Submicroscopic structure of rabbit cornea studied by polarization optics and thermoelasticity.

The present investigation was undertak en to obtain some knowledge about the submicroscopic structure of the cornea based on thermoelastic properties and polarization characteristics. Previous workers b have reported that the cornea exhibits a birefringence of uniaxial type. But as their observations were made in parallel polarized light only, it is desirable to make conoscopic observation as well in convergent polarized light. The general appearance of the cornea between crossed nicols is such that the birefringent elements are predominantly arranged in a radial manner, although no anatomical evidence of such a radial arrangement has been reported. In the present investigation, isolated whole corneas were examined from the direction normal to the surface. In parallel polarized light, the corneal fibers were ascertained to be arranged radially. In convergent polarized light, a biaxial interference figure was obtained in place of a uniaxial one. The cornea consists chiefly of collagen, which is composed, like that elsewhere in the body, of long chain molecules, some of them aggregated together to form micelles (5 per cent. of the corneal substances, Naylor 1953 (3) ). Consequently, birefringence may be considered as due to only a small proportion of the corneal substances. As the second approach to the problem, the fine structure of the cornea was analysed from the point of view of its mechanical behavior. The analysis of thermoelastic properties has, in particular, been quite successfuLin a number of cases.c In the present work, the last method was applied to the study of the cornea, and the molecular interpretation led to the conclusion that the cornea is composed of many layers of two-dimensional networks of long chain molecules. Further, it was shown that the temporary impairment of transparency due to an applied pressure to the cornea may be considered as a sort of crystallization.