A decrease in the permeability of aquaporin zero as a possible cause for presbyopia.

The crystalline lens appears to be a simple organ with the sole role of focusing light upon the retina. However, numerous studies have underscored its dynamic nature with a host of compartmentalized physiological processes. As the individual ages, the normal lens develops two inescapable processes, presbyopia and cataracts. Yet, to date, there is no uniform explanation for presbyopia and many factors have been proposed as contributors including continuous enlargement of the lens, loss of power of the ciliary muscle and hardening of the lens fibers. Proposed explanations are incomplete and need experimental confirmation. This paper analyzes the possible causes for presbyopia and proposes a new one for it: a decrease in the permeability of aquaporin zero (AQP-0) also known as major intrinsic protein (MIP). Based on original findings of our laboratory, this paper proposes that a fluid flow exists inside the avascular lens. This fluid enters and leaves the lens during the accommodation process. We believe that for this to occur the lens utilizes the permeability of aquaporin zero which is abundant in the membrane of the fiber cells. Volume change due to fluid traversing the surface of the lens occurs during accommodation. We present the hypothesis that increasing the permeability of AQP-0 would facilitate accommodation. Therefore, defects in AQP-0 permeability may be a cause for presbyopia. We would also like to propose that it is possible to visualize and measure the fluid volume lost during un-accommodation and determine if the fluid is lost across the anterior, posterior or both surfaces. An age-related loss in lens water permeability could reduce fluid fluxes during the shape changes of accommodation potentially contributing to presbyopia.

Volume change of the ocular lens during accommodation.

During accommodation, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.

[The aging heart and its pathology. An epidemiological study of 229 cases based on a clinical and radiological classification]. / Il cuore senile e la sua patologia. Studio epidemiologico di 229 osservazioni, in base ad una classificazione clinica e radiologica.

The paper studies epidemiological distribution of the aging heart and its pathology in a sample of 229 subjects (101 male and 128 female) on the basis of a clinical and radiological classification into cardiological phenotypes. This study involved the use of mathematical statistical procedures following a standard method using SIR database (Scientific Information Retrieval) software implemented on the CDC Cyber 170/730 mainframe in the Trieste University Computing Center that is connected with the Chair of Geriatric Pathology. Using this software it was possible to assess the epidemiological significance of the usual clinical parameters, and show that the most representative cardiopathy is the 3rd type, i.e. the hypertrophic-ischemic cardiopathy belonging to the large aortic heart. Its natural pathogenesis is independent of risk factors and relates to the aging of muscular and connective tissues in which the coronary circulation is involved in the deterioration of the cardiovascular system and is therefore different from the primary ischemias of adults.