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N. Hutchings, C. Hyun, A. Mishra, K. Bizheva, T. Simpson; Accuracy and Repeatability of Ultra-High Resolution Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5685.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the accuracy and repeatability of optical thickness measures of an ultra-high resolution optical coherence tomographer (UHR-OCT) using an appropriate refractive index phantom as a gold standard.
The custom, high-speed UHR-OCT operating in the 1µm spectral range was used to obtain two-dimensional images of a series of phantom lenses. The UHR-OCT system provides resolution of 3.2µm (axial) and 10µm (lateral) in corneal tissue and image acquisition rate of 47,000 A-scan/s. The corneal phantoms were a series of 22 custom-made rigid contact lenses (Plano power; BCOR 8.60mm) with refractive index 1.376 (±0.0005 @589m; Optical Polymer Research, Inc., Gainesville, FL, USA). The central thickness of the lenses ranged between 104-764µm, measured using a precision mechanical gauge (Vigor GA-715; Japan). For each rigid lens, 10 2-D images (1000 A-scans x 512 pixels) were obtained. An automatic segmentation algorithm was used to determine the optical thickness of the glass phantoms from the UHR-OCT tomograms. All values of optical thickness were obtained as an average of 200 A-scans in the central section of the 2-D image. Accuracy was assessed using Deming regression, correlation coefficients and Difference vs Means plots. Method comparison and repeatability was assessed using intraclass correlation coefficients (ICC).
The optical and physical thickness measurements were almost perfectly correlated (Bootstrapped ρ=0.998). Accuracy The mean difference between the physical and optical thickness was -0.467±3.50µm. The UHR-OCT optical thickness tended towards very slightly smaller values for physical thickness measures less than 400µm and very slightly larger values for thickness' >400µm. Deming regression optical-physical thickness slope was 0.99±0.001. Repeatability ICCs were close to 1.0 for agreement between multiple measures of the same phantom. Method comparison exhibited a mean difference between the highest and lowest repeated measure of -0.23±0.09µm.
Our protype UHR-OCT is an accurate and repeatable device under optimal circumstances. On the basis of these estimates, it is anticipated that human corneal morphometry will be accurate.
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