Mouse lens stiffness measurements

Presbyopia is a gradual loss of accommodation with age. Various studies have shown that an age-related increase in lens stiffness may be one factor involved. Lens stiffness has previously been measured using lens spinning experiments, resistance to conical probe penetration and dynamic mechanical analysis. In the current study, two different techniques have been used to evaluate the stiffness of isolated mouse lenses. In the first method, compressive forces were applied to mouse lenses using microscope cover-slips to exert incremental forces on the lens. Lens images were captured for analysis of change in diameter. In the second method, a fully automated squeezer system with an actuator, electronic scale and a CCD camera was used to apply incremental compressive forces to the lenses. The actuator exerted forces comparable to those exerted by cover-slips. Force and actuator displacement data together with images of the lenses as they were compressed were captured. Images were analyzed for change in lens diameter on application of force and also with actuator displacement. Lenses from 19 young male mice (4-weeks old) and 28 male retired breeders (7-9 months old) were tested. Lenses were used immediately after sacrificing the mice and extracting the lenses. The lenses from the older male mice were stiffer compared to the lenses from the younger male mice. This was determined by comparing the average change in lens diameter at various force values used. The two methods provide a good indication of the stiffness properties of mouse lenses.