Abstract
Conventional imaging of the human cornea with optical coherence tomography (OCT) relies on telecentric scanning optics with sampling beams that are parallel to the optical axis of the eye. Because of the shape of the cornea, the beams have in some areas considerable inclination to the corneal surface which is accompanied by low signal intensities in these areas and thus an inhomogeneous appearance of corneal structures. In addition, alterations in the polarization state of the probing light depend on the angle between the imaging beam and the birefringent axis of the sample. Therefore, changes in the polarization state observed with polarization-sensitive (PS-) OCT originate mainly from the shape of the cornea. In order to minimize the effects of the corneal shape on intensity and polarization-sensitive based data, we developed a conical scanning optics design. This design provides imaging beams that are essentially orthogonal to the corneal surface. Thus, high signal intensity throughout the entire imaged volume is obtained and the influence of the corneal shape on polarization-sensitive data is greatly reduced. We demonstrate the benefit of the concept by comparing PS-OCT imaging results of the human cornea in healthy volunteers using both scanning schemes.
Highlights
The human cornea shows a layered structure which was studied in vitro by various different approaches like histology [1], electron microscopy [2] and X-ray scattering [3,4,5,6] and is well known today
The aim of this work was to introduce a conical scanning optics design that enables scanning of the cornea with a large field of view (FoV) and perpendicular incident angles onto the corneal surface in order to enhance the signal intensity in the paracentral region and to reduce the influence of the corneal shape on PS-optical coherence tomography (OCT) data
We demonstrated a conical scanning optics design for imaging the human cornea in vivo, which produced good signal quality over the entire recorded area of the cornea because the sampling beam is almost perpendicular to the corneal surface throughout the FoV
Summary
The human cornea shows a layered structure which was studied in vitro by various different approaches like histology [1], electron microscopy [2] and X-ray scattering [3,4,5,6] and is well known today. The outmost layer, the corneal epithelium, is separated from the stroma by Bowman’s layer. The stroma itself is composed of about 200 stacked lamellae organized parallel to the surface. Each of those lamellae has a thickness of 1.5 μm to 2.5 μm and contains highly organized parallel collagen fibrils which subtend large angles with fibrils in adjacent lamellae. The backside of the cornea is delimited by the Descemet’s membrane and the corneal endothelium [7]. Various corneal diseases such as keratoconus lead to changes of this regular structure
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