The present invention relates to a method and a device for measuring a pupil distance including an interpupillary distance and a monocular pupil distance between a center line of a bridge of a nose of a subject and a pupil of each of left and right eyes of the subject.
Eyeglasses and binocular magnifying glasses are configured such that optical axes of left and right lenses (left and right optical systems) for left and right eyes are located at pupil positions of a wearer. To determine a distance between left and right optical axes of the left and right lenses (or left and right optical system), it is required to measure an interpupillary distance of the user. The interpupillary distance is a distance between centers of pupils of left and right eyes measured when a person observes a distant, forward object. The interpupillary distance is equal to a distance between centers of rotation of left and right eyes.
In general, a PD meter or a measurement device for measuring an interpupillary distance provided in a refractive power measurement device (which is used to measure power objectively) is used to measure the interpupillary distance. However, such conventional devices for measuring the interpupillary distance (e.g., the PD meter and the measuring device provided in the refractive power measurement device) have complicated structures and are expensive.
Japanese Patent Provisional Publication No. HEI 6-205740 discloses a measurement device for measuring an interpupillary distance. The measurement device disclosed in this publication includes two plates slidably attached to each other. Each plate has a measurement window in which a center line is formed perpendicularly to a sliding direction. One of the plates has scale marks and the other of the plates has a pointer.
A subject (a person to be tested) holds the measurement device and adjusts the measurement device so that the center lines in the measurement windows coincide with centers of pupils of the subject, respectively, while observing an object through the measurement windows. By reading the scale marks pointed by the pointer, the interpupillary distance of the subject is obtained.
One of problems of the measurement device disclosed in the above mentioned publication is that the subject is required to conduct the adjustment of the measurement device while holding the measurement device. In such a case, the measurement device tends to become unstable, by which the measurement of the interpuillary distance becomes difficult.
A digital PD meter of a product number NO.455 is available from SAN NISHIMURA CO.,LTD. However, this digital PD meter has disadvantages that measuring mistakes or a measuring error tend to occur because the digital PD meter is pressed against a face of a subject to conduct measurement.
PD meters of product numbers NO.456 and NO.457 are also available from SAN NISHIMURA CO.,LTD. However, the PD meter of this type also has disadvantages that the PD meter does not solve the disadvantages of the digital PD meter and the measurement result of the PD meter tends to be deteriorated by convergence.