3D refraction correction and extraction of clinical parameters from spectral domain optical coherence tomography of the cornea

Abstract

Capable of three-dimensional imaging of the cornea with micrometer-scale resolution, spectral domain-optical coherence tomography (SDOCT) offers potential advantages over Placido ring and Scheimpflug photography based systems for accurate extraction of quantitative keratometric parameters. In this work, an SDOCT scanning protocol and motion correction algorithm were implemented to minimize the effects of patient motion during data acquisition. Procedures are described for correction of image data artifacts resulting from 3D refraction of SDOCT light in the cornea and from non-idealities of the scanning system geometry performed as a pre-requisite for accurate parameter extraction. Zernike polynomial 3D reconstruction and a recursive half searching algorithm (RHSA) were implemented to extract clinical keratometric parameters including anterior and posterior radii of curvature, central cornea optical power, central corneal thickness, and thickness maps of the cornea. Accuracy and repeatability of the extracted parameters obtained using a commercial 859nm SDOCT retinal imaging system with a corneal adapter were assessed using a rigid gas permeable (RGP) contact lens as a phantom target. Extraction of these parameters was performed in vivo in 3 patients and compared to commercial Placido topography and Scheimpflug photography systems. The repeatability of SDOCT central corneal power measured in vivo was 0.18 Diopters, and the difference observed between the systems averaged 0.1 Diopters between SDOCT and Scheimpflug photography, and 0.6 Diopters between SDOCT and Placido topography.

Extended scan depth optical coherence tomography for evaluating ocular surface shape

“…A linear least square circular curve fitting of the field curvature was used to obtain D, as described in previous studies. 28,31 In our system, D was 363.5 mm in the horizontal scan and 584.1 mm in the vertical scan, which was quite close to the ideal telecentric illumination condition. This nontelecentric quantization was used to correct ocular surfaces by employing Eqs.…”

“…The axial motion of the eye can be at least 25 μm over this period, 42 which may add to the error for the measurement. As previous studies pointed out, the axial eye motion can be corrected or reduced by developing algorithms for postprocessing the image, 31 or applying the technique with ultra high speed imaging. 43,44 In summary, we demonstrated a method for ocular surface shape measurement using the anterior segment SD-OCT. Algorithms were developed to automatically segment the ocular surface.…”

“…27 Recently, OCT has been used to quantitatively measure the biometry of the anterior ocular segment. [28][29][30][31] We have now developed a new custom-built SD-OCT with extended scan depth to measure the ocular surface shape and enable the evaluation of contact lens fitting. This instrument can image the entire ocular surface, including the cornea, limbus, and sclera.…”

OCT-based crystalline lens topography in accommodating eyes

“…However, the cornea and the crystalline lens surfaces are non-rotationally symmetric, therefore 3-D measurements are required. Recently, OCT combined with dedicated image processing algorithms provide accurate 3-D corneal [30,[38][39][40] and lens [28] surface reconstructions after distortion correction.…”

Anterior Eye Imaging with Optical Coherence Tomography

“…Very high performance anterior segment OCT systems have already been demonstrated in research centers [18,20,22,[106][107][108][109]. The performance of commercial anterior segment OCT will also improve as the cost of implementation drops and clinical application grows.…”