The International Widefield Imaging Study Group (IWISG)—a physician panel with expertise in retinal imaging—has released recommendations for classifications and guidelines for defining “widefield” and “ultra-widefield” imaging.
Field-of-view interpretation is subjective due to the different angles (external, internal) and clinician perception. The expert panel determined that the field of view should include the macula at the center. Field-of-view cut points for widefield and ultra-widefield should correspond to common anatomical features (Figure 1).
The expert panel defined “widefield” as a single capture image centered on the fovea, capturing the retina in all four quadrants posterior to and including the vortex vein ampullae. In contrast, the panel defined “ultra-widefield” as a single capture view of the retina in the far periphery in all four quadrants.
The expert panel developed new term, “panretinal,” to define a single capture, 360-degree, ora-to-ora view of the retina (Figure 2).
The panelists defined several other terms, including:
• Posterior pole: Retina within and just slightly beyond the arcades;
• Midperiphery: Region of retina up to the posterior edge of the vortex vein ampulla; and
• Far Periphery: Region of retina anterior to the vortex vein ampulla.
Optical coherence tomography (OCT) B-scans are primarily used for cross-sectional examination of the retina.
The expert panel found variances with OCT use; field of view was not always applied, and the OCT could include variable pixels and aspect ratios. To address these inconsistencies, the expert panel recommended that the description of the B-scan should include the size of the B-scan, the location, the scan time, and symmetry.
Further, to be considered “widefield,” OCT-angiography (OCT-A) images must capture the retina in all four quadrants and include the retina up to the posterior edge of the vortex vein ampullae. To be considered “ultra-widefield,” OCT-A images must capture all four quadrants beyond the anterior edge of the vortex vein ampullae.
In summary, the IWISG panel recommends basing definitions on anatomical landmarks to better reflect the clinical exam. The group also calls for improved inter-device consistency, the incorporation of montage into the image description for precision, and the incorporation of asymmetry in view into the description for all imaging modalities.
These recommendations should bring much needed uniformity to clinical exams, Dr. Choudhry said.