visual perception Visual perception is the ability to detect light and use it to form an image of the surrounding Biophysical environment, environment. Photodetection without image formation is classified as ''light sensing''. In most vertebrates, visual percept ...

, the near point is the closest point at which an object can be placed and still form a focused image on the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

, within the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

's accommodation range. The other limit to the eye's accommodation range is the

far point In visual perception, the far point is the farthest point at which an object can be placed (along the optical axis of the eye) for its image to be focused on the retina within the eye's accommodation. It is sometimes described as the farthest ...

. A normal eye is considered to have a near point at about for a thirty year old. The near point is highly age dependent (see accommodation). A person with

hyperopia Far-sightedness, also known as long-sightedness, hypermetropia, and hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blur is due to incoming light being focused behind, instead o ...

presbyopia Presbyopia is a physiological insufficiency of optical Accommodation (vertebrate eye), accommodation associated with the aging of the human eye, eye; it results in progressively worsening ability to focus clearly on close objects. Also known as ...

would have a near point that is farther than normal. Sometimes, near point is given in diopters (see ), which refers to the inverse of the distance. For example a normal eye would have a near point of

\frac = 9\ \text

Vision correction

A person with hyperopia has a near point that is further away than the typical near point for someone their age, and hence the person is unable to bring an object at the typical near point distance into sharp focus. A

corrective lens A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are w ...

can be used to correct hyperopia by imaging an object at the typical near point distance onto a

virtual image In optics, the ''image'' of an object is defined as the collection of Focus (optics), focus points of Ray (optics), light rays coming from the object. A ''real image'' is the collection of focus points made by Vergence (optics), converging ray ...

at the patient's actual near point, at distance . From the thin lens formula, the required lens will have

optical power In optics, optical power (also referred to as dioptric power, refractive power, focal power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the ...

given by

P \approx \frac-\frac.

The calculation can be further improved by taking into account the distance between the

spectacle lens A corrective lens is a Lens, transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are wor ...

and the human eye, which is usually about 1.5 cm:

P = \frac-\frac.

For example, if a person has and the typical near point distance at their age is , then the optical power needed is where one diopter is the reciprocal of one meter.

References

Ophthalmology {{eye-stub