New technology takes invisibility cloak off in retinal imaging
New imaging technologies, such as ultra-wide-field fluorescein angiography and optical coherence tomography angiography, are providing more details about retinal diseases than previous imaging technologies, leading to better understanding of disease processes.
Reviewed by Royce W. S. Chen, MD
New imaging technologies are now available that have changed the way retina specialists evaluate patients, revealing structures that previously could not be visualized.
This increased diagnostic capability provided by ultra-widefield fluorescein angiography (FA) and optical coherence tomography angiography (OCTA) allows physicians to go where they could not previously go in the detection and treatment of retinal diseases.
Ultra-widefield FA
There are primarily two non-contact, ultra-widefield FA diagnostic units available–the Spectralis Ultra-Widefield Angiography Module (Heidelberg Engineering), which provides 102-degree retinal images, and the Optomap fa (Optos), which provides 200-degree retinal images, according to Royce W. S. Chen, MD. In both cases, the viewing capabilities outstrip their conventional counterparts, which offer images ranging from 30 to 50 degrees of the retina.
Ultra-widefield technology offers substantial advantages over conventional FA, Dr. Chen pointed out. Dr. Chen is the Helen L. and Martin S. Kimmel Clinical Assistant Professor of Ophthalmology, Columbia University Medical Center, New York.
“Ultra-widefield FA can capture a larger area of the retina in one frame compared with standard FA,” Dr. Chen explained. “It is advantageous to be able to visualize both the posterior pole and the peripheral retina at the same moment in time.
Figure 1. This ultra-widefield FA image shows diffuse capillary leakage, dark spots of hypofluorescence, and areas of complete capillary dropout in the periphery encroaching on the macula that led to the diagnosis of ischemic central retinal vein occlusion. (Images provided by Royce W. S. Chen, MD)
“Previously, when several images had to be montaged together, there was a time difference between when the images were obtained,” he added. “In some patients who were more challenging to image with standard field FA, views of pathologies in the peripheral retina are now more easily obtainable.”
Some cases presented
He demonstrated the efficiency of ultra-widefield FA in the case of an 80-year-old male with a sudden decrease in visual acuity. Upon presentation, visual acuity was 20/400 in the right eye.
The “dramatic” FA image showed diffuse capillary leakage, dark spots of hypofluorescence, and areas of complete capillary dropout in the periphery encroaching on the macula that led to the diagnosis of ischemic central retinal vein occlusion.
“This technology has been very helpful in obtaining a better sense of the overall health of the eye,” Dr. Chen said.
Figure 2: Here is an ulta-widefield FA and OCTA image of a patient with birdshot with a choroidal neovascular membrane. OCTA offers superior details of different vascular layers of the retina that previously were not available by other imaging devices. (Images provided by Royce W. S. Chen, MD)
A corresponding spectral-domain OCT (SD-OCT) image of the same case showed extensive macular edema present. Treatment consisted of regular intravenous injections of aflibercept (Eylea, Regeneron) and the visual acuity levels have remained stable at 20/100.
Dr. Chen also outlined the usefulness of ultra-widefield FA in cases of diabetic retinopathy, sickle cell retinopathy, and birdshot chorioretinopathy.
In the case of sickle cell disease, ultra-widefield FA has been extremely helpful. In the case of an 18-year-old male, the bilateral visual acuity was 20/20. “The ultra-wide FA technology captured the temporal border of the retina very well and showed the abrupt transition from the vascular to the avascular retina,” Dr. Chen reported.
Arteriovenous anastomoses and arterial occlusions were also visible. These patients are usually asymptomatic, he pointed out. Ultra-widefield FA allows physicians to learn more about the status of the peripheral retina and how the disease progresses, even in pediatric patients.
Dr. Chen relies on ultra-widefield FA when examining patients with uveitis. “This imaging is very useful to determine the level of disease activity, whether there is vasculitis in the more peripheral retina or in the more posterior retina, which suggests more active disease,” he said. “It can visualize areas of ischemia, cystoid macular edema, blockage from granulomatous or other uveitic lesions, choroidal neovascularization, and even the presence of floaters in the vitreous.”
OCT angiography
This iteration of OCTA is based on SD-OCT platforms. An algorithm is used to detect blood flow as a contrast medium and repeatedly sample sections of the macula. “This technology is very interesting and exciting in retina,” Dr. Chen said.
There are a few advantages of OCTA compared with FA. First, the former is not invasive and no fluorescein dye (with its potential for allergic reactions) is injected into the patient.
Second, OCTA offers superior details of different vascular layers of the retina that previously were not available by other imaging devices. The technology allows segmentation of the retina and the potential to detect changes and review them after the patients have undergone imaging.
Dr. Chen outlined a case of sickle cell retinopathy in a patient. Despite the absence of visual symptoms, vascular changes can be taking place in the retina. An OCTA from this case showed the presence of subtle vascular changes in the macula.
A flow void was visible with lack of circulation. A corresponding OCT image shows thinning in the temporal macula, suggesting that a vascular event occurred in that area in this asymptomatic patient.
Perhaps the greatest advantage, according to Dr. Chen, is that OCTA provides a great deal of quantitative information.
“We can skeletonize the vascular images and quantify the actual vascular density,” Dr. Chen said. “We can also look at the foveal avascular zone and its irregularity to better understand the changes in these patients.”
Newer imaging technologies continue to redefine and refine physicians’ approach to complex retinal diseases, Dr. Chen concluded.
Royce W. S. Chen, MD
Dr. Chen has no financial interest in any aspect of this report. This article was adapted from a presentation that Dr. Chen delivered at the Precision Ophthalmology 2016 meeting.
