How wide-field SS-OCT expands spectrum of normal peripheral retina
Wide-field retinal imaging can be performed using a commercially available swept-source optical coherence tomography (SS-OCT) platform (DRI OCT Triton, Topcon) and only the internal fixation light for patient navigation provided detailed images of both normal and pathologic peripheral retinal findings.
Reviewed by Netan Choudhry, MD
Wide-field retinal imaging can be performed using a commercially available swept-source optical coherence tomography (SS-OCT) platform (DRI OCT Triton, Topcon) and only the internal fixation light for patient navigation provided detailed images of both normal and pathologic peripheral retinal findings.
“In 2016, we published a paper describing our experience with ultra-widefield Spectral-Domain OCT (SD-OCT) using a system with a 30° steerable lens (Spectralis, Heidelberg Engineering) [Ophthalmology. 2016;123(6):1368-74],” said Netan Choudhry, MD, founder and medical director, Vitreous Retina Macula Specialists of Toronto, Canada. “Recognizing that not all clinicians have access to that device, as a next step we expanded our work to investigate the wide-field imaging capabilities of a stationary device using the internal fixation light only.”
Their experience showed that montages assembled from single-line scans provided high quality images with excellent anatomic details and that correlated with published histopathological findings. Dr. Choudhry believed this approach has great potential value for clinical and research applications.
The feasibility and performance of wide-field SS-OCT was evaluated in an observational study that included 31 eyes of patients ages 18 to 85 years. All patients had previously diagnosed retinal findings that represented a broad spectrum of pathologies.
Common diagnosis
The most common diagnoses were rhegmatogenous retinal detachment, retinitis pigmentosa, choroidal folds, diabetic macular edema, and proliferative diabetic retinopathy. Other conditions included branch and central retinal vein occlusion, pachychoroid disease, choroidal granuloma, macular pucker, macular hole, myopic schisis, hydroxychloroquine maculopathy, exudative age-related macular degeneration, and vitreomacular traction.
The imaging was done by an experienced photographer. Eyes were dilated with phenylephrine 2.5% and tropicamide 1%, with one drop of each medication instilled three times at five-minute intervals, followed by a 20-minute dilation period. The internal fixation light was used to navigate the patient’s eye towards the periphery or to areas of interest seen on previous examination.
“The wide-field imaging technique using the internal fixation light only does not require movement of the patient’s head, but it is limited to use in well-dilated eyes and requires that the patient be able to fixate,” said Dr. Choudhry, also lecturer, Department of Ophthalmology & Visual Sciences, University of Toronto.
The scans were obtained at a rate of 100,000 A-scans/second in 12-mm fashion. In addition to evaluation of image quality, the montages created from the line scans were assessed for the degree and extent of peripheral retinal visualization, and they were registered to ultra-widefield, pseudocolor images obtained with digital scanning laser technology (200Tx, Optos).
Dr. Choudhry reported that the field of view achieved varied among the patients studied. The average field of view was 129° and the maximum was 169°. “In contrast, we could obtain a 230° field of view with our steerable laser that could be aimed in any direction,” Dr. Choudhry added.
Applications
Dr. Choudhry said the ability to visualize the peripheral retina combined with the imaging capabilities of SS-OCT creates opportunities to gain increased understanding of normal and pathologic features of the peripheral retina.
“This technique has utility for improving our knowledge of the anatomic spectrum of the normal peripheral retina and the natural history and evolution of normal and pathologic retinal findings,” Dr. Choudhry explained. “It also can enable insights into pathologic changes that occur with treatment of peripheral retinal diseases or in systemic diseases affecting the peripheral retina. In addition, the ability to image the peripheral retina could be helpful in telemedicine strategies for the evaluation and management of patients without access to retinal specialists.”
Netan Choudhry, MD
This article is based on a presentation Dr. Choudhry delivered at the 2017 Retina World Congress. Dr. Choudhry is a consultant to Topcon and a speaker and advisor for Optos.
