienced retinal photographer, and the fully automated device eliminates the need for specialized training.
The iCare family of products offers fully automated devices that deliver comprehensive assessments. As a result, doctors gain a more informative view of the retinal health and disease progression in an easy-to-use, patient-friendly format.
For more information, please visit Laser Retinal Imaging.