High-Resolution Imaging is the Cornerstone of Early Detection of AMD

The comprehensive dilated exam drives technology choice when diagnosing, differentiating, and following retinal conditions.

By Jim Williamson, OD, FAAO, FORS

With its longstanding use in posterior segment diseases, imaging technology has taught us most of what we know about the natural history of retinal conditions and continues to inform optimal management strategies. The pivotal studies of laser treatment to photodynamic therapy to anti-vascular endothelial growth factor for the treatment of age-related macular degeneration (AMD) were based on color fundus photographs.^1-4 Today, we have advanced technology like optical coherence tomography (OCT) with both multispectral and enhanced depth imaging (EDI) options, and fundus autofluorescence (FAF) that allows visualization of the entire posterior pole of the eye from the internal limiting membrane through to the choroid.

The Basics of Early Detection
What we see on dilation during a comprehensive patient exam should drive our use of OCT imaging. This advanced diagnostic tool is complementary to our clinical acumen. When we identify something of concern during the exam, OCT is indispensable for further evaluation. Drawing upon the entirety of the evidence and our subsequent interpretation, we are able to reach a definitive conclusion regarding a patient’s condition.

My preferred examination includes MultiColor in combination with OCT. MultiColor highlights retinal layers acquired with three simultaneous laser beams at different depths of the ocular fundus (Figure 1). This has become invaluable to me for the early detection of dry AMD. For example, subretinal drusenoid deposits or SDDs (formerly called reticular pseudodrusen) are difficult to detect clinically but can be easily visualized via the infrared (preferred) or blue wavelength (Figure 2). These deposits are a well-known risk factor for progression to geographic atrophy (GA)⁵ and can be highlighted with blue FAF and infrared imaging.

The ability to view subtleties of the retina in vivo with high-quality, high-resolution scans is comparable to the use of an MRI to view thin slices of the brain. If I suspect a patient has early AMD, I will order a 24-line or higher radial scan centered on the fovea, as well as a posterior pole dense scan, and an FAF. In my opinion, the traditional 5-line raster scan does not provide enough detailed information and gives the clinician a false sense of normalcy in an otherwise potentially diseased macula. The FAF will detect any areas of GA, and the infrared image—which is automatically taken with the OCT scan—will catch the presence of SDDs.  Later as the disease progresses (which it will) and I suspect a conversion to wet AMD, I run a high-resolution OCT angiography (OCTA) or, less commonly, perform a fluorescein (FA) and/or indocyanine green angiogram (ICGA).  When taken together, my OCT device allows me to simultaneously capture both side-by-side with one picture (Figure 3) which is a game-changer for comparative analysis. I can also change the default capture picture to either the FA or ICGA and set the OCT-B scan directly over any area of interest.

Key OCT Platform Features
When looking for AMD-related changes, having the ability to perform FAF is imperative. Using my OCT device (SPECTRALIS, Heidelberg Engineering), I can track areas of GA over time (Figure 4)—more important now that we have a treatment with pegcetacoplan, the first FDA-approved treatment for the dry form of AMD. Many patients with noncentral GA present with no symptoms, yet they have a disease that will likely progress centrally within a matter of years. Education becomes crucial for them to understand and accept their diagnosis. The platform’s movie mode incorporates all previous FAF images into a time-lapsed video that offers both patients and providers powerful visual evidence of GA progression.

In retinal conditions, we know it is critical to detect and track even the smallest amount of change over time. The automatic TruTrack active eye tracking capability allows me to summate up to 100 B-scans, producing micron-quality images for analysis. Since AMD patients often struggle to fixate due to their age, these features are paramount to obtaining usable data and informing individualized treatment plans.

An often-overlooked aspect of determining if a patient does in fact have AMD versus another disease process is evaluating the choroid. Using the enhanced depth imaging (EDI) option when searching for AMD-like changes helps to avoid misdiagnosis (Figure 5). One example is patients with pigmentary changes and a thick choroid who often present with pachychoroid spectrum disease versus a drusenoid degeneration such as AMD. I recently saw such an example in my practice: an EDI OCT on an older patient who had been diagnosed with unilateral intermediate AMD and placed on AREDS2 supplements revealed a choroidal thickness of more than 400 µm indicating pachychoroid-related disease.

Conclusion
Multimodal imaging is a critical tool in early detection of AMD. Technology of course must be combined with what we see with our own eyes during the clinical exam. Patient education should not be overlooked. I believe in spending time with all patients to educate them—not only those with AMD—about health risks and the importance of eating healthy, exercising, maintaining an optimal weight, and controlling systemic disease.

Once patients enter the intermediate AMD stage, we can offer AREDS2 supplements. At-home AMD monitoring system has been shown to improve outcomes once a patient converts to the wet form of the disease,⁶ providing another vision-saving tool.

All of our diagnostic strategies work synergistically, giving information that allows us to formulate an appropriate plan and follow-up schedule. It is most important to remember that AMD is just that, a degeneration. Each tool has its own strength and plays a role throughout different stages of the disease.

Jim Williamson, OD, FAAO, FORS, is the residency supervisor at the Memphis VAMC and Secretary for the Optometric Retina Society. He may be reached at [email protected].

Reference

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2. Bressler NM, et al; Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in age-related macular degeneration with verteporfin: two-year results of 2 randomized clinical trials-TAP report 2. Arch Ophthalmol. 2001;119, 198-207. PMID: 11176980.
3. Rosenfeld PJ, et al; MARINA Study Group Ranibizumab for neovascular age-related macular degeneration. N Engl J Med. 2006;355:1419–1431. doi: 10.1056/NEJMoa054481.
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