Optical coherence tomography (OCT) is a well-established imaging method in the ophthalmic practice. We describe a novel corneal topography method that directly measures anterior cornea surface elevation from a single en face OCT image. This method uses an OCT interferometer configuration equipped with a multiple delay element (MDE) in the reference arm. The MDE selects multiple axial positions within the target object, simultaneously, which leads to information from multiple axial distances to be cumulated in a single en face OCT frame. When an en face OCT scan of a cornea is acquired with such an OCT setup, the resulting image contains nonoverlapping circular contours. Images of a reflective metallic sphere obtained using this method are used to numerically calibrate the setup. Using these calibration results, position information contained in the en face images from the cornea can be measured directly obtaining three-dimensional coordinates for multiple points located on the cornea surface. From these points, the topographic map of the anterior cornea surface can be generated, using interpolation or Zernike polynomial decomposition. Experimental results of in vivo cornea topography obtained with this method are presented.
We have presented previously a novel method for the evaluation of the surface shape of an object, with
immediate application to measurement of cornea shape. This method uses single shot C-scans obtained by
using a multiple delay element (MDE) in the reference path of an OCT system. A calibrated MDE-OCT
system can be used to measure the elevation of points on the cornea, in contrast to existing methods
which are based on measurement of the cornea slope. The associated algorithm for extracting corneal
topography data points from the MDE-OCT C-Scan image will be presented, data points which can then
be used to calculate the Zernike coefficients for the cornea shape. The differences between the existing
systems and the MDE-OCT method for keratometry and corneal topography are discussed.
In a previous report<sup>1</sup> we presented a novel method using <i>en-face </i>OCT for the evaluation of the curvature of
an object, with immediate application to measurement of corneal curvature. This method relies on single
shot C-scans obtained from an <i>en-face </i>OCT system with a multiple delay element introduced in the
reference arm. In the present report we show how the same methodology can be used for the measurement
of the axial position of a spherical object. The theoretical basis and the accuracy of assessing the axial
position using this method are presented. The potential application of this method in the measurement and
tracking of the <i>in-vivo </i>axial position of the eye is also discussed.
A novel method is presented for the evaluation of object shapes. The method has applicability in the
measurement of the cornea curvature. An <i>en-face </i>OCT system using a multiple delay element in the
reference path of the interferometer is proposed. This method allows detection of the polar variations of
the cornea curvature from a single <i>en-face</i> OCT image. Inspection of multiple contours in the <i>en-face</i>
OCT image can also be used to estimate the instantaneous axial position of the eye.