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Mapping Collagen Organization in the Human Cornea
Author Response: Mapping Collagen Organization in the Human Cornea
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Norman S. Levy
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afn22025{at}afn.org Norman S. Levy
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The observations of Boote et al.1 on the distinct arrangement of the collagen fibrils in paired corneas suggested a possible explanation for a recent observation using the GDx VCC Nerve Fiber Analyzer.2 We measured the reproducibility of scanning laser polarimetry of corneas in paired eyes from the same individuals, using the GDx Nerve Fiber Analyzer (VCC). There were 33 subjects who participated in this study [Age Range: 18-22 years]. The optical pathway for determining the VCC included the central cornea, pupil, lens, vitreous and the macula. Since the central macula contains few polarizing ganglion cell axons and the fibers of Henle (which also polarize light) are symmetrically arranged, the measured polarization of the reflected beam is principally due to the cornea. In our study, there was a difference in retardation between right and left eyes of 5.26 ± 9 nm, p = .002. We concluded that this difference may reflect an equipment induced measurement artifact and/or an anatomic asymmetry between the paired eyes of the subjects studied. The demonstration by Boote et al.1 of distinct arrangements of the collagen fibrils in paired right and left corneas suggests one possible explanation for the asymmetry in corneal polarization measured by the GDx-VCC Nerve Fiber Analyzer.2 Norman S. Levy Florida Ophthalmic Institute, Gainesville, FL References 1. Boote C, Hayes S, Abahussin M, Meek KM. Mapping collagen organization in the human cornea: left and right eyes are structurally distinct. Invest Ophthalmol Vis Sci. 2006;47:901-908. |
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Keith M. Meek
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meekkm{at}cf.ac.uk Keith M. Meek
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Drs. Levy and Schachar draw attention to the intriguing possibility that our report of differences in the arrangement of lamellae between left and right corneas1 may explain their own observation of a difference in retardation between right and left human eyes. We believe that the mirror symmetry in the preferred orientations of lamellae may explain the well documented enantiomorphism in the topography of left and right corneas2 as well as some of the polarisation and birefringence properties of the cornea. In this respect it is interesting, for example, that there is a similar mirror symmetry in corneal birefringence.3 However, it should be borne in mind that the rhombic pattern that we describe relates to lamellae in the peripheral cornea, whereas the data from Levy and Schachar4 were obtained from the central cornea. Only at larger pupil diameters would the asymmetry between left and right eyes we have described be evident along the optical path. A more detailed investigation is necessary to see if this left/right symmetry, evident in the limbus and the peripheral cornea, extends to the lamellae in the central cornea. Keith M. Meek and Craig Boote School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom References 1. Boote C, Hayes S, Abahussin M, Meek KM. Mapping collagen organization in the human cornea: lefta nd right eyes are structurally distinct. Invest Ophthalmol Vis Sci. 2006;47:901-908. |
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