Accommodation is the process of changing the shape of the eye’s internal lens to focus light coming from different distances. This is accomplished by altering the tension in the muscle that surrounds the lens to regulate its shape and thickness. It’s what an engineer calls a closed loop feedback system. The image formed on the retina is digitized, sent to the brain, evaluated by the brain for clarity, and adjusted by feedback impulses to the muscle. It’s constantly changing and adjusting to maximize clarity.
The flexibility of the crystalline lens decreases with age, making accomodation more difficult, and creating blur with near vision in people over 40. People often imagine that decreases in clarity and facility of near vision are caused by the muscle becoming weaker. Actually, the opposite happens. By working harder to change the shape of the lens, the ciliary muscle actually increases its mass and effectiveness. It cannot increase it enough to make a difference, however, and as we continue to age, the ongoing loss of flexibility in the lens make near vision impractical without stronger lenses.
There is no truth to the idea that wearing glasses makes your eyes weaker, so you shouldn’t avoid wearing glasses if you need them. The changes that create the problem are all part of the wrinkles and gray hair process. It’s an inescapable fact that age related changes decrease the efficiency of most of our physical aspects. As far as vision goes, we have the means to make it comfortable again with glasses or contact lenses.