aging changes in crystalline lens
the lens grows throughout life. the majority of the increase in thickness occurs between ages 8 and 40, accompanied by an increase in surface curvatures, a forward movement of the center of the lens, and a decrease in anterior chamber depth. Other physical changes that accompany age were described in the section about presbyopia. Changes occur in lens physio;ogy as mature lens fiber lose all cellular organelles. A coincident decrease in the transport of ions, nutrients, and antioxidants may lead to damage contributing to cataract formation. With age there is am increase in fiber membrane permeability and the ionic pumps mat not be able to compensate, disrupting ion balance. Circulation within the lens changes and restriction of the flow of water and of glutathione occurs at the cortex/nucleus border. Significant changes in aquaporins occur, causing a disruption of water flow.
The amount of water soluble alpha crystallins decreases with age, and by age 45 there are no alpha crystallins evident in the lens nucleus. Since the alpha crystallins help to prevent other crystallins from forming aggregates, water insoluble aggregates increase with age. Some components of cytoskeleton disassemble. Levels of UVR filters in the lens decrease approximately 12% per decade, allowing increased UVR damage.
Clinical manifestations of aging are presbyopia and cataract formation. Both processes affect vision and are a significant concern to the patient and to the clinician, particularly because few preventive measures are available. Recommendations to patients should include the use of UVR-absorbing lenses when outdoor, the incidence of cataract is higher in those exposed to greater levels of sunlight.