When a person is about 40-50 years old, the ability to accommodate has been lost at all. From then on, the “add” determines your point of best focus and having the focal length of a +2.50D lens means that the person can see clearly at 2/5 meter.
Moreover, in a positive diopter measurement, use 1 as the numerator to find the distance in meters then take the value of 2.5 and make it the denominator. Then, you will have1/2.5, which is equal to 2/5 of a meter.