Matsuura T, Gorti S, Tanaka T, Hara Y, Saishin M
Department of Physics, Massachusetts Institute of Technology, Cambridge 02139, USA.
Eur Biophys J. 1999;28(5):357-68. doi: 10.1007/s002490050220.
From observations of the dynamics of light scattered by the cornea, intensity autocorrelation functions that revealed two independent diffusion coefficients, D (fast) = 2.4 +/- 0.2 x 10(-7) cm2/s and D (slow) = 9.4 +/- 1.3 x 10(-9) cm2/s, were obtained. The diffusion coefficients were found to be statistically independent of the position and depth on the lateral surface of the cornea from which the scattered light was sampled. The slow diffusion coefficients obtained from light sampled from within cross-sections of the cornea were, however, measurably different. Diffusion coefficients obtained independently from observations of the kinetics of corneal swelling for comparison were found to be several orders of magnitude greater than those obtained from light scattering. The large disparity in the diffusion coefficients obtained from the two independent methods invoked the possibility that the lamellar layers within the cornea behave as individual gel sheets. Irrespective of this additional hypothesis, divergent behavior in the measured total scattered light intensities and diffusion coefficients upon varying external conditions, such as temperature or pressure (stretching), was observed. Namely, a slowing down of the dynamic modes accompanied by increased "static" scattered light intensities was observed. Although the slowing down of the dynamic modes is possibly indicative of the reduced affinity of protein binding to the gel matrix that "softens" the gel, the divergent behavior in the scattered light intensities and diffusion coefficients is, however, more characteristic of a phase transition. In addition, the divergent behavior in the scattered light intensities and diffusion coefficients was reversible up to a critical temperature (approximately 50 degrees C) or stretching (approximately 16%).
