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Humberto Ruiz-Garcia, Ramsudha Narala, Emma McDonnell, Florian M. Heussen, SriniVas R. Sadda; Comparison Of Choroidal Visibility And Thickness Measurements Using Two Spectral Domain Optical Coherence Tomography Instruments With Different Wavelength Light Sources. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2861.
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To evaluate the effect of spectral domain optical coherence tomography (SD-OCT) light source wavelength (840 nm vs 1050 nm) and B-scan averaging on the visibility and thickness measurements of the choroid.
Fifty eyes of 31 patients with a broad range of ocular pathologies, underwent volume raster scanning without B-scan averaging and high-definition raster scanning with frame averaging (4x) using the Cirrus HD-OCT (Zeiss Meditec, Dublin CA, 840 nm light source) and a prototype OCT instrument from Zeiss operating at 1050 nm. Using the digital caliper tool in the Cirrus review software, choroidal thickness at the foveal center was measured from the external side of the retinal pigment epithelial band to the choroid-sclera junction. Cases in which the full extent of the choroid (i.e. to the choroid-sclera junction) could not be visualized were noted and partial thickness measurements to the extent of the visible choroid were made. All eyes were measured by two independent, masked observers, and discrepancies were resolved by open adjudication. Choroidal thickness measurements and the percent of cases with full choroidal visibility were compared between devices and scanning protocols. Choroidal thickness measurements were also correlated with age and best corrected Snellen visual acuity.
The mean age of the patients was 65 years (range= 21 to 100 years), and 48% (n=15) were women. The choroid was fully visible in 60% (25/42) of eyes by non-averaged 1050nm SDOCT imaging, in 40% (17/42) by non-averaged 840nm SDOCT, in 82% (36/44) by averaged 1050nm SDOCT, and in 61% (27/44) by averaged 840nm SDOCT. Mean choroidal thickness did not differ significantly between eyes with fully or partially visible choroids. Univariate regression identified a linear relationship between age and choroidal thickness when measured using the averaged 1050nm scans (r=-2.48, p=0.005), but no relationship was found between choroidal thickness and visual acuity.
The use of a longer wavelength light source (1050nm) than the conventional wavelength (840nm) used in commercially available SD-OCT instruments allows for deeper penetration and improved visualization of the choroid. The enhanced visualization effect appears to be additive to other enhancement strategies such as B-scan averaging.
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