AMD diagnostic imaging

Swept-source optical coherence tomography angiography (SS-OCT-A) can identify asymptomatic neovascularization in eyes with non-exudative AMD and patients are unaware they have a ticking time bomb in their eyes , according to Philip Rosenfeld MD, PhD, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami, US. The Dr Rosenfeld cited research going back as far as the 1970s where histopathological data showed cases of choroidal neovascularization in post-mortem eyes that were assumed to have dry AMD. Subsequent studies using ICG angiography conducted in the 1990s showed evidence of plaques and hot spots in eyes of patients with dry AMD in which the fellow eye had wet AMD, and those eyes with palques had a higher rate of exudation compared with eyes without plaques. He described recent anecdotal cases fitting the same pattern. One case involved an 85-year-old man with neovascular AMD in one eye. He responded to anti-VEGF therapy, while the left eye had stable non-exudative AMD. But only three weeks later the patient returned with significant vision loss and apparent exudation in the ‘stable’ eye. “We wanted to know what was going on. Did the choroidal neovascularization (CNV) develop suddenly, or was it present the whole time?” said Dr Rosenfeld in a presentation at the annual meeting of the American Society of Retina Specialists in San Francisco.

Patients are unaware they have a ticking time bomb in their eyes

ICG angiography Why not use ICG angiography to follow patients? That approach is expensive, invasive, time consuming, resource intensive, and until recently, such cases didn't have an intervention, he noted. Rather, Dr Rosenfeld and colleagues used a novel swept source OCT angiography system to look for subclinical CNV. The prototype from Carl Zeiss Meditec performed a 3mm X 3mm rraster scan centered on the fovea and repeated each B-scan 4 times, with 300 A-scans per B-scan, and 300 B-scan positions, for a total of 360,000 A-scans. Using a special decorrelation algorithms, the B-scans were compiled to provide en face flow images of the retina and choroid. The optical microangiographic approach known as OMAG provided provided the microvascular flow information and different layers were segmented, which included the whole retina, the inner or superficial retina layer or plexus, the middle or deep retinal plexus, and the outer avascular retinal layer. Another layer from the outer retinal layer to the choriocapillaris, known as the ORCC layer, was also created since this is where most of the choroidal neovascularization can be found. Subsequent clinical research (Ophthalmology, Roisman et al, Volume 123, Issue 6, 1309–1319) confirmed that the system could detect CNV lesions before they started leaking. Subsequent follow-up of 103 patients with wet AMD in one eye and dry AMD in the other revealed a prevalence of about 18% for these subclinical lesions, with an estimated rate of conversion to exudation of about 16% at one year, but longer follow-up is underway. “This is a new stage of non-exudative AMD. We call it non-exudative neovascular AMD. I think we can find these patients easily with SS-OCTA and we need to follow them closely. Ongoing studies are looking at prevalence, incidence, and onset of exudation. For now, in addition to close follow-up, we do not recommend anti-VEGF treatment,” he concluded. “I never treat asymptomatic patients. I educate my patients, I emphasize the need for vision monitoring at home, and I enlist them to be stewards of their own vision. In addition, if we start treatment in the absence of fluid, what’s our endpoint?,” Rosenfeld stated. prosenfeld@med.miami.edu