Direct corneal elevation measurements using multiple delay en face optical coherence tomography

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.