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The Visual Environment: Measurement and Design
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
The near point of vision is the closest distance at which an object can be brought into sharp focus. A 16-year-old can focus on an object less than 10 cm in front of the eye. However, the lens loses elasticity with age and, in practice, this results in a reduction in refractive power. By the age of 60 years, the near point may have receded to 100 cm. This is why older people often need reading glasses or, for example, have to hold the paper at arms length, when reading a newspaper. By the age of about 50 years, the lens has only about 2 D of accommodation left. After this, it can be regarded as completely non-accommodating—a condition known as presbyopia. The result of presbyopia is that the eye becomes focused at a fixed distance, which varies between different people depending on the characteristics and condition of their eyes. Frequently, the fixed viewing distance in the presbyopic eye is intermediate between the previous near and far points and the person has to wear bifocal lenses; the upper part is set for distant vision and the lower part for near vision (mainly for reading). Bifocal or trifocal lenses can restore a kind of stepwise accommodation to the presbyopic eye. In practice, if workplaces are adequately lit, the depth of field of the eye is increased and the net effect is to lower the requirements for accommodation. This explains why good lighting is important in all facilities used by older people. A more detailed discussion of accommodation may be found in Miller (1990).
C
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, general, optics] Adaptive optics instrument in the human eye that can be adjusted for focal length by contraction and relaxation of the muscle in the eye attached to the lens. When the muscles are relaxed the lens is most rounded with the image of the “near point” focused on the retina at approximately 24 mm from the lens. On contraction the lens flattens out, increasing the focal length, as defined by the lens equation, to the point of focusing “infinity” on the retina. The near point is at approximately 25 cm distance from the eye for the average adult, whereas children have a shorter near point (seeaccommodation) (see Figure C.88).
Perspectives on Designing Human Interfaces for Automated Systems
Published in Richard L. Shell, Ernest L. Hall, Handbook of Industrial Automation, 2000
Anil Mital, Arunkumar Pennathur
Visual displays: factors affecting design. Accommodation refers to the ability of the lens in the eye to focus the light rays on the retina. The distance (of the target object from the eye) at which the image of the object becomes blurred, and the eye is not able to focus the image any further, is called the near point. There is also a far point (infinity, in normal vision) beyond which the eye cannot clearly focus. Focal distances are measured in diopters. One diopter is 1/(distance of the target in meters). Inadequate accommodation capacity of the eyes result either in nearsightedness (the far point is too close) or in farsightedness (the near point is too close). Literature recommends an average focusing distance of 800 mm at the resting position of the eye (also known as the resting accommodation) [72]. Due to changes in the iris (which controls the shape of the lens), aging results in substantial receding of the near point, the far point remaining unchanged or becoming shorter. Figure 9 shows how the mean near point recedes with age. It is recommended that the designer use this information when designing visual displays.
Human Factors/Ergonomics (HFE) Evaluation in the Virtual Reality Environment: A Systematic Review
Published in International Journal of Human–Computer Interaction, 2023
Some studies suggested that VR causes visual fatigue and that changes in oculomotor parameters, such as negative relative accommodation, accommodative accuracy, and monocular and binocular accommodative facilities, are significantly different from those observed in reality (Alhassan et al., 2021; Munsamy et al., 2020). Some studies compared eye fatigue between a two-dimensional (2D) display and VR (Souchet, Philippe, et al., 2022). The aftereffects of VR showed changes in accommodation but no concomitant changes in vergence, which is probably due to the uncoupling of accommodation and vergence in VR (Szpak et al., 2019). However, some studies found no differences in visual fatigue between VR and the natural environment (Hirota et al., 2019). Turnbull and Phillips (2017) found no evidence that the optical arrangement VR harms the binocular status of the eyes in the short term. According to Yoon et al. (2020), there were no changes in refraction or accommodative factors after using VR. However, there was a significant increase in near point of accommodation (NPA), near point of convergence (NPC), and subjective symptom scores after dipping. In the study of VR, in which young adults wore a headset, no evidence was found that the optical arrangement of VR had a negative effect on the binocular status of the eyes in the short term (Turnbull & Phillips, 2017).
Premixed Flame Propagation of Methane/Carbon Monoxide/Air in a Closed Tube with an Obstacle
Published in Combustion Science and Technology, 2021
Zhijin Yu, Shuangshuang Chen, Yu Gu, Hu Wen, Ruikang Li, Shixing Fan
Figure 3 shows the pressure evolution of 9.5 vol.% CH4 explosions in a tube with or without an obstacle. From the results of 1st and 2nd pressure sensors, the pressure commenced to rise after ignition and a substantial influence of obstacle on the pressure increment and decrement process can be observed. The explosion pressure was weakened when the flame propagated to the obstacle, and it resulted in a decrease in the pressure increasing process and formed a pressure peak in the pressure curves. Then, when the flame propagated through the obstacle, the explosion pressure rises again and reaches the maximum. After the pressure-reflected wave passed through the obstacle, the pressure rises and a lower peak appeared. Due to heat loss, the explosion pressure decreases gradually. Meanwhile, because of affecting by an obstacle, the pressure wave oscillated in the tube and formed a regular fluctuation. This phenomenon is similar to the correlative previous study (Luo et al. 2020; Wan et al. 2018; Xiao et al. 2014). In addition, the obstacle curtailed the rate of pressure rise of the pressure wave at the far point from the obstacle, causing a weak peak in the pressure rise phase, whereas increased the rate of pressure rise of the pressure reflected wave at the near point of the obstacle, resulting in another weak peak in the pressure attenuation process.
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
In contrast, visual fatigue, which is the most common symptom experienced by computer users (Nakazawa et al. 2002; Blehm et al. 2005), has not been adequately studied with VR-HMDs. Normal binocular vision comprises vergence and accommodation systems that act simultaneously (Fincham and Walton 1957). Previous studies have demonstrated that visual fatigue is more likely to be induced by viewing three-dimensional (3D) images than by two-dimensional (2D) images (Hoffman et al. 2008; Shibata et al. 2011; Jeng et al. 2014) and have suggested that visual fatigue can result from binocular stress caused by vergence-accommodation conflict (Charles 1930; Kim, Kane, and Banks 2014; Kanda et al. 2012). Thus, previous studies investigated methods to objectively evaluate visual fatigue using vergence and accommodation parameters such as fusional vergence range, near point of convergence and high-frequency component in microfluctuations of accommodation (Berens, Hardy Le, and Pierce 1926; Rosenfield 2011; Sedaghat and Abrishami 2014; Kajita et al. 2001). However, there have been problems with reproducibility for both vergence (Berens, Hardy Le, and Pierce 1926; Rosenfield 2011; Sedaghat and Abrishami 2014) and accommodation (Maeda et al. 2011; Jeng et al. 2014).