Noun
1. Inability of the eye, due to ageing, to focus on nearby objects
Presbyopia (Greek word “presbys” (πρέσβυς), meaning “old man” or “elder”, with Latin root “-opia”, meaning “eye”) 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.
Similar to grey hair and wrinkles, presbyopia is a symptom caused by the natural course of aging; the direct translation of the condition’s name is “elder eye”. The first symptoms are usually first noticed between the ages of 40-50. The ability to focus on near objects declines throughout life.
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 extreme 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 smaller diameter. As with any lens, increasing the focal ratio of the lens increases depth of field by reducing the level of blur of out-of-focus objects (compare the effect of aperture on depth of field in photography).
Read more about presbyopia on Wikipedia