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R. A. Leitgeb, T. Schmoll, C. Kolbitsch, T. Le, A. Stingl; Corneal Microstructure and High-Fidelity Bowman-Layer Extraction Using Ultra-High Resolution FDOCT at 100.000 Scans/Sec. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3682.
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© ARVO (1962-2015); The Authors (2016-present)
To measure precise 3D corneal microstructure and topography with ultra-high speed and resolution and to provide high fidelity thickness maps of corneal subsurface layers as a prerequisite for exact planning of refractive surgery as LASIK.
Fourier domain optical coherence tomography (FDOCT) employing a Ti:Sapph laser with large bandwidth of 160nm allows for a resolution in tissue of less than 3µm. This bandwidth is imaged onto a high speed CMOS detector with 100.000 A-scans/second. Such speed is a prerequisite for reducing motion artifacts, which is of prime importance if precise anatomy is to be determined. Our main task is to extract corneal epidermal thickness and the Bowman layer thickness from within a measured 3D volume with high precision. Refraction at the cornea front surface will cause deviations of the OCT map from the true geometry. We correct for refraction in the full 3D volume by applying Snells law to each measured point at the cornea surface. The true geometric thickness of epidermis and the Bowman layer is then extracted from this corrected structure along the calculated surface normal.
High-speed corneal tomograms have been recorded at an A-scan rate of 100.000 scans per second. A full volume of 1000 x 100 x 800 pixels is recorded in only 1 sec exhibiting an axial resolution of less than 3µm. The Bowman layer boundaries could be extracted with better accuracy than the actual resolution since only the peak position was needed. We achieved a precision of 1µm. In a successive step thickness maps of different corneal subsurfaces are determined using a 3D refraction correction algorithm based on Snells law. Previous tomography systems of anterior chamber structures suffer from motion artifacts. We measured healthy corneas of different volunteers with high reproducibility, which was only possible with our realized high-speed acquisition.
We produce precise thickness maps of cornea substructure using a high performance FDOCT system with unprecedented imaging speed of the anterior eye anatomy. Such high performance system will eventually help to precisely plan refractive surgery such as LASIK with the availability of high fidelity 3D corneal microstructure.
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