Presbyopia or Dysfunctional Lens Syndrome
Presbyopia, is not truly a refractive error, but is the natural process of the eye losing the ability to accommodate or change the shape of the natural crystalline lens inside the eye to see comfortably at near.
Usually over the age of 40 this ability to see near objects clear becomes less. The best information we have today regarding the gradual loss of accommodation places blame on the lens itself.
Unlike the rest of the body, which stops growing by the age of twenty, the lens of the eye continues to grow throughout life. As the lens ages and grows, it becomes harder in consistency and, therefore, resistant to changes in shape.
The result is a gradual reduction in accommodation, and a more dependence on reading glasses.