[Dielectric behavior of rat lens and changes due to cold cataract]

To correlate the formation of cold cataract with changes in the passive electrical properties of the lens, we measured impedances of isolated rat lenses in the frequency range from 100 Hz to 500 MHz. Temperature-dependent, reversible changes were confirmed in the dielectric behavior as well as in the histological characteristics. The impedance of lenses showed two separate peaks (i.e. P1 and P2) when expressed in terms of loss tangent. At a low temperature of 4 degrees C, cytoplasmic "aggregates" characteristic of the cold cataract were formed inside the fiber cells of young rats with concomitant decreases in P2 (the peak value at higher frequencies), whereas no remarkable changes occurred in the control group. These results indicate that the lowering of P2 may reflect functional changes in the lens fiber membrane, an augmented heterogeneity in cytoplasm and/or decreases of protein-bound water. We conclude that the P2 is a useful dielectric index for the assessment of the nuclear opacity. This is the first report on the application of dielectric techniques to lenses with nuclear cataract. We suggest that dielectric spectroscopy may be applicable to a quantitative evaluation of cataract, not only of the cortical type but also of the nuclear type.