distance


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distance

 [dis´tans]
the measure of space intervening between two objects or two points of reference.
interocclusal distance the distance between the occluding surfaces of the maxillary and mandibular teeth with the mandible in physiologic rest position.
interocular distance the distance between the eyes, usually used in reference to the interpupillary distance (the distance between the two pupils when the visual axes are parallel).

dis·tance

(dis'tăns),
The measure of space between two objects.
[L. distantia, fr. di-sto, to stand apart, be distant]

dis·tance

(dis'tăns)
The amount of space between two objects, points, or places.

distance

The amount of space between two points.
abathic distance See apparent frontoparallel plane.
distance between lenses (DBL) Horizontal distance between the nasal parts of the spectacle lenses in a frame, measured either along the datum line (datum system) or between the nasal peaks of the bevels of the two spectacle lenses (boxing system). See spectacle frame markings; boxing system.
distance between rims  (DBR) Horizontal distance between the bearing surfaces of a regular bridge of a spectacle frame, usually measured along the datum line, or at a specified distance below the crest of the bridge.
centration distance (CD) The specified horizontal distance between the right and left centration points of a pair of ophthalmic lenses. See near centration distance; centration point.
conjugate distance's An optical system will form an image of an object. As the path of light is reversible, the position of object and image are interchangeable. These pairs of object and image points are called conjugate points (or conjugate foci) and the distances of the object and the image from the optical surface are called the conjugate distances (Fig. D9). When an eye is accurately focused for an object, object and retina are conjugate. See emmetropia; Scheiner's experiment.
distance of distinct vision A conventional distance used in calculating the magnifying power of a loupe or microscope. It is usually taken as 25 cm (or 10 inches) from the eye. See apparent magnification.
focal distance See focal length.
hyperfocal distance That distance from a lens or optical system at which the depth of field, on the far side of an object in focus, extends to infinity. On the near side of the object the depth of field then extends to half that distance. This is a useful distance in photography as it represents the shortest distance on which to focus in order to obtain a reasonable image definition of an object at infinity and the longest total depth of field. This distance depends on the focal length and the diameter of the entrance pupil of the system as well as the amount of the allowable blur. See depth of field.
image distance The distance along the optical axis of a lens or optical system between the image plane and the secondary principal plane. If the system consists of a single thin lens, the image distance is measured from the optical surface and the reciprocal of this quantity is called the reduced image vergence or image vergence (in air). See principal plane; back vertex power.
interocular distance The distance between the centres of rotation of the eyes, i.e. the length of the base line.
interpupillary distance  (IPD, PD) The distance between the centres of the pupils of the eyes. It usually refers to the eyes fixating at distance, otherwise reference must be made to the fixation distance (e.g. near interpupillary distance). The average interpupillary distance for men is about 65 mm and for women about 62 mm (in Caucasians). Syn. pupillary distance. The interpupillary distance is often measured from the median plane to the centre of the pupil of each eye. This is referred to as the monocular pupillary distance (MPD): it is a useful measurement, especially in dispensing progressive lenses. The interpupillary distance for near vision can be calculated using the following formula:
near PD = ({d/d′}) distance PD
where d is the distance between the target plane and the spectacle plane and d′ the distance between the target plane and the midpoint between the centres of rotation of the eyes. See pupillometer; PD rule.
near centration distance  (NCD) The horizontal distance between the right and left centration points used for near vision.
object distance The distance along the optical axis of a lens or optical system between the object plane and the primary principal plane. If the system consists of a single thin lens, the object distance is measured from the optical surface and the reciprocal of this quantity is called the reduced object vergence or object vergence (in air). See front vertex power; vergence.
reading distance The normal distance at which people read. It is about 33-44 cm for men and 29-40 cm for women. It is a useful measurement in determining the reading addition.
vertex distance See vertex distance.
distance vision See distance vision.
working distance  (WD) 1. The distance at which a person reads or does close work. 2. In retinoscopy, the distance between the plane of the sighthole and that of the patient's spectacles. 3. In microscopy, the distance between an object and the front surface of the objective.
Fig. D9 Conjugate distances k and k′ and conjugate points M R and M′ in the eye (M R , far point of the eye; M′, foveola)enlarge picture
Fig. D9 Conjugate distances k and k′ and conjugate points MR and M′ in the eye (MR, far point of the eye; M′, foveola)

Table D5 Calculated near PD (in mm) as a function of distance PD for three reading distances (target plane to spectacle plane). The distance between the spectacle plane and the midpoint of the base line is assumed to be 27 mm (vertex distance 12 mm)
distance PD56586062646668707274
near PD for 45 cm52.854.756.658.560.462.364.266.067.969.8
difference3.23.3 3.4 3.5 3.6 3.7 3.8 4.0 4.1 4.2
near PD for 40 cm52.554.356.258.159.961.863.765.667.469.3
difference3.53.7 3.8 3.9 4.1 4.2 4.3 4.4 4.6 4.7
near PD for 35 cm52.053.855.757.659.461.363.165.066.868.7
difference4.04.2 4.3 4.4 4.6 4.7 4.9 5.0 5.2 5.3

dis·tance

(dis'tăns)
Measure of space between two objects.
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