OCT, FAF, MPOD and more for monitoring patients with macular degeneration.
These advanced non-invasive imaging tools are a safe, efficient and cost-effective way to gain additional information not otherwise seen during clinical examination.
Offering an in-depth analysis of retinal tissue, SD-OCT/OCTA has long been used in the management of patients with AMD. The high resolution and fast image acquisition coupled with the ability to dynamically view cross-sectional scans of the retina aids in the diagnosis and management of AMD. OCTA is a newer, non-invasive imaging technique that acquires angiographic information without the use of dye. This system gives information about structural and functional blood flow movement within the retina and choroid by using a unique motion detection technique.
Optovue AngioVue and ZEISS Angioplex are two commercially available OCTA systems. The AngioVue software of the Avanti Widefield OCT uses a split-spectrum amplitude deccorelation algorithm and scans at 70,000 A-scans per second in 3.0 seconds. AngioVue automatically segments vasculature into superficial and deep inner retinal plexuses, outer retina and choriocapillaris. This segmentation system is useful for detecting, localizing and classifying choroidal neovascular membranes (CNVM) found in wet AMD cases. OCTA allows for early detection of CNVM by examining the outer retinal area between the outer plexiform layer (OPL) and Bruch’s membrane.
Fundus autofluorescence (FAF) is a valuable, non-invasive tool that details the health of the retinal pigment epithelium (RPE). FAF instruments, such as the Canon CR-2 PLUS AF Digital Non-Mydriatic Retinal camera, use a specific wavelength of light absorbed by lipofuscin within the RPE cells, creating a “fluorescence” appearance of the retina. In early and intermediate AMD, FAF can be used to detect sub-clinical alterations in the RPE, allowing for earlier diagnosis and treatment of the disease.
It is important for clinicians to be able to identify and interpret fluorescence patterns to determine the status and prognosis of the disease. A normal, healthy fundus exhibits a diffuse homogenous autofluorescence with a decrease in autofluorescence when approaching the fovea. In early AMD, large soft drusen typically appear as defined areas of hyperfluorescence. Small and medium drusen are harder to detect and can present as a normal fluorescence pattern. Reticular photodrusen are important entities to identify as they are highly associated with disease progression. Photodrusen typically appear as multiple, small, oval areas of hypo-autofluorescence surrounded by normal autofluorescence. FAF is also used in identifying and detecting progression of geographic atrophy, which appears as an area of hypo-autofluorescence on FA.
Although all three types of CNVM can have a variable appearance on FAF, many studies have reported common FAF characteristics for each type. A classic (type I) CNVM is often characterized by an area of hypo-autofluorescence with a thin halo of hyper-autofluorescence. An occult (type II) CNVM often shows irregular intensity with multiple areas of hypo-autofluorescence. Retinal angiomatous proliferation (type III) CNVM typically shows discrete, uniform hypo-autofluorescence.
Standard automated perimetry (SAP) instruments, such as the Humphrey Field Analyzer from Carl Zeiss Meditec, Inc. or the Octopus 900 from Haag-Streit, have frequently been used to monitor central vision in AMD patients. The Octopus offers a central 10° static Macula field test and has the ability to analyze progression using the EyeSuite Progression Analysis. Unlike Humphrey and Octopus, Goldman perimetry uses kinetic testing and is performed by an experienced perimetrist.
When compared to standard automated perimetry, short wavelength automated perimetry (SWAP) has been shown to have increased sensitivity in detecting early AMD changes with a decrease in sensitivity as AMD advances.
QuantifEye MPS II from EyePromise is a computerized device that measures macular pigment optical density (MPOD). There is a strong association with decreased MPOD and the development and progression of AMD. MPOD testing allows proper recommendation for ocular vitamin supplementation in the early stages of AMD. A recent meta-analysis study revealed that lutein, zeaxanthin and meso-zeaxanthin supplementation improved MPOD both in patients with AMD and healthy subjects.
Scanning Laser Ophthalmoscopy (SLO) is a relatively new imaging technique producing high image resolution, improved contrast and enhanced penetration through ocular media, particularly cataract formation.
CenterVue has two products that adopt the confocal technology of SLO systems but use a white LED to guarantee true color images. This new technology has the benefit of combining SLO and Fundus camera capabilities. The Compass from CenterVue is a commercially available SLO device also offering both anatomy and function analysis by including an automated perimeter using a real-time retinal tracker.
The Eidon, another commercially available device from CenterVue, offers a true color widefield confocal view of the retina with excellent image quality and resolution. This instrument has the capability of combining autofluorescence with the Eidon AF. SLO infrared imaging is a useful feature in detecting sub-clinical structural changes in the macula seen in the early stages of AMD.
Other retinal cameras to consider: Marco’s AFC-330 features three-dimensional (x-y-z) automatic alignment, to capture clear images in very little time. The camera also includes automatic 3D stereo imaging, auto-panoramic imaging and external photography.
Daytona and California from Optos offer optomap the only clinically validated, ultra-widefield, retinal image. Only optomap captures up to 200° or 82% of the retina in a single image, according to the company. Using a green laser, optomap af captures images that allow for visualization of the metabolic changes in the retinal pigment epithelium to identify areas that may be at high risk for AMD and other ocular disease. OO
Leticia Rousso, OD, is an instructor at Nova Southeastern University in Fort Lauderdale, FL.
WHERE TO FIND IT:
800-970-7227 | USA.Canon.com
Carl Zeiss Meditec, Inc.
800.342.9821 | Meditec.Zeiss.com/USA
408.988.8404 | CenterVue.com
800.787.5426 | Haag-Streit-USA.com
800.874.5274 | Marco.com
800.854.3039 | Optos.com
866-344-8948 | Optovue.com