The work Presbyopia has it beginnings in the Greek language (πρεσβύτερος), meaning "elder". It is the eye's diminished ability to focus that occurs with aging. There are two theories as to its cause. The most common is that it arises from the loss of elasticity of the crystalline lens. The second theory is that changes in the lens's curvature from continual growth and weakness in the muscles that bend and straighten the lens causes loss of focus. Presbyopia is not a disease. It is a condition that affects people as they age. Generally people begin to notice this in the 40s. In fact the ability to focus declines throughout life, from an accommodation of about 20 dioptres (ability to focus at 50 mm away) in a young person to 10 dioptres at 25 and levelling off at 0.5 to 1 dioptre at age 60 (ability to focus down to 1 -2 metres only). For those with good distance vision, it may start with difficulty reading fine print, particularly if the lighting is poor, or with eyestrain when reading for long periods. Many advanced presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.
In bright sunlight, Presbyopia is much less noticeable. This is cuased by the iris closing to a pin hole which improves focus. This works in the same way as a pinhole camera which produces images without any lens at all.
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