TIME RESOLVED SPECTROSCOPIC STUDIES ON THE INTACT HUMAN LENS

Abstract— The human lens is continually under photooxidative stress from ambient radiation. In the young lens the major absorbing (between300–400 nm) species is the glucoside of 3-hydroxy kynurenine. Using time resolved fluorescence spectroscopy on both the isolated compound and the intact human lens, the first excited singlet state of this compound is shown to have fast (ps) decay processes. This would tend to minimize damage to lens constituents because there would be little time for energy transfer into more harmful channels. Thus, this compound appears to act as a protection for the retina. With aging, human lens proteins become yellow with absorptions out to 450 nm. Time resolved diffuse reflectance spectroscopic studies on intact older human lenses showed that excitation (355 nm) resulted in the formation of long lived (microseconds) transient species with an absorption maximum at ca 490 nm. Similar spectra were obtained from two model systems used to explain age related changes in human lens proteins.