Experience with en face OCT shows its value for following disease progression in wet and dry age-related macular degeneration and in diseases that disrupt the inner segment/outer segment/ellipsoid zone.
Reviewed by Philip J. Rosenfeld, MD, PhD
Take-home: Experience with en face OCT shows its value for following disease progression in wet and dry age-related macular degeneration and in diseases that disrupt the inner segment/outer segment/ellipsoid zone.
Philip J. Rosenfeld, MD, PhDMiami-En face optical coherence tomography (OCT) is a valuable imaging strategy for anatomic and angiographic viewing of the fundus. The technology is useful for diagnosing and monitoring diseases with layer-specific anatomic abnormalities or microvascular flow alterations, said Philip J. Rosenfeld, MD, PhD.
“The real advantage of en face OCT is the ability to slice and dice the images throughout their entire depth, from the choroid to the vitreous,” said Dr. Rosenfeld, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami.
“En face OCT imaging became clinically useful with the advent of high-speed, high-density, spectral domain OCT raster-scanning techniques,” Dr. Rosenfeld added. “It has come of age over the past decade, and we can expect its use in clinics will increase with further uptake of faster SD-OCT systems, swept source OCT systems, and developments in OCT angiography.”
En face OCT imaging with defined boundary segmentation was developed and patented by the Bascom Palmer Eye Institute and the University of Miami Miller School of Medicine and then licensed to Carl Zeiss Meditec. This license is now shared with Optivue.
Following disease progression
Dr. Rosenfeld said en face OCT imaging has been useful for following disease progression in wet and dry age-related macular degeneration (AMD) and in diseases that disrupt the inner segment/outer segment/ellipsoid zone, such as macular telangiectasia type 2 and any of the macular degenerations.
Geographic atrophy with reticular pseudodrusen (RPD) imaged with color fundus imaging, autofluorescence imaging, and infrared imaging compared with two difference en face OCT images extracted from the same dataset. The outer retinal slab en face OCT image shows the subretinal drusenoid deposits (RPD) while the sub-RPE slab highlights the geographic atrophy. (Figure courtesy of Philip J. Rosenfeld, MD, PhD)
En face OCT imaging of geographic atrophy (GA) harnesses the fact that there is hyper-transmission of light into the choroid below Bruch’s membrane in areas devoid of retinal pigment epithelium (RPE).
The most useful en face image is derived from the sub-RPE slab and uses the light that is reflected from the choroid in a given A-scan. Areas of GA have a distinct appearance with defined borders and the area of atrophy appears bright relative to surrounding intact RPE, Dr. Rosenfeld explained.
“An automated algorithm currently available on only one proprietary OCT device (Cirrus HD-OCT, Carl Zeiss Meditec) can segment and measure areas of GA,” he said. “With imaging of the photoreceptor/RPE interface, en face OCT is also useful for studying photoreceptor disruption around the edge of GA.”
Predicting where GA will extend
Dr. Rosenfeld noted these areas of photoreceptor outer segment disruption appear to predict where the GA will extend. En face OCT imaging is able to predict the direction of GA growth because it can assess the integrity of different retinal layers surrounding GA.
Similarly, based on the ability to identify outer retinal disruption, progression of macular telangiectasia type 2 has been predicted using en face OCT.
Outer retinal slab en face OCT image showing disruption of the area of phorotreceptor outer segment disruption with loss of the inner segment/outer segment/ellipsoid zone region as observed on the corresponding B-scan. (Figure courtesy of Philip J. Rosenfeld, MD, PhD)
This same outer retinal en face OCT image can also visualize reticular pseudodrusen, which are subretinal drusenoid deposits seen in eyes with AMD. Now, with high-speed, swept-source OCT widefield scans, both the GA and reticular pseudodrusen can be visualized with a high-density, single 12 x 12 mm scan.
Dr. Rosenfeld explained that OCT angiography is a variation of OCT en face imaging. It generates flow images by assembling multiple B scans from specific locations and provides information on flow and intensity.
Philip J. Rosenfeld, MD, PhD
This article is based on a presentation given by Dr. Rosenfeld at Retina Subspecialty Day during the 2015 meeting of the American Academy of Ophthalmology. Dr. Rosenfeld receives research grants from Carl Zeiss Meditec.