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Charles Wu, T Keith Brock, Michael H. Chen; Comparing field of view in ultra-widefield fundus imaging. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1565.
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© ARVO (1962-2015); The Authors (2016-present)
ISO standards for field of view (FoV) exist for traditional fundus images (FI) which are based on a circular region of fundus, with the cornea as the reference. Since ultra-widefield fundus imaging (UWFI) captures non-circular images, and uses different reference points to define FOV, measurements can vary by up to 1.5x. For this reason an alternative definition is desirable.
14 eyes from 8 patients were scanned on both the CLARUS™ 500 (ZEISS, Dublin, CA) and the California af (Optos, Marlborough, MA) The primary outcome was to quantify the number of fundus quadrants visible in a FI. The quadrant was defined as “visible” if at least 50% of the vortex vein ampullae (VVA) was observed in the UWFI. The analysis utilized the green-free channel to accentuate the choroidal layer and was conducted by trained clinicians. In the event that a definable VVA was not detected in a quadrant, a square was drawn with the corners overlying existing detected VVA. If the free corner was clearly visible on the fundus image, the scan was given credit for effectively imaging that quadrant (Figure 1).
On average, the ZEISS CLARUS 500 was found to image 3.36 out of 4 VVA, while the Calirofnia af could image 2.57 out of 4. A more detailed analysis was performed when a VVA was not observed in a quadrant. This analysis revealed that the CLARUS 500 instrument effectively imaged all four quadrants in 13 out of 14 eyes (93%). Optos imaged all four quadrants in 1 out of 14 eyes (7%). This analysis can also be presented as a ratio of the total number of quadrants seen versus the total number of quadrants. In this analysis, the CLARUS 500 instrument imaged 55 quadrants of 56 possible quadrants (98%). The Optos instrument imaged 36 quadrants of the possible 56 quadrants (64%).
The data of this study supports the conclusion that the CLARUS 500 instrument is not as vulnerable to artifacts as are other UWFI platforms. Advanced analysis, in the absence of fundus anatomical landmarks, demonstrates that the CLARUS 500 instrument consistently images all four quadrants in an overwhelming majority of cases.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Figure 1. Determining visibility of each quadrant in UWFI using VVA. (TOP) 50% ampullae visibility(BOTTOM) Advanced analysis with lack of landmarks
Figure 2. Vortex vein ampulla analysis
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