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Ryan P. McNabb, Francesco LaRocca, Sina Farisu, Anthony N. Kuo, Joseph A. Izatt; Distributed Scanning SDOCT of the Anterior Segment for Quantitative Corneal Power Measurements. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1749.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal topography is currently the primary method for clinically assessing corneal shape and power but utilizes information from only the anterior surface. Anterior segment SDOCT images both surfaces and is thus independent of assumptions underlying topography such as the absence of prior refractive surgery. A major limitation to SDOCT biometry is corruption by patient motion during volumetric data acquisition. We have developed a novel approach of distributed scanning SDOCT (DS-SDOCT) based on high-speed distribution of individual A-scans across the cornea, thus encoding patient motion into high spatial frequencies which are removed by spatial filtering.
Five eyes of five adult subjects were imaged with topography, Scheimpflug photography, and DS-SDOCT under an IRB approved protocol. DS-SDOCT data was acquired using a commercial SDOCT system with =840nm, Δ=50nm, 10 kHz A-scan rate and a telecentric scanner in the sample arm (Bioptigen, Inc.). The portable telecentric scanner was mounted on a modified slit-lamp base with a chin and forehead rest for subject stability. A custom waveform was applied to the galvanometer scanners for high-speed distribution of A-scans in a "daisy" shaped pattern across the central 6mm of the subject’s cornea. The measured corneal powers obtained from DS-SDOCT acquisition were compared to results from topography (Atlas, Zeiss) and Scheimpflug photography (Pentacam, Oculus).
Average corneal powers measured from five eyes using topography, Scheimpflug, and DS-SDOCT were 43.80±1.46, 43.70±1.30, and 43.67±1.45, respectively. Using the average of topography and Scheimpflug photography as the gold standard, the RMS errors against the gold standard were 0.204, 0.204, and 0.387 D for topography, Scheimpflug, and DS-SDOCT.
DS-SDOCT appears to correct for patient motion sufficiently to allow for total corneal power measurement consistent in both magnitude and standard deviation with standard techniques. RMS errors for DS-SDOCT were only slightly higher than that for the techniques which comprised the gold standard. DS-SDOCT may provide an alternative to standard techniques for corneal biometry in patients with altered corneas.
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