AAO 2017 Retina Subspecialty Day: Imaging Session

Cindy Ung, MD
Ophthalmology Resident
Mass Eye and Ear

Dr. David Sarraf
kicked off the imaging session discussing new biomarkers of angiogenesis in AMD using OCT angiography (OCTA). He discussed that OCTA can show remarkable and significant change in type 1 neovascular membranes. In a study looking at type 1 neovascular lesions in 40 eyes, 80% of the eyes showed a mean increase of 0.3 mm in 1 year. He identified three growth forms of these neovascular lesions: immature, mature and hypermature. Immature neovascular lesions with a rosette of neovascular vessels or capillary fringes showed remarkable growth with doubling in area. Mature lesions with large vessel sea-fans showed modest, stable growth. Hypermature neovascular lesions with large straight vessels and a dead tree appearance showed inactive growth.

Dr. Jay Duker then gave us an update on the current status of swept source OCT (SS-OCT). He discussed the theoretical advantages of SS-OCT, which includes faster acquisition speed, wider scanning range, less sensitivity roll-off, which provides simultaneous imaging of the vitreous and choroid, and longer wavelength allowing for deeper penetration into the choroid. The disadvantages include increased cost, worse signal-to-noise ratio, and worse axial resolution. He discussed two commercially available SS-OCT devices on the market: Topcon: DRI (Deep Range Imaging) OCT Triton and the Zeiss: Plex Elite 9000. The caveat is these devices are expensive and not widely available yet.

Dr. Nadia Waheed then discussed wide-field OCTA and its application in retinal vascular disease. In comparison to widefield fluorescein angiography, wide-field OCTA has better resolution but is limited in its peripheral extent. One of the issues of imaging the far periphery with OCTA is peripheral distortion, which can cause a distortion of up to 12-20%. Once this distortion is accounted for, wide-field OCTA may revolutionize our ability to assess and quantify retinal vascular disease.

Dr. Richard Rosen presented the subclinical diabetic macular changes revealed by OCTA. He showed OCTA perfusion density maps of patients with non-proliferative diabetic retinopathy, proliferative diabetic retinopathy (PDR) and controls. He found that while there was no significant difference between controls and patients with NPDR, perfusion density was found to be greater in patients with PDR. This feature has the potential to be a useful biomarker for the development of diabetic retinopathy and may be used for longitudinal follow-up.

Dr. Philip Rosenfeld then discussed OCTA in the management of AMD and polypoidal choroidal vasculopathy (PCV). He highlighted several benefits of OCTA, including the detection of subclinical neovascular lesions. His study of 160 eyes with non-neovascular AMD showed that eyes with subclinical neovascular disease are at a 15-fold higher risk for exudation over 12 months than eyes without these subclinical lesions. Other highlighted benefits of OCTA included early detection of type 3 neovascularization, easier detection of PCV, exclusion of CNVM when drusen and fluid are present, and evidence that re-treatment is needed with anti-VEGF therapy even before obvious exudation recurs on structural OCT imaging. OCTA detects subclinical neovascularization in AMD long before exudation occurs and can thus help guide anti-VEGF therapy.

A new consensus definition and terminology for atrophy on OCT findings in the setting of AMD was then introduced by Dr. SriniVas Sadda. He introduced four new terms developed from the consensus group: complete RPE and outer retinal atrophy (cRORA) which has 4 criteria: (1) the presence of a region of hypertransmission of at least 250 μm in diameter, (2) a zone of attenuation or disruption of the RPE of at least 250 μm in diameter, (3) evidence of overlying photoreceptor degeneration, and (4) absence of an RPE tear; incomplete RPE and outer retinal atrophy (iRORA), complete outer retinal atrophy, and incomplete outer retinal atrophy.

Dr. Richard Spaide then discussed how disease expression in AMD is correlated with choroidal thickness. He found that extracellular deposits are highly correlated to choroidal thickness. In particular, soft drusen are associated with normal-thickness choroid while subretinal drusenoid deposits are more commonly found in eyes with thinner choroids. He highlighted a new entity called “pachydrusen” associated with greater choroidal thickness. These drusen are generally irregular in shape, often isolated, have a sharply defined border and are scattered across the posterior pole. Manifestations of AMD seem to be related to these drusen and if we analyze these drusen in their subtypes, we could potentially better identify disease-modifying genes.

New imaging findings in pathologic myopia were then discussed by Dr. Kyoko Ohno-Matsui. She introduced a new prototype of a wide-field SS-OCT device that allows for the 3D reconstruction of a posterior staphyloma image in the region of interest with a size of 20 mm x 14 mm and a depth of 5 mm. With this new OCT, it is possible to examine the entire extent of posterior staphyloma in highly myopic eyes. Widefield OCT shows promise to become an important tool in examining staphylomas.