How is the refraction test used to diagnose presbyopia?

Age related: Presbyopia is tested for after age 40 or so. It is due to the inevitable hardening of the lens which becomes visually evident between ages 40-55 when the lens no longer is flexible. It is tested in that age group by near vision apparatus in your ophthalmologists' office however there are formulas which can be used which are reliable for power and commonly applied without testing after refraction.