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 point from the eye at which images are clear. The other limit of eye's accommodation is the near point.
For an unaccommodated emmetropic eye, the far point is at infinity, but for the sake of practicality, infinity is considered to be 6 m because the accommodation change from 6 m to infinity is negligible. See visual acuity or snellen chart for details about 6/6 (m) or 20/20 (ft) vision.
For an unaccommodated hypermetropic eye, incident light must be converging before entering the eye so as to focus on the retina. In this case (the hypermetropic eye) the focus point is behind the retina in virtual space, rather than on the retina screen.
Sometimes far point is given in diopters, which refers to the inverse of the distance stated above (see Simple myopia). For example, an individual that can see clearly out to 50 cm would have a far point of .
where FP is the distance to the patient's far point. P is negative, because a diverging lens is required.
This calculation can be improved by taking into account the distance between the spectacle lens and the human eye, which is usually about 1.5 cm:
- "Vision Correction | Physics". courses.lumenlearning.com. Retrieved 2019-12-05.