Answer
Presbyopia is an age-related change in the lens that results in a decrease in its elasticity. As a consequence, the degree of canvexity achievable is less, and the power of convergence of the lens is decreased. In this condition, the accomodation deficit results in a decline in the ability of the sufferer to focus on near objects. As in farsightedness, print held at normal distance comes to focus behind the retina. Therefore, the affected person has to compensate by holding the book or paper farther than normal reading distance to get the print in focus. The increase in distance necessary at age 45 may be about eight inches, but the distance gets greater, absent artificial correction of the vision.
Work Step by Step
In presbyopia, there is a problem with near vision. As a result print held at normal reading distance is out of focus, and fuzzy. This is the case because the lens has lessened power of convergence secondary to decrease convexity. As a consequence, light from near objects focus behind the retina. This problem can easily be corrected with artificial lenses. The problem is similar to farsightedness but in presbyopia, the cause is loss of elasticity and convexity of the lens, and not an inherited abnormally short eyeball.
