Investigations on lens transparency and its disturbances by microdensitometric analyses of Scheimpflug photographs

During the aging process, the lens is subjected to changes of its pertinent properties which condition the transmission of light of different wavelengths. Between the second and the third decade, for instance, wavelengths below 400 nm are almost completely absorbed. The increase in lens thickness, effected by the appositional growth during life, might be considered responsible for this phenomenon, if the newly developing lens fibers in the outer periphery would synthesize proteins which, with respect to light transmission, differ from those formed during the embryonic phase. For such a phenomenon, however, no indication was found either by clinical observations or biochemical research. -Microdensitometric analysis of Scheimpflug-photographs of the anterior eye segment allows measurements of lens transparency in the single lens which directly depend on the respective wavelengths used in the photographic procedure. Investigations performed with this method on a normal age-grouped population, show that the changes in light transmission are most evident in two of the lens segments. The lens nucleus shows a continuous increase in light scatter during aging. Also the anterior cortex – particularly in the deeper layers – shows changes in light transmission. With advancing age (beginning between 30 and 40 years of age), increased lens fluorescence is found in the region of the deeper anterior cortex, which can be excited by UV wavelengths of 330–380 nm. This phenomenon is not found in the lens nucleus. The localization of the changes within the lens clearly shows that they are due to age-related modifications of the protein properties earlier designated as posttranslational or postsynthetic molecular modifications. A series of chemical reactions responsible for such modifications are also already known. Since the changes of light transmission in lens nucleus and anterior (deeper) lens cortex are of different quality, it may be supposed that different mechanisms are involved in the respective postsynthetic protein changes. With respect to the lens nucleus, it may be assumed that the formation of aggregates leading to high molecular weight proteins play a role, while in the lens cortex mostly oxidative changes are responsible.