According to the information provided, the crystalline lens is harder as a result of what?

The crystalline lens becomes harder primarily due to an increase in cell layers. As a person ages, the lens continues to add new layers of cells, which contribute to its overall density and firmness. This process is a natural part of the lens's development and aging. While these extra layers can enhance the lens's refractive power, they also make it less flexible, which is why older individuals often experience difficulties with near vision, known as presbyopia.

Other factors, though significant to the overall health and function of the lens, have different implications for lens hardness. Loss of elasticity contributes to the difficulty in focusing but does not directly explain the increase in hardness. Increased calcium deposits, although they may occur, typically relate more to cataract formation than to the general hardness of the lens. Similarly, fluid accumulation can affect lens clarity but does not specifically refer to the development of hardness in the context of aging. Thus, the increase in cell layers is the primary factor contributing to the hardness of the crystalline lens.