In vivo confocal microscopy for evaluation of wound healing following corneal refractive surgery
Section snippets
History of in vivo imaging of the cornea
The development of the slit lamp by Gullstrand (Duke-Elder, 1962) for biomicroscopy of cornea and deeper ocular structures was a major benchmark (Cavanagh et al (1990), Cavanagh et al (1993), Cavanagh et al (1995), Cavanagh et al (2000); Masters and Farmer, 1993; Masters et al. (2001), Masters et al. (2002); Petroll et al., 1998) of corneal imaging. The microscope uses a narrow slit to remove part of the scattered light from adjacent tissue structures enabling a degree of optical sectioning,
Basic parameters of the cornea
Tear film: Prydal and Campbell (1992) have used TSCM to measure the thickness of tear film. However, the applanating objective and use of Goniosol® gel may disturb estimation of tear characteristics.
Epithelium: Irrespective of the type of the microscope, both superficial (Fig. 2A) and basal epithelial cells are easily visualised (Fig. 2B). The impact of limbal stem cell deficiency on corneal healing has also been assessed by IVCM (Cho et al., 1998). Bowman's layer appears as a cell free area,
Radial keratectomy (RK)
RK was the first procedure widely used to alter corneal refractive power. It is based on incision wounds (Jester et al., 1992b), the histology of which has been reviewed in this journal (Jester et al., 1999b). Briefly, an incision wound is first filled by epithelial cells sliding into the wound cleft. Subsequently, these cells form an epithelial plug (at 7 days) that is later replaced by activated keratocytes adapting myofibroblast-like phenotype (at 14 days). These cells accomplish
Nerve regeneration after refractive surgery
Both PRK (Campos et al., 1992; Ishikawa et al., 1994; Trabucchi et al., 1994; Kohlhaas et al., 1995; Perez-Santonja et al., 1999; Benitez-del-Castillo et al., 2001) and LASIK (Kanellopoulos et al., 1997; Chuck et al., 2000, Perez-Santonja et al., 1999; Matsui et al., 2001; Linna et al., 2000a; Ang et al., 2001) severe corneal nerves and lead to a loss of corneal sensitivity.
PRK ablates Bowman's layer and the subepithelial nerve plexus. The Bowman's layer shows only minimal if any regeneration
Interphase debris
Vesaluoma et al. (2000a) showed that there are about 600 (mean) particles per square milllimeter 3 days after LASIK. The particles (Fig. 16A) presumably include cells, cell fragments (apoptotic bodies), debris, metal particles, and salt presipitates from tear film. One month post-operatively the particle count was lower. Improved cleaning procedures adopted after that study seem to have decreased the particle counts. The significance of interphase particles to LASIK complications, such as DLK
Other possibilities in corneal imaging
Means of imaging corneal or other tissues in the eye are being constantly developed. Optical Coherence Tomography (OCT; Humphrey-Zeiss Medical Systems) developed for imaging of retina and optic nerve can also be used for imaging of the cornea and estimation of central corneal thickness (Bechmann et al., 2001; Muscat et al., 2002; Wirbelauer et al., 2002; Neubauer et al., 2002). Nidek EAS-100 anterior segment analysis system also enables imaging of the whole anterior segment including the
Acknowledgements
Acknowledge is extended to the collaborators and mentors, who have instructed either of the writers into the field of confocal microscopy or corneal refractive surgery or participated in the creation of the results presented. Starting from the beginning, discussions with Stephen Trokel, inventor of PRK and Steven E Wilson, a good friend and prominent scientist in the field of corneal wound healing are to be acknowledged. The authors are also grateful for Professor Wilson for reading and
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