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Paraxial Rays and Lenses
Published in Ajawad I. Haija, M. Z. Numan, W. Larry Freeman, Concise Optics, 2018
Ajawad I. Haija, M. Z. Numan, W. Larry Freeman
The power P of a thin lens placed in air is directly related to its focal length through the following definition: P=1/f, which, as suggested by Equation 3.4, for a thin lens of an index of refraction n1 placed in a medium of an index of refraction n2, becomes P=n2−n1n11R1−1R2. For any thin lens, the sign of the power P follows the sign of its focal length f. Thus for a positive lens, P is positive, and for a negative lens, P is negative. For a focal length in meters, the units of P are in m−1. In optics, this unit is called the diopter, symbolized by D.
Optical Components
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
The inverse of focal length measured in meters gives the power of the lens in diopters. Therefore the power P of a thin lens is P=1f=(n−1)(1R1−1R2)
D
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[general, optics] The power of a lens, captured as the reciprocal value of the focal length. Due to its definitions, the lens power in diopters is additive. For vision correction, a far-sighted person needs to gain close distance vision by means of a lens system with a positive value, whereas near-sightedness can be corrected by a negative diopter lens. A positive diopter lens is a magnifier, whereas a negative diopter will result in a virtual image.
Visual fatigue induced by watching virtual reality device and the effect of anisometropia
Published in Ergonomics, 2021
Sang Hyeok Lee, Martha Kim, Hyosun Kim, Choul Yong Park
The participants visited a total of three times after passing the screening test. Each visit was separated at least 1 week. In the first visit, the refractive errors of both eyes were fully corrected using the trial lens and frame, and the participants were instructed to watch a VR video. In the second visit, a spherical lens of +1 dioptre was intentionally added to the refractive correction of the dominant eye, inducing an anisometropia, and the participants were instructed to watch a VR video. In the third visit, the same amount of anisometropia was induced in the non-dominant eye. In general, an anisometropia of 1.5 dioptres or more can cause aniseikonia, which can also increase eye fatigue. Therefore, we induced an anisometropia of 1 dioptre to avoid the inadvertent effect of aniseikonia in this study. Manifest refraction of the participants was measured both before and after watching VR on every visit. Manifest refraction is the traditional way to determine the refractive error of the patient without cycloplegic eyedrops. The average of three independent measurements was used for the analysis.
News and Product Update
Published in Journal of Medical Engineering & Technology, 2023
The e-scope® pocket otoscope is a lightweight, economical otoscope from Rudolf Riester GmbH that is ideally weighted and sized to be carried in a pocket all day. The otoscope uses AA alkaline batteries (sold separately), employs a pen clip to easily keep it in place, and comes with varied illumination. e-scope® otoscopes are available with halogen or vacuum direct illumination, fibre optic xenon (3200K) or fibre optic 3.7 V LED (5500K). With respect to the latter, a tiny IPC inside the e-scope® always converts the voltage of conventional AA-size batteries into the optimum voltage supply for LEDs, enabling efficient operation of LED illumination with alkaline batteries. As a result, the IPC not only ensures optimum light quality, but also provides economic and ecological benefits. With this innovation, the service life of a light-emitting diode is up to 1,000 times longer than that of xenon illumination and the batteries used in the e-scope® are discharged considerably more thoroughly thanks to the IPC; consequently, they do not need to be disposed of and replaced as often. The LED burns for at least 20,000 h, i.e. over 2 years at a go with e-scope®, even with two conventional AA batteries. Other features include a Dioptre disc with 18 corrective lenses (± 1, 2, 3, 4, 6, 8, 10, 15, 20 dioptres), an easy-to-use aperture wheel with six different apertures (fixation star, large circle, small circle, red free filter, blue filter, semi-circle) and high-performance optics with an aspherical condenser lens. The otoscope has sealing precision optics pivotable to both sides with 3x magnification for optimum view, replete with a sturdy ear specula receptacle in hardwearing hygienic metal.
Comparison of visual fatigue caused by head-mounted display for virtual reality and two-dimensional display using objective and subjective evaluation
Published in Ergonomics, 2019
Masakazu Hirota, Hiroyuki Kanda, Takao Endo, Tomomitsu Miyoshi, Suguru Miyagawa, Yoko Hirohara, Tatsuo Yamaguchi, Makoto Saika, Takeshi Morimoto, Takashi Fujikado
Twelve subjects aged 26.7 ± 4.1 years [mean ± standard deviation; range, 22–36 years] were enrolled in this study (Table 1). The mean refractive errors (spherical equivalent, SE) of the subjects’ right and left eyes were −1.90 ± 1.53 D (dioptre) and −1.81 ± 1.67 D, respectively. The best-corrected visual acuity at distant for all subjects was equal to or better than 0.0 logMAR (minimum angle of resolution). The mean near point of convergence was 2.16 ± 1.95 cm. The mean fusional vergence range was 29.0 ± 10.5 prism dioptre (PD), and all subjects had a stereoacuity of 1.60 log arcsec. The mean angles of deviation at near and distance were 8.1 ± 9.1 and 1.6 ± 3.6 PD, respectively.