Fig. 4.10 Anterior segment ocular coherence tomography (AS-OCT, Visante OCT¨) image after penetrating keratoplasty showing a perfect interface between the cornea and the corneal graft (a). Spectral domain anterior segment ocular coherence tomography (SD-OCT, Spectralis¨) image of a Descemet stripping automated endothelial keratoplasty (DSAEK) (b)

Limitations

AS-OCT provides in vivo imaging of the entire cornea architecture. Developments of new systems based on different wavelengths and on better signal transduction and computerization have improved the spatial resolution as well as deep structure analyses. However, AS-OCT imaging is not able to reach the micrometric precision of IVCM yet. Even if it is a non-contact technique, it requires experienced operator to perform right acquisition and accurate image analysis. Reliability of the pachymetric measurements should be better assessed and improved in order to reach the gold standard that is still ultrasound measurement. Until today, AS-OCT offers axial imaging only, but new experimental devices should be able to perform plano imaging in the future.

Conclusion

IVCM and AS-OCT are noninvasive imaging techniques that provide highresolution images of the cornea, and numerous clinical applications have been demonstrated for both instruments. IVCM, by providing in vivo histological like images of the cornea, has been largely used in infectious keratitis, corneal dystrophies, and refractive surgery. AS-OCT by offering noninvasive cross sections of the anterior segment has demonstrated its usefulness in refractive and anterior segment surgery, as well as in corneal graft. Hence IVCM and AS-OCT offer complementary qualitative and quantitative data about the corneal structure, from micrometric cell imaging to 3D mapping of the corneal

architecture. The future of these techniques will be a better resolution but also the development of vital dyes, 3D and 2D image reconstruction softwares, and perhaps a combination of both techniques providing an in vivo noninvasive reconstruction at the cellular level of corneal and anterior segment structures.

Conflict of Interest The authors have no proprietary or commercial interest in any product or concept discussed in this article.

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Claus Cursiefen and Felix Bock

Core Messages

•The cornea uses redundant mechanisms to maintain its evolutionary highly conserved avascular state (“corneal angiogenic privilege”).

•Corneal angiogenesis is associated with the most common forms of corneal blindness.

•Corneal angiogenesis is primarily caused by inflammatory diseases of the cornea (e.g., keratitis), corneal hypoxia (contact lens wear), and limbal antiangiogenic barrier defects (most commonly aniridia, chemical burns).

•In corneal inflammation, (hem)angiogenesis (i.e., visible outgrowth of pathologic blood vessels into the cornea) is usually accompanied by lymphangiogenesis (i.e., invisible outgrowth of lymphatic vessels).

•Pathologic corneal lymphatic vessels are invisible at the slit-lamp, but can be visualized using specific immunohistochemical markers in explanted vascularized corneas as well as in vivo using HRT confocal microscopy with the cornea module.

•Preexisting blood and even more so lymphatic vessels are strong risk factors for immune rejections after keratoplasty. The same is true for neovascularization developing only after transplantation.

C. Cursiefen, M.D., FEBO (*) • F. Bock

Department of Ophthalmology, University of Cologne, Joseph-Stelzmann-Strasse 9, Köln D-50924, Germany e-mail: claus.cursiefen@uk-koeln.de