Common vision problems
Presbyopia
Presbyopia (Greek word "presbys" (πρέσβυς), meaning "old person") describes the condition where the eye exhibits a progressively diminished ability to focus on near objects with age.
Presbyopia's exact mechanisms are not known with certainty, however, the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens's curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated as its cause.
Presbyopia is a condition that causes the natural lens of the eye to become less flexible, and reduces the eye's ability to switch between one focal point and another. This becomes more noticeable with age, typically affecting vision by middle age.
The first symptoms most people notice are, difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances. Many advanced presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.
Presbyopia, like other focus defects, becomes much less noticeable in bright sunlight. This is a result of the iris closing to a pinhole, so that depth of focus, regardless of actual ability to focus, is greatly enhanced, as in a pinhole camera which produces images without any lens at all.
A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupils. In particular, farmers and housewives seek correction later, whereas service workers and construction workers seek eyesight correction earlier.
By age 50, almost everyone has issues with near vision. Imperfections in the focusing power of the eye are called refractive errors. There are three primary types of refractive errors: myopia, hyperopia and astigmatism.