Peter C. Magnante

Quantitative detection of the molecular changes associated with early cataractogenesis in the living human lens using quasielastic light scattering

We have used quasielastic light scattering to detect and quantitatively characterize the molecular changes associated with the early stages of cataractogenesis in the living human lens. The autocorrelation function of the fluctuations in the light scattered by the lens shows the presence of two major species responsible for the scattering. The first, fast diffusing species (f), has a diffusivity of approximately 3 x 10(-7) cm2/sec and corresponds to the alpha crystallin proteins. The second, slow diffusing species (s), has a diffusivity of approximately 10(-9) cm2/sec and corresponds to the diffusivity of a large aggregate. The intensity of light If and Is scattered into the collection optics by each of these species was also measured. We studied a group of 49 individuals ranging in age from 21 years to 82 years. In this group 40 presented with preoperative cataract development. In this patient population we found that regardless of age, or position in the lens that a plot of Itot = If+Is versus Is could be well fitted by a straight line with a slope less than unity and a positive intercept Ifo. It has been possible to explain this finding using a two state model for the molecular changes associated with early cataractogenesis. In this model the proteins in the slow diffusing species are aggregates each containing a definite number of rapidly diffusing proteins. The early development of cataract is represented by the redistribution of protein between the unaggregated form (f) and the aggregated form (s). The prediction for the relationship between Itot and Is based on this two state model is in very good agreement with our experimental data. Indeed the measured position of the point (Itot, Is) along this line provides a sensitive, and quantitative measure of the degree of cataract development at any selected location in the lens.

In vivo measurement of the aging rabbit lens using quasielastic light scattering

We have been able to analyze the autocorrelation function of the light scattered from the rabbit lens in vivo in terms of a two component, exponential fit. We have measured the intensity and the decay rate associated with each of these two components as a function of age and position in the lens. As far as is possible we have interpreted these results in terms of molecular changes in the state of association of the protein constituents in the aging rabbit lens. These studies suggest that the method of quasielastic light scattering spectroscopy can provide a useful probe of the protein modifications that occur in both normal and cataractous human lenses.

In Vivo Uses of Quasi-Elastic Light Scattering Spectroscopy as a Molecular Probe in the Anterior Segment of the Eye

Historically, light scattering has been used to study the size and shape of macromolecules in solution as well as the properties of a wide range of condensed materials, such as colloidal suspensions, gels, and solid polymers. When light interacts with matter, the energy of the interacting light photons can change. Photon energy can be gained from or lost to the translational, rotational, vibrational, and electronic degrees of freedom of the molecule. The resulting scattered light therefore undergoes frequency shifts. The frequency shifts, together with the angular distribution, polarization, and intensity of the scattered light depend on the size, shape, and molecular interactions in the scattering material. It is theoretically possible, by measuring these light scattering characteristics, to obtain information about the structure and molecular dynamics of the scatterers.

In Vivo Measurements On Human Lens Using Quasielastic Light Scattering

Quasi-elastic light scattering is a useful method to determine the size distribution of sub-micron particles in fluids. We have applied this technique to measure in vivo changes in the association of human lens protein constituents that occur with aging and cataractogenesis. The autocorrelation function of the scattered light has been analyzed by a two component exponential where each component is characterized by an intensity and decay rate. Each pair of parameters is associated with one of two major protein components in the lens. These parameters have been determined as a function of age and position within normal, clear lenses. In cataractous lenses the intensity and decay rate parameters show anomalous behavior, when compared to normal lenses, even in clear regions of the lens which are some distance from the cataract. Our results seem to be consistent with the model of progressive aggregation of the lens proteins as detected in vitro by other biochemical methods. Our studies suggest that quasi-elastic light scattering spectroscopy is a useful probe of the protein modifications that occur both in normal and cataractogenic human lenses.