Brillouin scattering, density and elastic properties of the lens and cornea of the eye.

Brillouin spectra of biological systems may ultimately be related to their intrinsic molecular properties. In some instances the optical properties may be associated with the elastic ones and ultimately with the force constants of the molecules involved. In the present work we have used a triple-pass Fabry-Perot interferometer to measure Brillouin light scattering spectra for refractive tissues of the eye, including cornea, capsule and lens. Combined with corresponding measurements of density, estimates of the real and imaginary parts M' and M'' of the longitudinal bulk modulus have been made for the first time. Measurements have extended over four classes of vertebrate: Mammalia, Aves, Pisces and Amphibia; only small differences have been found between the various samples of cornea, whereas marked differences occur between the different lenses. Hence this account concentrates largely on the latter. The implications of this work lie not so much at the ophthalmological level as at the macromolecular and offer, in conjunction with other scattering techniques, opportunities for probing the lens and its proteins topographically as a function of growth.