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ED Gilmore; Relationship Between Eccentricity and Measurement Error of Retinal Thickness Using the Retinal Thickness Analyzer . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4357.
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Purpose:To assess intra-visit variability and inter-visit repeatability of retinal thickness measurements using the Retinal Thickness Analyzer (RTA) in clinically normal subjects. Methods: The sample comprised 10 clinically normal subjects of mean age 33 yrs (range 22-45 yrs). Each subject underwent a full macular RTA scan (i.e. using all 5 default RTA locations covering the complete macula) followed by 6 repeats of the foveally-centred and one other non-foveal scan (which was systematically varied between subjects). Only the thickness values derived from the foveally-centred and selected non-foveal scans of the initial 5 default scans were included in the analysis. Radially averaged thickness values, representing the average of all thickness measurements inside discrete radii, were used to reduce errors in alignment between scans. This methodology was used to facilitate the evaluation of both intra-visit variability and inter-visit repeatability of retinal thickness measurements. Results: Group mean absolute thickness values showed retinal thickness to be thinnest at the fovea (120.0 µm, SE 7.1 µm), thickest at 1000-1800 µm from the fovea (184.3 µm SE 7.2 µm) and then to decline with further increase in eccentricity. The individual COVs ranged from 0.03 to 0.24 (median value 0.09) for the central area (i.e. 0-200 µm from the fovea). Typically, the COV was highest at the fovea and improved (i.e. reduced) significantly with increase in eccentricity and was unchanged across the two visits. The COR for the central area was approximately 14.4 µm (relative to a mean effect of 120.0 µm) and was similarly highest at the fovea but improved with increasing eccentricity. Conclusion: The significantly higher COV and COR in the central region (0-200 µm) may, in part, be explained by the combined effect of the rapid rate of change of retinal thickness in this area, involuntary physiological eye movements and errors of alignment between successive images.
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