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J. Ho, D. P. E. Castro, L. C. Castro, Y. Chen, J. Liu, J. G. Fujimoto, J. S. Schuman, J. S. Duker; Clinical Assessment of Mirror Artifacts in Spectral Domain Optical Coherence Tomography Device. Invest. Ophthalmol. Vis. Sci. 2010;51(13):293.
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© ARVO (1962-2015); The Authors (2016-present)
This study investigates the characteristics of a spectral / Fourier domain Optical Coherence Tomography (SD OCT) image artifact known as the "mirror artifact". SD OCT detection produces images symmetrical about the zero delay line. Commercial instruments truncate one side of the image, leaving the remaining half for display. When retinal images cross the zero delay line, the symmetric mirror image on the truncated side will also cross into the scanning range on the displayed portion of the OCT image. Thus, the OCT image appears to be "folded" onto itself. This is known as the mirror artifact. The incidence of this artifact is calculated and correlated to spherical equivalent and central visual acuity (VA), and associated ocular factors and artifact severity are also analyzed.
Cirrus HD OCT Macular Cube 512x128 scans taken for a period of one year were analyzed for the presence of mirror artifacts. Severity of artifacts was analyzed by the degree of segmentation breakdown that it caused on the 5x5 macular map (graded from 1/5 to 5/5 of the map). A retrospective medical records review was conducted to note demographics, logMAR VA, ophthalmologic diagnosis, spherical equivalent, and cataract surgery. A random concurrent, comparative subset of patients without artifacts was selected for medical records review for comparison to artifacts group.
Out of the scans from 1,592 patients, 9.3% of the patient scanned (148 patients, 200 eyes) contained mirror artifacts. Significantly more myopic spherical equivalent (p< 0.001), worse VA (p< 0.001), longer axial lengths (p= 0.004) and higher proportions of mild/high myopia (p< 0.001) was found for patient with than without artifacts. Worse VA is associated with increased artifacts severity (p= 0.04).
A high incidence of mirror artifacts was found out of all scans analyzed. This artifact was highly correlated with increasing myopic spherical equivalent and worse VA. Improvements in imaging system design may be necessary to resolve this problem in mild/high myopic eyes. Operators should be advised to properly position the retina when scanning non-myopic patients.
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