Optical distortion correction in Optical Coherence Tomography for quantitative ocular anterior segment by three-dimensional imaging

Abstract

A method for three-dimensional 3-D optical distortion (refraction) correction on anterior segment Optical Coherence Tomography (OCT) images has been developed. The method consists of 3-D ray tracing through the different surfaces, following denoising, segmentation of the surfaces, Delaunay representation of the surfaces, and application of fan distortion correction. The correction has been applied theoretically to realistic computer eye models, and experimentally to OCT images of: an artificial eye with a Polymethyl Methacrylate (PMMA) cornea and an intraocular lens (IOL), an enucleated porcine eye, and a human eye in vivo obtained from two OCT laboratory set-ups (time domain and spectral). Data are analyzed in terms of surface radii of curvature and asphericity. Comparisons are established between the reference values for the surfaces (nominal values in the computer model; non-contact profilometric measurements for the artificial eye; Scheimpflug imaging for the real eyes in vivo and vitro). The results from the OCT data were analyzed following the conventional approach of dividing the optical path by the refractive index, after application of 2-D optical correction, and 3-D optical correction (in all cases after fan distortion correction). The application of 3-D optical distortion correction increased significantly both the accuracy of the radius of curvature estimates and particularly asphericity of the surfaces, with respect to conventional methods of OCT image analysis. We found that the discrepancies of the radii of curvature estimates from 3-D optical distortion corrected OCT images are less than 1% with respect to nominal values. Optical distortion correction in 3-D is critical for quantitative analysis of OCT anterior segment imaging, and allows accurate topography of the internal surfaces of the eye.

OCT 3-D surface topography of isolated human crystalline lenses

“…The distortions present in this surface arising from the scanning architecture of the OCT system (fan distortion [37]) and the refractive index of the preservation medium were corrected. The other two surfaces visible in the OCT image were the second surface of the lens (posterior in anterior-up images and anterior in posterior-up images) and the cuvette.…”

“…We have presented recently a quantitative 3-D OCT system which allows profilometry of the ocular surfaces of the eye [36,37]. This technique was used for measurements of corneal elevation maps in vivo [38], biometry and lens alignment [39], dynamic measurement of crystalline lens radii of curvature with accommodation [20] and crystalline lens surfaces elevation maps in vivo [40].…”

Three-dimensional OCT based guinea pig eye model: relating morphology and optics

“…In previous works we have reported 3-D anterior segment biometry in human eyes in vivo, including anterior and posterior corneal and lenticular surface elevation maps [12][13][14][15][16][17], interocular distances along well identified axes [18] and full crystalline lens, beyond the margins of the pupil [19]. Quantitative analysis is possible by correction of distortions (fan, arising from the scanning architecture; optical, due to the refraction in the optical surfaces) and new automatic image processing algorithms that have allowed quantification.…”

Correction of image distortions in endoscopic optical coherence tomography based on two-axis scanning MEMS mirrors

“…Most distortion correction algorithms are based on a point-to-point mapping method [9][10][11]. Although this method is universal, it needs a complicated mapping process and can only be applied after the original interferogram data are converted to the structural image [12]. Applying this method to correct scanning distortion will consume a lot of computing resource and can hardly approach real-time display.…”