The classic example of your child putting a picture in front of your nose and you grabbing the photo to place it at your arm's length and maybe toward a window, illustrates the phenomenon quite well. The condition is called presbyopia and we will ALL get it, sooner or later. Actually, presbyopia probably begins around age fifteen. The focusing ability of children's eyes is tremendous but it peaks during the mid-teens and actually shows a slight loss by age 20.
Many people ask if exercising their eye muscles can help prevent the condition.
If presbyopia was a muscle problem, I would have to answer, yes. Besides, the muscles that turn and focus the eyes are ten times stronger than they ever need to be. The lens of the eye is actually rather unique. We take it's function for granted for many years, looking at objects all around us and at different distances away from us, not even aware of the millions of little focusing adjustments necessary to see clearly all day. All those adjustments are automatic and take place at a blistering pace.