Presbyopia is a physiological condition of the visual system, not belonging to the refractive defects. It is typically linked to a loss of efficiency of the accommodative. In particular, there is a progressive loss of elasticity of the crystalline lens.
Occurs on average around 40 years old and according to several studies is lower in people living in low latitudes. 
It presents with blurred vision and blurred vision, improved by increasing the distance of focus or increasing the illumination of the object observed. It has a secondary effect in the almost simultaneous farsighted difficulties for accommodation for far longer than at least +1.50 diopters. 
Chart of the decrease in accommodative amplitude in relation to age.
The correction is done with lenses positive or less negative in cases of myopic presbyopic. Other solutions compensatory are represented by the use of contact lenses, generally of type multifocal. Refractive surgery in this case can not be helpful since it is by far the power which is to change in case of intervention. They are, however, ongoing studies and tests of plant crystalline progressive.