Stage II: round or curvilear full-thickness retinal defect (50%) or broken, the test is positive, suggesting a FTMH rather than pseudo- or lamellar hole. Stage I: yellow spot with loss of normal foveolar depression. Three percent (5 of 156) of eyes met a composite endpoint of 25% or greater decrease in relative central subfield thickening and 50 µm or greater decrease in CSMT at two consecutive time points, and 1% (2 of 156) of eyes exhibited increases in both measures by at least these amounts. The mean absolute change was a decrease in 13 µm (95% CI −17 to −8 µm). The mean change in relative central subfield thickening, defined to represent the change in excess retinal thickness, was a decrease of 6% (95% CI −9% to −3%) between the 8am and 4pm time points. 126 Two scans of adequate quality were obtained at each time point and sent to a reading center. In the largest study to date, 156 eyes of 96 participants with center-involved DME on ophthalmoscopy and CSMT of 225 microns or greater were evaluated at six time points between 8am and 4pm using the Stratus OCT. On average, retinal thickness in DME decreases slightly during the day, but the proportion of eyes with DME exhibiting clinically meaningful changes is small. Ferris III, in Retina (Fifth Edition), 2013 Diurnal variation of DME Macular oedema from diabetic retinopathy was more reliably detected with OCT and HRT II than with RTA ( Guan et al 2004, Goebel and Franke 2006). Hoffman et al 2005 found a moderate agreement on optic disc parameters between RTA, OCT and HRT II, but there were discrepancies between them. In order to obtain quantitative stereometric measurements, the examiner draws a contour line along the disc edge, which is used in follow-up visits to ensure accurate monitoring of subtle changes. Using edge detection analysis, the topography algorithm identifies the left border of the light, corresponding to the vitreoretinal surface, and calculates the disc topography. Using blood vessels as guidelines, registration software automatically overlays the map on the fundus image, enhancing reproducibility and measurement accuracy ( Fig. During scanning, the RTA acquires a red-free fundus image. Five such scans are obtained at the macula, three scans at the disc, and additional five scans cover the peripapillary area. A 3 × 3 mm scan consisting of 16 optical cross-sections is acquired within 0.3 seconds. The calculated algorithm distance between the two light peaks determines the retinal thickness at a given point. Due to the oblique projection of the beam and the transparency of the retina, the backscattered light returns two peaks corresponding to the vitreoretinal and the chorioretinal interfaces. The retinal thickness analyser projects a vertical narrow green helium-neon (543 nm) laser slit beam at an angle on the retina while a CCD camera records the backscattered light. Wolffsohn PhD PgC PgDipAdvClinOptom, in Ophthalmic Imaging, 2008 Retinal thickness analyser (RTA)
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