Presbyopia
The age-related loss of accommodation power in the human eye caused by reduced elasticity of the crystalline lens.
Governing formula
Near Point > 25 cm (increases with age)
SI unit
Diopters (D)
In depth
As the eye lens hardens with age, ciliary muscles cannot increase lens curvature sufficiently for close vision, moving near point beyond arm's length.
Examples in the real world
Older adults holding reading material far away or using convex reading glasses ($+1.5 D$ to $+2.5 D$).