Recent Advances in Corneal Imaging

Recent Advances in Corneal Imaging

A. Elbita (Bradford University, UK), R. Qahwaji (Bradford University, UK), S. Ipson (Bradford University, UK), T. Y. Ahmed (Bradford University, UK), K. Ramaesh (Bradford University, UK) and T. Colak (Bradford University, UK)
DOI: 10.4018/978-1-60960-477-6.ch016

Abstract

This chapter details work with sequences of corneal images from a confocal microscope to develop enhancement methods to improve the visual quality of the images. Due to involuntary movements of the subject’s eye during image capture, the images suffer both lateral and longitudinal translations, and work is ongoing to attempt to register adjacent images in the sequence. Currently this registration uses an approach based on the Scale Invariant Feature Transforms (SIFT) algorithm. Registration is a necessary stage in the construction of a 3D model of the subject’s cornea for use as a diagnostic aid. The algorithms, results, progress and suggestions for future work are presented in this chapter.
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Introduction

The Structure of the Cornea

The cornea is a collection of cells and proteins that constitute a very highly organized structure. It is the clear outer layer, covering the front of the eye. The cornea must remain transparent to transmit and refract light. The cornea does not contain blood vessels to feed or protect it from infection, However it receives its nourishment from tears and the aqueous humour (fluid filling the Anterior chamber which is the space between the lens and cornea). Figure 1 shows the anatomy of the eye, and inspecting it we can recognize that the anterior surface of the cornea, which is not uniformly curved (H.E. Kaufman 2000; MedicineNet 2010).

Figure 1.

The anatomy of the Eye (MedicineNet 2010)

The dimensions of the cornea are, on average, 12.6 mm in the horizontal direction median and 11.7 mm in the vertical median. Its thickness is not uniform, with the central cornea thinner than the peripheral cornea (520 µm =< thickness <= 650 µm) (H.E.Kaufman 2000). The cornea has a tear film on its front surface and three main layers separated by two thin membranes. The Epithelial layer is the outermost layer of the cornea and is separated by the Bowman’s membrane from the central Stroma layer, which in turn is separated by the Descemet’s membrane from the innermost Endothelium layer as shown in Figure 2. Approximate thicknesses of these layers in the normal cornea are given in Table 1 (H.E. Kaufman 2000; Reinstein, Archer et al. 2008).

Figure 2.

The corneal layers

Table 1.
The constituent layers of the cornea and their approximate thicknesses
orderLayer NameConstituentsThe Layer thickness
1Epithelium layerSquamous cell layerAbout 52 to 65 µm ≈ 10% of the cornea thickness
Wing cells
Basal cells
2Bowman’s LayerAbout 8 to 14 µm ≈ 2% of the cornea thickness
3Stroma LayerAbout 442 to 552 µm ≈ 85% of the cornea thickness
4Descemet's membraneAnterior banded layerAbout 10 to 12 µm≈ 2% of the cornea thickness
Non-banded layer
5Endothelium layerAbout 4 to 6About 4 - 6 µm ≈ 1% of the cornea thickness

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