A near sighted eye usually has an eyeball that is too long from front to back. This extra length makes light rays from distant objects meet before they reach the retina. By the time the light rays reached the retina, they have begun to spread again and are no longer in focus. A farsighted eye usually is too short from front to back. Because the eye is too short, light rays tend to strike the retina before they have come all the way together. The lens has to compensate for the shortness of the eye by becoming thicker and more contracted so it can bend light rays farther than is necessary in a normal eye. The lens of the far sighted eye can usually achieve the extra thickness necessary to bend the parallel rays from distant objects, but bending the spreading rays. From nearby, objects sometimes requires more contraction than is possible. In almost all people, the lens of the eye becomes stiffer and less able to contract and thicken as they age, which leads to far sightedness. For this reason, most middle-aged and elderly people need glasses for reading, even if they didn't need glasses when they were younger.