Variation of the concentration of sulfhydryl along the visual axis of aging lenses by laser Raman optical dissection technique

Abstract

Laser Raman spectroscopy is a powerful, non-invasive analytical technique for studies of constituents in the intact lens. It was employed here to measure the variation of sulfhydryl levels (protein -SH plus glutathione -SH) along the visual axis (VA) of the lenses of different ages. The VA length of each rat and mouse lens was measured using a translation stage micrometer and the laser scattering. The rat VA length varied from 2·85 mm (26 days) to 4·32 mm (16 months). Spectra were obtained for 20 increments along the VA. The results are presented as VA profiles. The salient features in the series of curves are two maxima in the cortex (one anterior, one posterior) and a central minimum. The youngest rat lens (maintained at 37°C to avoid cold cataract) showed a bell-shaped curve. All curves were nearly symmetric for the rat, the minima slightly off center for the mouse. The two maxima of the second youngest rat lens were separated by a distance of 1·55 mm which increased to 2·95 mm in the oldest lens. In a 7 1 2 month lens a 0·78 mm segment of the VA center contained too little sulfhydryl to be detected by this technique. This segment increased to 1·44 mm in the oldest lens. The apparent rate of decrease in SH, being quite pronounced in the nucleus, is different at other points along the VA. A plot of sulfhydryl level vs. age for several points at distance r from the center (VA midpoint) along the VA indicates a steady decrease in SH levels with age for r < 1·2 mm. For larger r, there is actually an increase in SH. These results are interpreted in terms of 2SH→S-S conversion, changing rates of synthesis of the different crystallins and of glutathione synthesis along the VA.