Near point


In visual perception, the near point is the closest point at which an object can be placed and still form a focused image on the retina, within the eye's accommodation range. The other limit to the eye's accommodation range is the far point.
A normal eye is considered to have a near point at 25 cm. A person with hyperopia or presbyopia would have a near point further than 25 cm away.
Sometimes, near point is also given in diopters, which refers to the inverse of the distance stated above

Vision correction

A person with hyperopia has, and hence is unable to bring an object 25 cm away into sharp focus. A corrective lens can be used to correct hyperopia by imaging an object at distance onto a virtual image at the patient's near point. From the thin lens formula, the required lens will have optical power given by
The calculation can be further improved by taking into account the distance between the spectacle lens and the human eye, which is usually about 1.5 cm:
For example, if a person has, then the optical power needed is where one diopter is the reciprocal of one meter.