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T. Q. Kirk, N. G. Ghazi, A. S. Baras, J. S. Tiedeman, B. P. Conway; Errors in Automated Retinal Thickness Measurements by Optical Coherence Tomography in Neovascular Age-Related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2619.
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To report the frequency, type, and significance of errors encountered in optical coherence tomography (OCT) retinal thickness measurement (RTM) in patients with subfoveal neovascular age-related macular degeneration (SFAMD) treated with intravitreal bevacizumab.
A retrospective chart review of 46 eyes of 46 patients who received intravitreal bevacizumab for subfoveal neovascular AMD with OCT before and after treatment. All eyes underwent Stratus OCT imaging for RTM using fast macular acquisition protocol. All 6 line scans of each macular study were reviewed for error detection. Indicators of error included poor foveal centeration in 2 or more line scans, a foveal center thickness standard deviation-to-foveal center thickness ratio of greater or equal to 10%, a signal strength (SS) of less than or equal to 7 (suboptimal SS), edge detection kernel (EDK) misplacement in 2 or more line scans, and a "low" software confidence analysis. Caliper calculation of the thickness of both the central macular 1mm zone and the center foveal point was performed following standardized guidelines. These values were then compared with those generated by the software.
Errors in automated OCT RTM were found in 91% of eyes prior to treatment with bevacizumab and 72% of eyes after treatment (p=0.01). Suboptimal SS was the most common error indicator noted before and after treatment. Eyes with subretinal (SR) or subretinal pigment epithelial (SRPE) fluid were found to be at highest risk for error (100% and 90% of the eyes respectively). In such eyes, EDK misplacement was the most commonly encountered error (85% and 60% of the eyes respectively). The occurrence of this type of error was significantly reduced following treatment (38% and 35% respectively). In eyes with intraretinal fluid only, suboptimal SS was the most common indicator (50% of the eyes), and EDK error was significantly less frequently encountered than in eyes with SR fluid (31.2%; p=0.002). In eyes with EDK error, the average absolute difference between the caliper and software calculated thicknesses for the central 1mm zone and center point were 42+/-18 µm and 59+/-24 µm respectively, 95% C.I.
OCT errors in RTM occur frequently in SFAMD using the currently available analysis algorithms. These errors should be considered in OCT imaging involving patients with SFAMD. Eyes with SR or SRPE fluid have the highest likelihood for error, which may be reduced after treatment. Caliper calculation may provide a more accurate estimate of the true central macular thickness in such cases.
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